Annual report

The
International
Rice Research
Institute
Annual Report

for 1973

The International Rice Research Institute
Annual Report for 1973

Correct citation: International Rice Research
Institute. 1974. Annual Report for 1973. Los
Bahos, Philippines.

The International Rice Research Institute
Annual Report for 1973

The International Rice Research Institute, Los Bahos, Laguna, Philippines, 1974

Contents

vi BOARD OF TRUSTEES
vii PERSONNEL
ix ABOUT THIS REPORT
xi RESEARCH HIGHLIGHTS
xi Prelude
xiii Rice-food of the low-income masses
xvi Genetic Evaluation and Utilization (GEU)
xxxvi Finances
xxxvii Staff changes
xxxviii Trustees
xxxix CROP WEATHER
1 CHEMISTRY
2 Grain protein
3 Grain quality
9 Seed and plant metabolism
15 MULTIPLE CROPPING
16 Cropping systems program
16 Lessons from traditional technology
25 Varietal testing of component crops
26 Crop management techniques
28 Agronomic and economic factors
35 STATISTICS
36 Factors limiting farmers' yields
39 Variability in protein content
42 Yield response to nitrogen
44 Soil heterogeneity
45 Designs for multiple cropping trials
47 PLANT PHYSIOLOGY
48 Climatic influence on yield
50 Physiology of drought resistance
53 Screening for drought resistance
55 Photosynthesis
56 Nitrogen sources and nutritional disorders
57 Upland rice
59 Volunteer rice
61 Survival of submerged seedlings
61 Photoperiod
61 Autecology of Scirpus maritimus L.
65 AGRONOMY
66 Nitrogen response in irrigated rice
68 Practices for irrigated rice
72 Rainfed paddy culture
74 Upland rice
83 Drought tolerance
89 Varietal adaptation to water conditions
90 High protein rices
93 SOIL CHEMISTRY
94 Chemical kinetics of submerged soils
96 Fertilizer-saving cultural practices
100 Varietal resistance to soil problems
104 Rainfed rice

107 SOIL MICROBIOLOGY
108 Atmospheric nitrogen fixation
111 Transformation of nitrogen
113 Mineral transformation
114 Organic matter transformation
115 Pesticide residues
117 PLANT PATHOLOGY
118 Blast
118 Sheath blight
120 Improving sources of resistance to diseases
121 Bacterial blight
127 Epidemiology of tungro
135 Tungro vectors at the IRRI farm
136 Tungro in Luzon
139 Screening for tungro resistance
139 Grassy stunt
143 VARIETAL IMPROVEMENT
144 Breeding program
160 Rice germ plasm bank
161 Genetics and cytogenetics
167 AGRICULTURAL ENGINEERING
168 Machine design and testing
174 Economics of mechanization
181 AGRICULTURAL ECONOMICS
182 World production and demand for rice
183 Changes in rice farming in Asia
192 Barriers to higher yields and income
197 Water management
209 ENTOMOLOGY
210 Varietal resistance
213 Insecticides
223 Biological control of insects
225 Integrated control
232 Ecology of rice insects
235 RICE PRODUCTION TRAINING AND RESEARCH
235 Training programs
236 Applied research trials
237 Rainfed and upland rice project
247 TRAINING PROGRAMS
251 INTERNATIONAL ACTIVITIES
251 International testing
256 International conferences
257 INFORMATION RESOURCES AND EXPERIMENTAL FARM
257 Library and documentation center
257 Information services
257 Experimental farm
259 PUBLICATIONS AND SEMINARS
259 Publications
261 Seminars
263 INDEX

Board of trustees

DR. FORREST F. HILL, chairman
The Ford Foundation, U.S.A.

MR. M. D. BANDA
Ceylon

DR. VIRGILIO BARCO
Executive director, International Bank for Reconstruction and Development, U.S.A.

DR. NYLE C. BRADY
Director, The International Rice Research Institute

DR. CLARENCE C. GRAY, III
Deputy director for agricultural sciences, The Rockefeller Foundation, U.S.A.

DR. TOJIB HADIWIDJAJA
Minister of Agriculture, Indonesia

DR. TOSI TAKE IIDA
Director, Institute for Plant Virus Research, Japan

DR. SALVADOR P. LOPEZ
President, University of the Philippines

GEN. FLORENCIO MEDINA
Chairman, National Science and Development Board, Philippines

DR. S. V. S. SHASTRY
Project coordinator, All-India Coordinated Rice Improvement Project

MR. C. SUBRAMANIAM
Minister of Industrial Development and Science and Technology, India

MR. ARTURO R. TANCO, JR.
Secretary of Agriculture and Natural Resources, Philippines

Personnel
ADMINISTRATION
Nyle C. Brady, Ph.D.. director
Dilbagh S. Athwal, Ph.D., associate director
Marcos R. Vega, Ph.D. assistant director
Faustino M. Salacup, B.S., C.P.A., executive officer and
treasurer
Zosimo Q. Pizarro, LL.B. associate executive officer
Pedro G. Banzon, LL.B., administrative associate
Ifor B. Solidum, LL.B., administrative associate*
Purita M. Legaspi, B.B.A., C.P.A., assistant treasurer
Hermenegildo G. Navarro, B.S., property superintendent
Rebecca C. Pascual, M.S., manager, food and dormitory
services
AGRICULTURAL ECONOMICS
Randolph Barker, Ph.D.. agricultural economist
Thomas H. Wickham, Ph.D., associate economist
Robert W. Herdt, Ph.D., visiting agricultural economist
Rodolfo D. Reyes, M.S., senior research assistant
Teresa L. Anden, A.B., research assistant
Violeta G. Cordova, B.S., research assistant
Ricardo A. Guino, B.S., research assistant
Abraham M. Mandac, B.S., research assistant
Fe A. Bautista, B.S., research aide
Geronimo E. Dozina, Jr., B.S., research aide
Oscar B. Giron, B.S. research aide
Eloisa M. Labadan, B.S., research aide
Adelita C. Palacpac, B.S., research aide
Alfredo B. Valera, B.S., research aide
AGRICULTURAL ENGINEERING
Amir U. Khan, Ph.D., agricultural engineer
Bart Duff, M.S., associate agricultural economist
Fred E. Nichols, B.S., associate evaluation engineer
Joseph K. Campbell, M.S., visiting associate agricultural
engineer
Jose S. Policarpio, B.S., assistant design engineer*
Antero S. Manalo, M.S., assistant agricultural engineer
Jose R. Arboleda, M.S., senior research assistant
Nestor C. Navasero, B.S., senior research assistant
Norberto L. Orcino, B.S., senior research assistant
Consorcio L. Padolina, M.S., senior research assistant
Edgardo G. del Rosario, B.S., research assistant*
Guillermo J. Espiritu, B.S., research assistant
Simeon A. Gutierrez, B.S., research assistant
Zenaida F. Toquero, M.S., research assistant
Ida E. Estioko, B.S., research aide*
Bibiano M. Ramos, B.S., research aide
Benigno T. Samson, B.S., research aide
Luzviminda F. Lumang, research aide
Benjamin D. Buan, B.S., draftsman
Fernando S. Cabrales, B.S., draftsman
Feliciano C. Jalotjot, draftsman
AGRONOMY
Surajit K. De Datta, Ph.D., agronomist
Jose A. Malabuyoc, M.S., assistant agronomist
Jesus T. Magbanua, B.S., senior research assistant*
Pablo M. Zarate, B.S., research assistant
Paul C. Bernasor, B.S., research assistant
Rene Q. Lacsina, B.S., research assistant
Wenceslao P. Abilay, B.S., research assistant
Ernesto I. Alvarez, B.S., research assistant
Wilma N. Obcemea, B.S., research aide
Clarissa G. Custodio, B.S., research aide*
Mae T. Villa, B.S., research aide

CHEMISTRY
Bienvenido O. Juliano, Ph.D., chemist
Gloria B. Cagampang, M.S., assistant chemist
Consuelo M. Perez, M.S., senior research assistant
Bernardita V Esmama, B.S., research assistant
Ruth U. Monserrate, B.S., research assistant
Evelyn P. Navasero, M.S., research assistant
Adoracion P. Resurreccion, M.S., research assistant
Lyda B. Suzuki, M.S. research assistant*
Alicia A. Perdon, B.S., research aide

ENTOMOLOGY
Mano D. Pathak, Ph.D., entomologist
V. Arnold Dyck, Ph.D., associate entomologist
Fausto L. Andres, B.S., senior research assistant
Gerardo B. Aquino, B.S., research assistant
Carlos R. Vega, B.S., research assistant
Denis T. Encarnacion, B.S., research assistant
Tomas D. Cadatal, M.S., research assistant
Caesar D. Pura, M.S., research assistant*
Arlando S. Varca, B.S., research assistant
Henry C. Dupo, B.S., research assistant
Gloria C. Orlido, B.S., research assistant
Conrado R. Nora, B.S., research assistant
Lourdes A. Malabuyoc, B.S., research aide
EXPERIMENTAL FARM
Federico V. Ramos, M.S., associate agronomist and farm
superintendent
Orlando G. Santos, B.S., associate farm superintendent
Juan M. Lapis, B.S., senior farm supervisor
Eladio M. Baradas, B.S.,farm supervisor
Filomeno O. Lanting, B.S.,farm supervisor

INFORMATION SERVICES
Steven A. Breth, M.A., editor
Thomas R. Hargrove, M.S., associate editor
Coraz6n V. Mendoza, M.S., assistant editor
Ramiro C. Cabrera, B.F.A., graphic designer
Arnulfo C. del Rosario, B.S., artist-illustrator
Federico M. Gatmaitan, Jr., artist-illustrator
Urbito T. Ongleo, B.S., photographer
Feliciano J. Toyhacao, assistant photographer
Simeon N. Lapiz, assistant photographer
Sesinando M. Masajo, B.S., rice information assistant

LIBRARY AND DOCUMENTATION CENTER
Lina Manalo-Vergara, M.S., chief librarian
Milagros C. Zamora, M.S., assistant librarian
Mila M. Ramos, B.L.S., catalog librarian
Carmelita S. Austria, B.L.S., order librarian
Fe C. Malagayo, B.L.S., circulation librarian
Rosalinda M. Temprosa, B.S.E., indexer
Jukyu Cho., translator (in Japan)*
Masatada Oyama, D.Agr., translator (in Japan)*
Mieko Honda, B.A., indexer (in Japan)
Kazuko Morooka, indexer (in Japan)

MULTIPLE CROPPING
Richard R. Harwood, Ph.D., agronomist
Gordon R. Banta, M.S., visiting associate agricultural
economist
Wilhelmino A.T. Herrera, B.S., senior research assistant
Avelito M. Nadal, B.S., research assistant*
Roberto T. Bantilan, B.S., research assistant
Maximo B. Obusan, B.S., research assistant

Samuel P. Liboon, B.S., research assistant
Manuel C. Palada, M.S., research assistant
PLANT PATHOLOGY
Shu-Huang Ou, Ph.D., plant pathologist
Keh-Chi Ling, Ph.D., plant pathologist
Harold E. Kauffman, Ph.D., plant pathologist
Fausto L. Nuque, M.S., assistant plant pathologist
Celestino T. Rivera, M.S., assistant virologist
Jose M. Bandong, M.S., senior research assistant
Vladimarte M. Aguiero, B.S., research assistant
Toribio T. Ebron, B.S., research assistant
Silvino D. Merca, B.S., research assistant
Marina P. Natural, B.S., research assistant*
Manolito P. Carbonell, B.S., research assistant
Alberto G. de la Rosa, B.S., research assistant
Sonia P. Ebron, B.S., research aide
PLANT PHYSIOLOGY
Shouichi Yoshida, D.Agr., plant physiologist
Benito S. Vergara, Ph.D., plant physiologist
Masaki Hara, Ph.D., visiting scientist
Francisco T. Parao, M.S., assistant plant physiologist
Victoria P. Coronel, B.S., research assistant
Evangelina de los Reyes, B.S., research assistant
Aurora M. Mazaredo, B.S., research assistant
Romeo M. Visperas, B.S., research assistant
RICE PRODUCTION TRAINING AND RESEARCH
Vernon E. Ross, M.S., rice production specialist
Inocencio C. Bolo, B.S., assistant rice production specialist
Eduardo R. Perdon, B.S., assistant rice production specialist
Eustacio U. Ramirez, B.S., rice production technician
Leopoldo M. Villegas, M.S., rice production technician
Jose I. Calderon, B.S., rice production technician
Rizalino T. Dilag, Jr., B.S., rice production technician
Leonardo T. Almasan, research aide
SOIL CHEMISTRY
F. N. Ponnamperuma, Ph.D., soil chemist
Ruby U. Castro, M.S., assistant chemist
Rhoda S. Lantin, M.S., senior research assistant
Myrna R. Orticio, B.S., research assistant
Oscar C. Reyes, B.S., research assistant*
Nicolas M. Chavez, B.S., research assistant
Socorro S. Raval, B.S., research assistant
SOIL MICROBIOLOGY
Tomio Yoshida, Ph.D., soil microbiologist
Hitoichi Shiga, D.Agr., visiting scientist
Teresita F. Castro, B.S., senior research assistant
Diana C. del Rosario, B.S., research assistant
Wilbur B. Ventura, M.S.. research assistant
Benjamin C. Padre., Jr., research assistant
STATISTICS
Kwanchai A. Gomez, Ph.D., statistician
Emerito V. Tipa, B.S., research assistant*
Emeterio Solivas, B.S., research aide*
Leticia Postrado, B.S., research aide*
Teodora Oliveros, B.S., research aide*
Dominador Torres, B.S., research aide
Erlinda Go, B.S., research aide
Sally Gesmundo, B.S., research aide

PLANT BREEDING
Gurdev S. Khush, Ph.D., plant breeder
Te-Tzu Chang, Ph.D., geneticist
W. Ronnie Coffman, Ph.D., associate plant breeder
Antonio T. Perez, Ph.D., assistant visiting scientist
Rodolfo C. Aquino, M.S., assistant plant breeder
Rizal M. Herrera, B.S., senior research assistant
Jose C. de Jesus, Jr., B.S., senior research assistant
Esperanza H. Bacalangco, B.S., research assistant
Normita M. de la Cruz, B.S., research assistant
Agapito M. Gonzalvo, Jr., B.S., research assistant
Vicente T. Librojo, Jr., B.S., research assistant
Genoveva C. Loresto, M.S., research assistant
Carmen M. Paule, B.S., research assistant
Eugenio S. Sarreal, B.S., research assistant
Oscar 0. Tagumpay, B.S., research assistant
Espiridion T. Torres, B.S., research assistant
Reynaldo L. Villareal, B.S., research assistant
Alicia A. Capiral, B.S., research aide
Angelita P. Marciano, B.S., research aide

STAFF IN INTERNATIONAL PROGRAMS
BANGLADESH
Rufus K. Walker, M.S., rice adviser*
EGYPT
Kunio Toriyama, D.Agr.Sc., project specialist
INDONESIA
Emiterio V. Aggasid, B.S., experiment station development
engineer
Henry M. Beachell, M.S., plant breeder
Jerry B. Fitts, Ph.D., agronomist
Russell D. Freed, Ph.D., plant breeder
John M. Green, Ph.D., corn breeder and seed certification
specialist
Robert I. Jackson, Ph.D., joint coordinator, National Rice
Research Program
Cezar P. Mamaril, Ph.D., research administration specialist
Jerry L. McIntosh, Ph.D., agronomist
Richard A. Morris, Ph.D., statistician
INDIA
Reed C. Bunker, Ph.D., entomologist*
Wayne H. Freeman, Ph.D., joint coordinator, All-India
Coordinated Rice Improvement Project
Ernest W. Nunn, B.S., agricultural engineer*
Hiroshi Sakai, Ph.D., plant physiologist*
PHILIPPINES
Reeshon Feuer, Ph.D., crop production specialist
SRI LANKA
William G. Golden, Jr., M.S., rice specialist
James E. Wimberly, M.S., rice processing adviser
VIETNAM
Robert P. Bosshart, Ph.D., agronomist
Dwight G. Kanter, Ph.D., rice breeder

*Left during year

About this report

This is the 12th annual report of the International Rice Research Institute since
it was founded in 1960. The major financial supporters of IRRI are the Ford
Foundation, The Rockefeller Foundation, U.S. Agency for International
Development, The Overseas Development Administration (U.K.), the Inter-
national Development Research Centre (Canada), and the Japanese govern-
ment. This report covers work done during the 1973 calendar year.
Data in the report are given in metric units, e.g. "t/ha" means metric tons per
hectare. Unless otherwise stated, "control" means untreated control, grain
yield is calculated as rough rice at 14 percent moisture, and protein content is
calculated as a percentage of brown rice at 14 percent moisture. A single
asterisk (*) means significant at the 5-percent level, a double asterisk (**) means
significant at the 1 % level, but if value for a control is given, a single asterisk
means significantly different from the control at the 5 % level and a double
asterisk means significantly different from the control at the 1 % level.
Because of the increasing complexity of the breeding program, the system for
indicating pedigrees has been changed. Instead of the multiplication sign ( x) a
slant bar (/) is used. For example IR22 x IR24 is now written IR22/IR24. The
sequence of crosses is indicated by the number of slant bars: (IR22 x IR24) x
CR94-13 is now written IR22/IR24//CR94-13. The fourth and further crosses
are designated /4/, /5/, and so on. Backcrosses are indicated by a superscript
numeral.
The report frequently mentions three fundamental types of rice culture.
Upland culture means rice grown without irrigation in fields without bunds.
Rainfed paddy culture means rice grown without irrigation but in fields that are
bunded to impound rainfall. Irrigated or flooded culture means rice grown with
irrigation in bunded fields.
The thumb index on the back cover provides quick access to any research
section. To use it, bend the book in half and follow the margin index to the page
with the black edge marker.

Research highlights

The world food situation remains serious. Bad weather cut rice and wheat production
by 10 percent in some countries in 1972. Most of the poor and over-populated
countries, where two-thirds of mankind lives, were already importing food. A world-
wide food shortage prompted spiralling prices; the poorest of the poor suffered the
most.
The weather was generally favorable and the crops were good in 1973, relieving
somewhat the food crisis. Still, food prices remain high and some Asian cities have
been torn by food riots. Even more shocking, prolonged drought has scorched
the earth and brought famine to sub-Sahara Africa.
The 1973 energy shortage sharply reduced the supply of chemical inputs-the
fertilizers and pesticides that farmers need for high yields. Input costs are sharply
rising, particularly for vital nitrogen fertilizer. The hungry nations are being hit
hardest of all because they don't have the capital to compete with the more developed
nations for the limited chemical inputs.
Population pressures continue to mount in these poor nations. The earth's popula-
tion today is 3.8 billion, and is increasing at 2 percent per year. It will double by the
year 2000. In the poor nations, population is increasing at a rate of 2.5 percent per
year, and will double in about 25 years.
In the past, the developed nations had large buffer grain reserves to help feed the
growing numbers in the less fortunate countries if crops failed. No such grain reserves
exist today.
Some think that the grave predictions of 18th century economist Thomas Malthus
are inevitable-that man's numbers will outdistance his capacity to produce food, and
the world will slide into a nightmare of famine, pestilence, social decay, and wars for
limited land.
We at the International Rice Research Institute are more optimistic. We are
applying science to agriculture, to help raise food production in the hungry nations
enough to avert famine and even to curtail widespread hunger until man learns to
control his numbers. The low-income farmer who lacks the skills and resources to use
modern chemical inputs will be helped by IRRI's new rices which are resistant to
major insects and diseases. Fertilizer practices and pest control methods have been
specially tailored for the small farmer. Techniques of packaging practices for country-
wide rice production programs have been tested. Innovative multiple cropping
systems to induce more food production from the limited land are being evaluated and
improved. The potential for increasing production has never been greater.
If resources are available to capitalize on past successes, IRRI scientists can
continue to chart the way to higher yields and more dependable food production.
These achievements are essential if man is to feed himself while the earth's population
growth is being brought under control.

PRELUDE

RESEARCH HIGHLIGHTS xi

1. Rice is the primary or secondary staple food of nine-tenths of the low-income people in the most
densely populated regions of the world. (a) Population density and low-income areas. (b) Rice production
and low-income areas.

xii IRRI ANNUAL REPORT FOR 1973

Rice truly means life itself to the world's poorest and most densely populated regions.
A third of mankind-1.3 billion people-depends on rice for more than half of its
food. For another 400 million people, rice is a major secondary staple, providing from
25 to 50 percent of their total food. In some countries, rice supplies more than half of
the total protein consumed.
Rice is the primary or secondary staple food of nine-tenths of the low-income people
of the most densely populated regions of the world (fig. 1). The average annual income
of those who depend primarily on rice is only $80.
Population increases in most rice-consuming countries are among the highest in the
world. Consequently, demands for rice are expected to increase by 30 percent in the
next 10 years. Some countries which have traditionally exported rice are now having
difficulty producing food for their own populations.
The precarious balance between supply and demand for rice is illustrated by the
effect of adverse weather conditions in 1972 on the adequacy of the supply of rice and,
especially, on its price (fig. 2). When rice became limited, prices doubled and even
tripled within a few months in some countries. Such instability most severely affected
those least able to pay the soaring prices. For example, in the Philippines, the poorest
people, who were already spending 37 percent of their meager incomes on rice before
the price increase, would have to spend 74 percent after the price increase if they
continued to purchase the same amount of rice. Thus, abundant rice production is
critical not only to the hundreds of millions of rice farmers struggling to make a living
on their 1- to 2-hectare farms, but also to the landless laborers and to the low-income
workers in villages and cities. Anyone seriously concerned with the welfare of the poor
and the hungry must be concerned with rice.
Improved weather conditions have brought relief to rice farmers and consumers
alike. Abundant yields in 1973 appear to have averted widespread hunger. But the
demand for rice is still high; so is its price. National storage stocks have not been built
up to the 1971 levels.
The scarcity and high price of fertilizers and other agricultural chemicals add to the
mounting problems of all farmers, particularly those with low incomes. With credit
uncertain and costly, the small farmer can not compete for the scarce supplies of
chemicals and other inputs needed to capitalize on the productive potential of new
rice varieties.
In spite of the impressive technological advances of the past decade, national
production figures show increases barely high enough to meet population growth. The
experiences of the past few years remind us that the production revolution needed to
feed rice consumers has only begun. Accomplishments such as those summarized in
this report give us a glimpse of what science can do to help accelerate this revolution.
They also show how IRRI's research and training programs are already helping many
low-income farmers and their city or village counterparts, and how expansion of these
programs can be relied on to reach many more.
Progress has been made. The problems of the small rice farmer continue to receive
primary attention of IRRI scientists. Following up on the successes of IR8, IR5, IR20,
and other high-tillering, fertilizer-responsive, semidwarf varieties, we have broadened
our focus in recent years to include other improvements of the rice plant. These
improvements will help farmers control disease and insect pests, obtain reasonable
yields in spite of droughts or floods, and grow rice on poor soils.
IRRI's first rice variety, IR8, demonstrated that the productive potential of rice
can be substantially raised by selective breeding. Scientists screened, crossed, and

RICE-
FOOD OF
THE LOW-
INCOME
MASSES

RESEARCH HIGHLIGHTS xiii

Price ($/t)
125
UREA
100-

75 -

50 I i I
55 57 59 61 63 65 67 69 71 73
Yeor

2. World demand, production, and lagged price of rice (upper), and
price of urea (lower), 1953-73.

selected until they developed a rice which had the characteristics they sought: a
semidwarf plant type with a stiff straw. When fertilized, the strong stem holds the
plant upright, not allowing it to topple. Extra plant nutrients, added as fertilizer, are
converted to more grain.
Most modern rices which followed IR8 were of the semidwarf plant type. By 1972,
semidwarf rices were grown on 16 million hectares in South and Southeast Asia,
about 20 percent of the area's rice land. Of Latin America's 62 million hectares of rice
land, about 0.6 million are now planted to stiff-strawed varieties developed to a
considerable extent from IRRI genetic material. About 90 percent of the irrigated
rice areas in some Latin American countries are planted to these high-yielding
varieties.
Average farm yields are steadily increasing in nations where the new rices have been
adopted. Still, actual rice production in the poor nations is far less than potential
production. We are now identifying the major constraints to higher rice yields, and
are organizing to systematically develop improved varieties and technologies that will
overcome these production constraints.
IR26 and tomorrow's companions. Great strides were made during 1973 in IRRI's
genetic improvement program. A new variety, IR26, was released. It has good grain

xiv IRRI ANNUAL REPORT FOR 1973

Variety Lodging

IR8 R

IR5 MR

IR20 MR

IR22 R

IR24 R

IR26 MR

Diseases
Bacterial Bacteria Grassy
Blast blight sek stunt Tungro
blight streak stunt

MR S S S S

S S MS S S

MR MR S =R

S 4 MS S S

S S MR S MR

MR W. MR MR _.
. __ __ *

Insects Soil problems
Green Brown Stem Alkali Salt Iron Reduc-
e r hlont- borer injury injury toxicity ; cts
hopper hopper
R S MS S MR S MR

R S S S MR S MS

R S MR S MR P MR

S S S S S MR MR

, R S S MR MR MR MS

;-' 'r. MR MR MR R MR
: .::- ... ., .

3. Resistance ratings of IRRI varieties. R = resistant; MR = moderately resistant; MS = moderately
susceptible; S = susceptible.

quality and yielding ability. But more important, it has moderate to high levels of
resistance to seven major insect pests and diseases (fig. 3), including the brown plant-
hopper which has become a major threat in the Philippines, South Vietnam, Sri Lanka,
and parts of India. This variety is expected to spread rapidly into these hopper-infested
areas as well as into regions where tungro virus, green leafhoppers, and blast have been
problems in the past.
The development of IR26 continues the trend set by IR20, emphasizing insect and
disease resistance. In IRRI's breeding pipeline are other potential varieties with
welcome resistance to major insects and diseases. Two more breeding lines in advanced
testing have resistance or moderate resistance to seven of the most serious disease and
insect pests; six other lines have the same degree of resistance to six such pests; and
four more lines have resistance to five.
Remarkable progress is being made in introducing resistance to insects and
diseases. In 1973, 70 percent of the 185 entries in the annual replicated yield trials at
IRRI had multiple resistance to at least five important disease and insect pests. The
comparable figure in 1972 was only 5 percent. IRRI's scientists are making headway
in blending insect and disease resistance into lines already known to have good grain
quality and yielding ability.
Another measure of the progress at IRRI in the genetic improvement of the rice
plant is the number of crosses being made. More than 2,000 such crosses were made in
1973, double that accomplished in 1972 and five times the number crossed in 1971.
We consider such high-volume crossing essential because desirable genetic characters
are often associated with bad ones. We must make a large number of crosses to
incorporate combinations of favorable plant characters into high-yielding lines.
We expedited our hybridization (crossing) effort by constructing a simple "vacuum
emasculator" to speed up the removal of unwanted anthers from the florets. This
replaces the time-consuming conventional method of using forceps to manually
remove the anthers. By the new suction technique, an operator can emasculate 425
florets per hour, compared with 250 using the conventional method. We are releasing
the design of this inexpensive machine on request to other plant breeding teams.
Adaptation of varieties. Modern varieties developed by IRRI scientists and their
cooperators are being widely grown by farmers in rainfed areas as well as those in

RESEARCH HIGHLIGHTS xv

irrigated regions. The characteristics of the new stiff-strawed semidwarfs appear to
make them as adaptable to rainfed as to irrigated conditions. This illustrates the wide
adaptability of our breeding materials.
Cooperation with national programs. We continued our efforts to help cooperating
country programs develop and improve rice varieties suitable for their local condi-
tions. In 1973, we sent 7,618 seed packages of breeding lines to research workers in 45
countries. Some of these lines are being used as parents in the national breeding
programs. Others are being tested directly for their adaptability to local conditions.
A total of 25 IRRI breeding lines so tested have been released as commercial varieties
by other countries, six of them this year.
Examples of the adaptability of these lines are: "Parwanipur 1" (IR400-29-9)-an
early maturing line adapted to the foothills of the Terai region in Nepal; varieties "R"
(IR1052) and "S" (IR1055)-two long-grained selections, named in Guyana, with
quality characteristics especially suited to that area of the world; "Thon Nong 73-1"
(IR1529-680-3)-a high-yielding selection named in Vietnam with sturdy stems and
excellent grain quality, and resistant to blast, bacterial blight, and green leafhoppers.

GENETIC We further systematized IRRI's coordinated rice improvement program in 1973 by
EVALUATION formalizing an institute-wide Genetic Evaluation and Utilization (GEU) program.
AND Interdisciplinary and problem-oriented rice breeding is the backbone of GEU. Plant
breeders are teamed up with "problem area" scientists, such as plant pathologists,
UTILIZATION entomologists, and cereal chemists. Each team member contributes his specialized
(GEU) knowledge to the joint effort to identify, screen, and cross diverse rices. By so doing,
the best characteristics can be incorporated into nutritious rice varieties which resist or
tolerate the environmental and pest enemies of the rice plant (fig. 4). Major GEU
problem areas include:
resistance to diseases
resistance to insects
high protein levels
tolerance to drought
tolerance to toxic soils
tolerance to deep water
tolerance to cold
Figure 5 shows the flow of rice germ plasm or genetic material through the GEU.
The 30,000-sample germ plasm bank is the primary source of genetic materials. From
this bank, promising varieties from all over the world are screened to determine which
have desired characteristics to use in crossing, or hybridization, programs.
Hybridization and screening of the progeny provide lines which can be tested at
IRRI and shared with cooperating country programs throughout the world. The
ultimate objective of GEU is to help these country programs develop and place in the
hands of farmers new varieties with characteristics suited to local conditions.
The nature of the GEU screening and field evaluation demands close interdisci-
plinary cooperation, which has always been a strong feature of IRRI's rice improve-
ment program. Such cooperation is responsible for the results described in the
following sections.
Germ plasm conservation. The hub of the GEU program is IRRI's growing germ
plasm bank, which now contains more than 30,000 of the world's estimated 100,000
varieties.

xvi IRRI ANNUAL REPORT FOR 1973

N

IL

CHARACTERS PB 7

89t

DISEASE AND
INSECT RESISTANT
VARIETIES
GENETICALLY
ADAPTED TO
ADVERSE FACTORS

i~i~I

I /8

4. Superior agronomic characteristics and disease and insect resistance will be incorporated into all new
rice varieties developed through the Genetic Evaluation and Utilization (GEU) program. Plant breeders
(PB) and problem area scientists (PA) will work together to incorporate the ability to withstand other
production constraints.

Many of these varieties yield poorly but have inherent genetic characteristics,
evolved or selected over centuries, that adapt them to specific environmental condi-
tions (such as rices that grow on toxic soils or rices that are tolerant to drought).
Many of these rices face the threat of extinction. Farmers often abandon their
traditional rices as they adopt high-yielding varieties. Encroaching urbanization and
resource exploitation wipe out wild and primitive species. When such rice strains
disappear, the invaluable genes which carry the desirable characters from one
generation to the next, also vanish.

I(PS)I COUNTRY
LLOGAMS

5. The flow of germ plasm through the GEU.

RESEARCH HIGHLIGHTS xvii

IRRI cooperates with rice specialists throughout the world to locate, collect, and
preserve as many rice strains as possible, including those of unknown potential, before
these strains disappear. During 1973, IRRI scientists helped in germ plasm collection
efforts in Bangladesh, Burma, East Malaysia, Indonesia, the Khmer Republic, the
Philippines, and South Vietnam. We collected many special types reported to be
resistant to salinity, tolerant to acid-sulfate soils, or resistant to drought.
Almost 4,000 new accessions were saved and added to the germ plasm bank during
1973. Scientists in 38 countries draw nearly 10,000 seed samples from the bank to use
in national breeding programs.
Agronomic characteristics. In some countries varieties with intermediate plant type,
represented by IR5 (120 cm high), are more popular for lowland rice production than
the shorter statured varieties, such as IR8 (100 cm high). Strains with intermediate
heights are also favored for upland conditions. Consequently, we are introducing
genes for intermediate stature into lines known to be resistant to the major insects and
diseases and to have high tillering capability, erect leaves, and sturdy stems.
In response to the growing demand for short-seasoned varieties, we have developed
lines which mature in about 105 days. For comparison, IR8 matures in 130 days. The
short-seasoned IR2061 selections are the most promising of these new lines. Their
grain qualities are good; their insect and disease resistance remarkable; and their
yields are among the highest of the early maturing selections.
We continued to improve grain quality to satisfy the tastes of rice consumers in
different parts of the world. We are blending the qualities of desired amylose content,
aroma, and stickiness into lines with high resistance to insects and diseases.
Disease resistance. Rice is often cultivated year-round in the hot, humid tropics.
These conditions encourage rapid buildups of pathogenic organisms. The breeding of
resistant varieties is the most practical way to control diseases. Continuing efforts are
being made to screen varieties and hybrid progenies for resistance to major diseases
and to study the behaviors of the different pathogens.
We have found that races of the variable blast fungus disease (Pyricularia oryzae)
constantly change in the field. For example, in an epidemic in the 1973 upland variety
trial, we found 11 races out of 46 isolates tested from the same field. Ten of the 11 races
are new to the Philippines. The 10 new races attacked CO25, which was resistant to most
races in previous tests, but they did not infect Khao-teh-haeng 17, which was suscep-
tible to most of the previously identified races.
Blast resistance is generally "vertical"-a variety may be highly resistant to one
race of blast, but susceptible to others. We are incorporating broad spectrum resis-
tance into new lines so they will remain resistant in different regions and seasons. The
line IR1514A-E666, for example, was resistant to most races of blast during the 1973
epidemic of upland rice. Ten new races of blast were identified at IRRI during 1973,
bringing to 229 the total number of races identified.
We continued to coordinate the International Blast Nursery for the 11th year. We
distributed the seed of test materials to 26 countries. Local scientists are evaluating
them under their specific environmental and cultural conditions, and using the best
materials in their national breeding programs.
Searching for ways to cut time and land requirements for sheath blight resistance
screening, we tested three new methods: the seedling test, the detached flag leaf test,
and sheath inoculation. Varieties react distinctly to all methods, but results of the
three tests do not always agree. Unlike blast disease, no distinct physiological races of
sheath blight pathogens have been found. This may indicate that incorporation of
stable resistance to sheath blight will not be too complicated.

xviii IRRI ANNUAL REPORT FOR 1973

We initiated the International Sheath Blight Nursery this year by sending 60
varieties and lines with varying degrees of resistance to nine Asian countries. These
will be tested and the results shared among scientists in the cooperating countries.
We found very little variation in the physiological properties of Asian isolates of
the bacterial blight pathogen Xanthomonas oryzae, but virulence was found to vary
greatly. This is significant to scientists who are incorporating bacterial blight resis-
tance into new varieties.
We observed a particularly virulent strain of X. oryzae which breaks down the
resistance of IR20 and other resistant varieties in Isabela province, Philippines. We
are closely observing the new strain and have found two varieties (BJ1 and DZ192),
and their dwarf progenies, to be resistant to it.
Using the efficient "clipping technique" for inoculation, we screened all of the new
entries in the germ plasm bank, and all relevant breeding lines, for resistance to
bacterial blight in 1973.
We coordinated the International Bacterial Blight Nursery for the second year.
Material was tested at 18 locations in nine Asian countries.
A new screening technique allowed us to vastly expand our testing for resistance to
tungro, one of the most devastating virus diseases. We screened 11,000 rices in 1973.
We studied the epidemiology of tungro in farmers' fields and in greenhouses. By
learning more about the factors affecting the oubreak and spread of the disease, we
can determine better control methods and learn how to predict epidemics.
We observed tungro incidence in farmers' fields, and collected green leafhoppers
(the vector, or carrier, of tungro disease) at 26 sites in the Philippines. We caged green
leafhoppers with rice plants to determine which factors contribute to tungro infection.
We found that tungro incidence is proportional to the number of insect vectors. In
cage studies, increasing the number of insects from 15 to 600 per cage of 16 pots
increased the infection from less than 10 to 90 percent. Increasing the number of
diseased plants in the experiment increased the infected seedlings from 43 to 85 percent.
Prolonging the duration of caging increased the infection from 9 to 94 percent. The
nymphs spread the virus less efficiently than did the adults.
We found that an insect can infect about 10 to 12 seedlings with tungro during a
24-hour period. Although the percentage of infection rose with longer periods of
inoculation, the number of seedlings inoculated by an insect per unit of time decreased
with longer period of inoculation.
We developed a field screening technique for determining resistance to grassy stunt
virus. Resistant lines were entered in the replicated yield trials for the first time. The
proportion of our F2 populations with at least one parent resistant to grassy stunt has
risen from 10 percent in 1971 to 44 percent this year.
Insect resistance. Economic studies show that rice farmers generally use small
amounts of insecticides, and then only when damage is visible. This does not help if
the insect transmits a virus disease to the rice crops. And by the time a farmer
observes damage, it is often too late to control the insect.
But the success of IR20 showed that farmers quickly adopt varieties which are
resistant to these insect pests. Not only does insect resistance stabilize yields in
farmers' fields, it also lowers production costs. The newly released variety IR26, for
example, with its resistance to brown planthoppers, should help stabilize yields in
parts of India and the Philippines where this pest has devastated crops.
During 1973, 2,000 rice accessions and hybrids were screened for resistance to
green leafhoppers, brown planthoppers, and whitebacked planthoppers. We screened
1,500 accessions and lines for zigzag leafhoppers and found 44 to be resistant. Among

RESEARCH HIGHLIGHTS xix

the most resistant is the variety Ptb 21 from India, which is also resistant to green
leafhoppers and brown planthoppers.
Up to now, 12,000 accessions and lines have been screened for resistance to the rice
whorl maggot. Unfortunately, none were resistant, but a few moderately resistant
varieties are being crossed to try to increase the level of resistance to this pest. We
crossed varieties that are moderately resistant to striped borers and found that some
of the progeny are more resistant than either of the parents. We are investigating
several progenies which have the semidwarf plant type and are resistant to most of the
leafhopper and planthopper species.
Protein content. Rice is an important source of protein, supplying more than 50
percent of the total protein consumed in some countries. For that reason, even a
modest increase in protein levels in rice varieties would provide a significant nutri-
tional boost, especially for children, whose protein requirements are high. IRRI's
efforts to incorporate higher levels of protein into high-yielding varieties, if successful,
could affect the lives of millions.
In a cooperative study of the factors that affect protein content, statisticians,
agronomists, plant breeders, and chemists found that protein levels were affected
more by environmental factors than by genetic differences. Thus, yield-limiting
factors such as insects, diseases, or adverse soil conditions are likely to result in a
high protein content. Weather conditions and cultural practices, such as rate and time
of fertilizer application, water management, and weed control, also affect levels of
protein. These factors complicate selective breeding for higher protein.
We know, however, that there are real differences among varieties, which can best
be expressed in terms of "protein threshold," the level beyond which an increase in
yield is accompanied by a decrease in protein level. The experimental line IR480-5-9
yielded well and produced grains with 2 to 3 percent higher protein content than did
IR8 in farmers' fields in the Philippines. But it is susceptible to bacterial blight
disease. We are crossing IR480-5-9 to lines more resistant to insects and diseases.
During the 1973 growing seasons, we evaluated 424 lines for their protein content
and discarded 264 lines. Many crosses were made with lines resistant to the major
insects and diseases. Several such crosses with Ptb 18 and Oryza nivara have reached
advanced stages of testing in the disease and insect programs. The protein levels of
these lines appear promising.
We studied the nitrogen balance of weaning children I to 2 years old who were fed
diets of rice and fish. Substituting high protein rice in place of low protein rice in their
food raised the nitrogen balance of these children. This means that the added protein
was retained and used by the children.
Drought tolerance. Rice is grown in the tropics under conditions of normally high
rainfall. But the time and intensity of rainfall varies markedly, so rice is often subjected
to periods of severe moisture stress. A major objective of GEU is to develop rice
varieties which are tolerant to drought, and which will recuperate quickly when the
rains come.
Drought-tolerant varieties are most needed for upland conditions, where rice is
grown in unbunded fields that are prepared and seeded under dry conditions. They
depend entirely on rainfall for moisture. Upland rice farmers are among the poorest of
the world's subsistence farmers. Drought tolerance is also important for rainfed
lowland rice, the yields of which are often limited by unseasonal drought. Even
deep-water rice must have some drought tolerance because in some countries it is
direct seeded on land long before the high waters come.

xx IRRI ANNUAL REPORT FOR 1973

We developed a mass screening technique to evaluate field tolerance to drought at
different growth stages. Using this method of testing, hundreds of lines and varieties
can be screened under low moisture conditions in the dry seasons. We have identified
drought tolerant lines from traditional upland as well as lowland types. The semi-
dwarfs generally have low levels of drought tolerance, although they vary markedly in
this character.
Some varieties tolerant of drought in the field were found to have high proportions
of long, deep, and thick roots, which reach into the subsoil for water during moisture
stress.
Our agronomists have developed a technique by which a constant soil moisture
tension can be maintained in pots. With this technique, they screened 14 varieties and
lines for drought tolerance. The line IR1529-430-3 was most tolerant of soil moisture
stress.
We also tested 75 upland varieties and lines, including rices from Asia, Africa, and
Latin America, in farmers' fields in Batangas, Philippines. Rainfall was above
average and was well distributed during this trial. Twenty-four rices were identified as
promising. The highest yield was 6.6 t/ha from the experimental line IR3260-91-100.
In another test of upland varieties at the IRRI farm, soil moisture stress reduced the
plant height, tiller number, and dry matter production of all rices except the African
varieties E-425 and Moroberekan and the lowland semidwarf selections IR1661-1-
170, IR1531-86-2, IR1646-623-2, and IR1721-11-6. IR1646-623-2 was most tolerant of
drought. We found that late moisture stress reduced yields more than early stress.
Rices are probably more vulnerable to stress during the reproductive and ripening
stages.
We have crossed many diverse types to combine drought tolerance with superior
agronomic characteristics. Upland rices of intermediate plant height and moderately
high tillering ability might be more responsive to nitrogen than tall traditional types.
Through rigorous selection of hybrid progeny under upland conditions, we have
identified breeding lines that have good drought tolerance and improved tillering
ability. We are testing these lines in major upland rice areas in several countries.
Resistance to the movement of water vapor through the cuticle layer of the leaves of
rice is an important characteristic for drought tolerance. We measured the cuticular
resistance of the leaf surfaces of 35 rice varieties and found great variability in this
characteristic.
Studies of plant characters and grain yields in rainfed rice over three cropping
seasons lead us to believe that varieties can be developed which are capable of
adjusting their growth characteristics to fit existing land and water management
systems (upland, lowland, and moderately deep water). Such adaptability would
insure against total crop failure if rainfall is too low or too high for specific water and
land management systems.
Tolerance to injurious soils. IRRI scientists have used genetic variability to produce
lines that can tolerate insects, diseases, drought, and cold. We are now identifying
genetic materials that are adapted to injurious soil conditions such as salinity,
alkalinity, iron toxicity, phosphorus deficiency, and zinc deficiency. Iron deficiency is
a problem in many upland soils, and manganese and aluminum toxicities are common
problems in acid upland soils.
We are screening the world collection of rice germ plasm to identify varieties with
natural tolerance to these soil problems. We start by screening varieties which
originated in areas where the adverse soil conditions are common. Hopefully,

RESEARCH HIGHLIGHTS xxi

tolerance to injurious soils can be transferred into varieties of good grain quality, high
yield potential, and high insect and disease resistance.
Excess salt prevents rice from being grown on millions of hectares of low land in
deltas, estuaries, and coastal areas in the tropics. It also limits rice production in some
arid irrigated areas. In India alone, 7 million hectares of land are affected by salt.
Since projects to reclaim saline land are very expensive, high-yielding salt-tolerant
varieties are the most practical solution to the problem.
We have developed a technique to screen varieties for tolerance to salt. We raise
rice varieties in solution cultures and transplant them at 2 weeks of age into solid
cultures which contain 0.4 percent common salt. We are using this technique to
screen the world collection of varieties.
Alkalinity retards the growth of rice on several million hectares of irrigated soils in
the arid parts of India, Pakistan, Iran, and Egypt. These areas have abundant
sunshine, and far fewer disease and pest problems than do the humid tropics. But the
alkalinity problem must be solved, particularly if new land is to be brought into
production.
Alkalinity can be corrected-at high cost-by applying gypsum and following with
intensive irrigating and leaching. Developing varieties tolerant of this problem is a
simpler and cheaper alternative.
We developed a screening technique for alkalinity. It is similar to our salinity
screening method, but we transfer the plants into a solution containing 1.3 percent
sodium carbonate.
Zinc deficiency is the third most important nutritional problem of lowland rice.
Zinc deficiency is found in alkali soils, in some calcareous soils, and in continuously
wet soils. Varietal resistance offers the simplest solution. We have found in experi-
ments in Agusan del Norte, Philippines, that the varieties H4, IR5, and IR20 survived
on a zinc-deficient soil on which 29 other varieties died.
Iron toxicity is probably the most important single soil factor limiting rice yields on
vast acid-soil areas of the tropics, especially on acid sulfate soils. It severely retards
rice growth in mangrove swamps brought into production.
Lime can correct iron toxicity-but it is not economically feasible. The obvious
solution is to use improved varieties that tolerate iron toxicity.
Iron deficiency limits yields on upland soils, especially those of high pH. It can be
solved at prohibitive cost by submerging the soils or by applying iron compounds. We
hope to incorporate tolerance to iron deficiency into improved upland varieties. CAS
209, from Senegal, and the line IR1561-228-3 are good sources of resistance to iron
deficiency. We are searching for others.
Manganese and aluminum toxicities retard the growth of rice on acid upland soils.
Varieties such as Monolaya, from Colombia, and M1-48, from the Philippines,
tolerate excess manganese and aluminum.
Tolerance to deep water. In large areas of South and Southeast Asia, the water level
during the growing season is too deep for the new high-yielding semidwarf varieties.
In the so-called floating rice areas, the water depth ranges from 150 to 500 centimeters.
Millions of hectares of such rice are found in Bangladesh, Thailand, Indonesia, India,
Vietnam, and parts of Africa. The rice is planted before the heavy rains, in dry soil or
where there is little standing water. As the monsoon rains raise the water level, the
stems rapidly elongate, keeping the panicles above water. Floating rice is sometimes
harvested from boats. In areas where the water recedes before harvest, a tangled mass
of stems and curving shoots is left behind. Floating rices yield somewhat like tradi-
tional unimproved lowland rices.

xxii IRRI ANNUAL REPORT FOR 1973

Floating rice culture has not been thoroughly studied by scientists. Varietal
improvement has been limited to selection of the better existing varieties.
We hope to increase and stabilize the grain yields of floating rice. First, we must
identify the factors which limit yields. We are screening and classifying germ plasm of
floating rice and selecting the most appropriate materials for crossing work.
We plan to establish an international nursery program to test promising genetic
material under different cultural and environmental conditions.
In an even larger area than that occupied by floating rice, the annual flood waters
commonly reach up to 150 cm in depth. The varieties used are tall indica types and
not necessarily floating rices. A genetic evaluation program similar to that for floating
rice is being undertaken to improve the yielding ability of these rice varieties. Im-
proved varieties may be semidwarfs which have the ability to elongate as flood waters
rise, to prevent the plants from being submerged. But in years when the water level is
low, the plants will remain short, providing a better plant type.
Crops are often completely submerged by unpredictable floods in vast rice areas
where water control is poor. Submergence may last from 1 to 30 days at different
growth stages. We hope to develop flood-tolerant varieties which can withstand such
conditions, and will yield well. Varieties screened in the GEU program for deep-water
rice will provide breeding material for the flood tolerance program.
Cold tolerance. Modern rices have not been adopted in subtemperate and in many
mountainous areas because of poor performance when grown under low temperatures.
In some irrigated valleys, cold irrigation water from the surrounding uplands has
limited the new rices.
Through our cold tolerance program, we are identifying rices that grow well under
lower-than-normal temperatures. We hope to incorporate this ability into high-
yielding varieties.
IRRI scientists have developed a technique to identify tolerance to cold water at the
seedling stage and are determining other methods of screening at later growth stages.
We will screen materials under controlled environmental conditions in the phytotron.
An international cold tolerance nursery will be established once we have identified
enough promising lines.
Insect control and management. While host resistance is being sought for the major
insect pests, the use of pesticides will likely continue to be an important component
of an integrated pest control program. Our objective in working with these chemicals
is to find inexpensive and effective means of complementing control through host
resistance.
We evaluated different insecticides and application methods to learn how farmers
can maximize returns on insecticidal investments.
We found that insecticides, when packaged in capsules and placed in the root zones,
are more readily available to the plants by systemic effect. Inserting the insecticide
capsules below the soil surface protects them from heat, sunshine, volatilization, and
drainage with overflowing water (fig. 6).
We analyzed plant tissues and found that 10 times more insecticide was absorbed by
plants when applied to the root zones than when applied to the soil surface or incor-
porated into the top soil. Even at 40 days after treatment, twice as much insecticide
was found in plants which received the root-zone application as in plants which
received the other treatments. Root zone application is more effective and lasts longer
than paddy water application.
In biological control studies, we found that a predator organism (Cyrtorhinus
lividipennis) can kill an average of 0.6 brown planthopper nymphs per day, or 50 green

RESEARCH HIGHLIGHTS xxiii

2.5cm
-I

Capsule

6. Packaging insecticides in capsules and placing them in
the rice root zones protects the insecticides and makes them
more readily available to the plants.

leafhopper nymphs per day, for at least 4 consecutive days. The predator prefers to
prey on nymphs rather than on adults, and prefers green leafhoppers to brown
planthoppers.
We studied "integrated pest control" or the combination of host plant resistance
and insecticide treatments. Frequent applications of insecticides often increased
yields, but were not usually profitable. In most cases, we found that IR20 could be
grown more profitably with no insecticide treatments. In areas where insect and virus
problems were minor, even susceptible IR22 could be grown profitably without
insecticide application. But in areas where the brown planthopper was a serious pest,
susceptible varieties yielded only moderately, even with frequent applications of
insecticides.
In the laboratory and in farmers' fields, we identified insecticides that are effective
against green leafhoppers, brown planthoppers, and striped borers. Thoroughly
spraying the lower halves of rice plants, where brown planthoppers live, with per-
thane, chlordimeform, and bux provided long lasting control of the pest. For larger
farms, agricultural engineers have designed a 12-meter boom spray with drop nozzles
which can be attached to a power sprayer.
We are studying the economic thresholds for insect control. Insect damage by
green leafhoppers and brown planthopper nymphs caged on plants was found to be

xxiv IRRIANNUAL REPORT FOR 1973

significant when the plants were young, and at the booting-to-flowering stages. Plants
can usually tolerate 5 to 10 nymphs per tiller for 2 weeks without yield loss. We think
that certain densities of young nymphs at different plant stages may be simple
economic thresholds for field control of brown planthoppers.
Weed control. We put together herbicide trials and distributed material for 142
experiments in 15 Asian countries in 1973. The experiments were conducted under
transplanted, direct-seeded, flooded, and upland conditions. Herbicides for 15 more
trials were sent to the West Africa Rice Development Association (WARDA).
Based on the results from these cooperative studies, several new herbicides are now
being marketed in Asia, including formulations and derivatives of 2,4-D and MCPA,
butachlor, and benthiocarb. Competition helps keep prices low.
With pressures on the land increasing, farmers need to prepare land in a shorter
time for intensive rice or multiple crops cultivation. Zero-tillage and minimum tillage
are methods of doing this.
Using herbicides for weed control, we investigated zero tillage for growing direct-
seeded rice under flooded conditions. Plots treated with glyphosate followed by
paraquat, and never tilled, yielded as much as those plowed once and harrowed twice.
Scirpus maritimus, a fast-growing sedge, wasn't much of a problem a few years ago.
But better control of annual weeds and the introduction of irrigation water have
helped to spread the perennial sedge. Scirpus has underground tubers that are left in
the ground when a farmer kills the topgrowth. Thus, ordinary cultivation or herbicides
may allow the weed population to shift until Scirpus predominates.
Plant physiologists are studying different aspects of the growth of Scirpus. When we
know the growth characteristics of the plant, we can find better ways to control it. Our
agronomists have identified two herbicides (bentazon and silvex) that control Scirpus.
We have found in experiments in farmers' fields that intermediate-statured rices
may compete with weeds better than semidwarfs. This is one reason we are developing
some varieties intermediate in height as well as semidwarfs.
Water management. Our program in water management focuses on water measure-
ment and control within irrigation systems, since farmers appear to allocate water
fairly well on their farms, where they have control of it. We are looking at two
competing indices of water management, that of efficient water use, and that of
minimal moisture stress in irrigated areas.
Field research carried out jointly with the Philippine National Irrigation Adminis-
tration (NIA), the University of the Philippines at Los Baiios College of Agriculture,
and IRRI showed that yield loss due to stress tends to be low in fields located near the
beginnings of distribution canals, but increases markedly in irrigated fields near the
ends of the canals. Efficiency of water use tends to be much lower in areas near the
beginning than in areas located further along the canal. This indicates a tendency for
farmers near the beginnings of canals to overirrigate, and for those in the lower reaches
of major canals to have insufficient water. The date of transplanting is often delayed as
much as a month in the lower reaches.
In a pilot study in cooperation with the NIA, we are exploring different ways of
managing a 5,000-ha system to equalize the distribution and achieve greater overall
production of rice.
Nitrogen fixation and fertilizer utilization. Nitrogen is perhaps the most limiting
plant nutrient for rice production. Without adequate supplies of nitrogen, high grain
yields are impossible. The worldwide production of nitrogen fertilizer is far less than
the demand, so prices are skyrocketing. This development is especially threatening to
agricultural production in the poorest countries.

RESEARCH HIGHLIGHTS xxv

Ironically, the air around us holds an unlimited supply of nitrogen. IRRI scientists
are searching for ways to make more of this atmospheric nitrogen available to plants,
decreasing the farmers' dependence on costly fertilizers.
IRRI researchers have discovered that atmospheric nitrogen can be "fixed" in
paddy soils in a form that rice plants can use. The equivalent of 60 kilograms per
hectare of nitrogen has been fixed in some experiments. This may explain how rice has
been grown continually on the same paddy fields, without fertilization, for hundreds
of years.
IRRI scientists are studying the mechanism for this fixation. We know the rice plant
has a mechanism for transporting atmospheric nitrogen to the root zone. Bacteria
surrounding the roots derive part of their energy from organic exudates from the roots
and use this energy to convert the gaseous nitrogen into combined forms which the
plant can use.
We have observed only low rates of nitrogen fixation in upland soils. This indicates
that the bacteria fix significant amounts of nitrogen only when oxygen concentration
in the root zone is low, as in submerged soils.
We hope to find ways to increase the efficiency of nitrogen fixation, and to deter-
mine the conditions under which the plant best uses the fixed nitrogen. We are
screening rice varieties to determine their relative nitrogen-fixing capacities. Perhaps
in the future, rice varieties can be selected which encourage high rates of nitrogen
fixation and which use fertilizer and soil nitrogen more efficiently.
In the laboratory, we have found that rice plants fix higher levels of nitrogen when
phosphorus and potassium are added. Also, in one field experiment at IRRI, signifi-
cant yield increases were obtained from adding either phosphorus or potassium
without nitrogen. Such nutritional response to phosphorus or potassium is not com-
mon at IRRI, suggesting that the beneficial effects of adding these two nutrients may
have been due to their indirect influence on nitrogen fixation.
We have also found that leaving rice straw in the field after harvest accumulates a
substantial amount of nutrients. Using this practice, we produced yields of as high as
5 t/ha from Philippine lowland soils without fertilizers.
Because of the increased emphasis on upland rice, we are searching for more
efficient methods of applying different forms of nitrogen under poor water manage-
ment. In soils that are continually flooded at 5 cm, or that are intermittently irrigated,
we found that readily soluble sources of nitrogen produced higher yields when
applied as three split doses rather than when all the fertilizer was applied as basal
before planting. Slowly available sulfur-coated urea gave slightly higher yields when
applied as a single basal treatment. In farmers' fields in Nueva Ecija, Philippines, we
also found that ammonium sulfate and ordinary urea produced higher grain yields
when applied in split doses. But with sulfur-coated urea, yields were higher when the
fertilizer was applied as one basal application.
Fertilizer is relatively expensive in Asia, and labor for applying it is relatively cheap.
So applying ordinary fertilizers as split doses has more merit than applying slow-
release fertilizers as one dose, even though the split dose requires more labor. Slow-
release fertilizers may be better, however, when water control is inadequate and the
soil is alternately wet and dry.
Environmental influences. The rice plant is influenced markedly by the environment
in which it is grown. This environment includes factors such as solar radiation,
temperature, humidity, soil moisture supply, and the supply of carbon dioxide in the
atmosphere.

xxvi IRRI ANNUAL REPORT FOR 1973

We determined the effects of climatic variables on yields and components which
affect yields by planting an early maturing rice line (IR747-B2-6) every 2 weeks, a
total of 26 crops in one year. The yields varied from 4.6 to 7.1 t/ha and were related to
the season of the year during which the crop grew.
A combination of high solar radiation and low temperature in the period 25 days
before flowering markedly increased yields, primarily through an increase in numbers
of grain per square meter. This characteristic was by far the most important yield
component. It accounted for 74 percent of the measured yield variation while percent
of filled grains and weight per unit of grain accounted for the remainder of the
measured variation. Disease and insect control was maintained by the use of pesticides
in this trial.
We studied the relationship between solar radiation, leaf resistance (combined
resistance of stomates and cuticle), and soil moisture stress (drought). Rice plants
grown under flooded conditions had low leaf resistance, suggesting that stomates
remained open even during the daytime. Plants grown under soil moisture stresses,
similar to those found in upland rice conditions, had high leaf resistances, especially
in the afternoons on sunny days. Increasing the light intensity actually reduced the
rates of photosynthesis for plants grown under moisture stress. Such photosynthetic
restriction during periods of drought suggests that strong sunlight may be wasted
under water stress. Upland rice culture under partially shaded conditions (such as
under coconut trees) merits further study.
New phytotron. The Australian government has constructed a simulated climate
control facility (phytotron) at IRRI to strengthen research on the response of the rice
plant to environmental changes (fig. 7).
The environment can be controlled and manipulated in the phytotron's growth
rooms. Scientists will be able to simulate many of the climatic conditions under which
rice grows in different regions, and can measure how the rice plant responds to these
conditions. Temperature, daylength, and humidity can be controlled in the phytotron's
six glasshouse rooms, 10 artificially lighted growth cabinets, and eight naturally
lighted growth cabinets. Light intensity can also be controlled in the artificially
lighted cabinets.

7. IRRI's new phytotron, a simulated climate control facility, will strengthen research on the response of
the rice plant to environmental changes.

RESEARCH HIGHLIGHTS xxvii

With the phytotron, scientists can measure the effects of individual climatic
factors separately from those of closely related factors. Many experiments can be
repeated at any time of the year. The phytotron will go into operation in 1974.
Machinery development and economics. Farm machines are usually designed for
large operations in the labor-scarce developed nations; they are often technically or
economically unsuited for small-scale farmers in the rice-producing countries.
Simple inexpensive machinery is being developed at IRRI for these smaller farmers.
The machinery is designed not to replace but to increase the productivity of labor. The
designs are released free to manufacturers who want to locally produce IRRI equip-
ment. This saves foreign exchange, creates employment, and builds local industry.
Most popular among the IRRI machines is the 5-hp to 7-hp power tiller. It is being
built in small machine shops from locally available materials and sold at about half
the price of a comparable imported model.
Sales of the power tiller are impressive. More than 3,000 were sold in the Philippines
during 1973-about 70 percent of the total power tiller sales for the country. The
machine has been tested in a dozen countries and is being produced commercially in
Sri Lanka and Thailand. This year, we redesigned certain components of the tiller, and
adapted several attachments to broaden its utility.
We completed field testing of the axial flow multicrop thresher in 1973. This versa-
tile machine can thresh not only rice, but also other crops. It is being produced in the
Philippines, Pakistan, Sri Lanka, and Thailand.
We modified the design of our PTO-driven thresher, and neared completion of a
6-row stripper harvester. A wooden bin has been designed to reduce initial investment
costs of the 1-ton batch dryer. We are evaluating a modified Engleberg steel-huller
mill. Tests indicate that recovery of both total rice and head rice (unbroken grain) can
be significantly increased through minor changes in the machine.
Because chemical herbicides are becoming more expensive, we designed a machine
to directly apply non-selective herbicides. It seems to perform well in row crops.
Economists are studying how the production of IRRI designs affects employment.
We found that employment had increased by 96 percent at five firms when they began
to manufacture IRRI machinery. Most of the firms previously had excess utilization
capacity; producing the IRRI machines increased the use of their existing plants and
equipment by 20 to 30 percent.
Many more jobs are created when these firms sub-contract the production of
assemblies and component parts to other small industries. The five firms subcontrac-
ted work for the production of IRRI equipment to 45 other firms.
To determine how farm machinery is being used, and to determine the effects of
mechanization on labor and economics, we interviewed 142 large tractor operators in
Nueva Ecija, Philippines. The tractors are used 60 to 70 percent of the time for
contract operations, principally land preparation. Use is seasonal. If suitable imple-
ments and accessories are made available at reasonable costs, we see considerable
potential for increasing their use.
Grain handling and processing. Rice production doesn't end when the grain ripens.
The crop must be harvested, dried, and milled before reaching the consumer. We are
searching for ways to help farmers minimize grain losses during these phases.
We analyzed grain losses during wet and dry seasons on 50 farms in Central Luzon,
Philippines. We found that about 3 percent of the grain is lost during harvest, and that
these field losses are affected by time and season of harvest, variety, and the availability
of irrigation water. Harvesting grain at high moisture level (above 20 percent) reduces
shattering and cuts field losses to less than 1 percent.

xxviii IRRI ANNUAL REPORT FOR 1973

We compared solar and mechanical drying by measuring both total rice recovered
after harvest and head rice recovered after milling. We found that harvesting rice at
high moisture levels and drying it mechanically decreases field losses at harvest,
lowers milling losses, and gives milled rice of better quality.
Grain quality. Gel consistency indicates the rates at which cooked rice hardens.
Low gel consistency is preferred over high, even for waxy rices.
We developed a rapid and simple test to measure the gel consistencies of different
rices. This test is designed to complement the amylose test to help us select grain types
that consumers will prefer.
Constraints to rice yields. Because yields in farmers' fields have remained far lower
than those in experiment station plots, we have focused several studies on farm level
constraints to high yields.
We coordinated a regional project in Pakistan, India, Malaysia, Thailand, the
Philippines, and Indonesia to study the changes in production, farm income, and
farm employment that have followed the modern rice varieties, and to determine why
the technology has been readily accepted in some areas, but not in others.
Twenty-five social scientists in the six countries cooperated with IRRI on the study.
In 30 Asian villages where modern rice varieties have been well accepted, we found
that farmers grow these varieties more widely in the dry than in the wet seasons. The
farmers consider pests and diseases the most serious constraints to high yields for
modern varieties. In some countries, government policies have discouraged accep-
tance of the new technology.
Suitable modern varieties were not available for some villages, particularly those
where deep flooding is common. In villages where substantial land was planted to
crops other than rice, yields were significantly higher than in villages where only
lowland rice was grown.
About 50 percent of the farmers reported that after adopting the new technology,
they hired more labor and their own standards of living increased. About 15 percent
reported decreases in hired labor and lower standards of living after the new tech-
nology was introduced.
We developed a new field plot technique to identify and quantify the constraints to
yields in farmers' fields. We monitored the practices that each farmer followed and
measured the rice yield on each sample farm. Actual yields are compared with the
potential yields at the same location when recommended practices are applied, and
with yields at various levels of intermediate technology. We applied the technique for
three crop seasons in 15 farms in Laguna province, Philippines.
Pest and disease control was found to be the most crucial constraint, consistently
reducing farmers' yields by about 1.2 t/ha, irrespective of crop season (fig. 8). In the
dry season, water was found to be the next limiting factor, reducing yields by 0.9 t/ha;
followed by nitrogen fertilization, 0.7 t/ha; weed control, 0.3 t/ha; and seedling
management, 0.3 t/ha. During the wet season, weed control was relatively more
important than factors other than insect control.
Using a somewhat different technique, we studied how factors both within and
beyond the control of farmers affected yield levels in two irrigated villages and one
rainfed village over 3 years in Nueva Ecija province, Central Luzon, Philippines.
We determined relationships among managerial factors, such as fertilizer appli-
cation and cultural practices, which are within the farmer's direct control; environ-
mental factors, such as solar radiation and soil texture, which are completely outside
the farmer's control; and factors such as moisture stress, which are beyond the direct
control of the farmer, but which may be potentially controllable by group action or

RESEARCH HIGHLIGHTS xxix

Seedling -
9% \ Insects and
diseases
35% \=siiii
Weed 9-%o 34 t/ha

Nitrogen Water
21% 26%

RECOMMENDED FARMERS'
PRACTICES PRACTICES
73 t/ha 3.9 t/ha
/~ DRY SEASON
Insects and DRY-S-- --
S diseases 1--

N i t r o g e n',ERI C
6%

RECOMMENDED FARMERS'
PRACTICES PRACTICES
5.0 t/ha 3.3 t/ha
WET SEASON

8. Differences between yields when farmers follow their usual practices,
and when they follow IRRI recommendations. Factors which constrain
yields in farmers' fields are shown in the circles(3 crop seasons, 15 farms,
Laguna province, Philippines).

investment by society (for example, although an individual farmer may have no
influence over moisture stress, irrigation might be extended to the affected area).
We found that, although good management practices often help explain why some
farms and villages have higher yields than othersictors which are beyond the direct
control of individual farmers, such as soil properties and availability of irrigation,
often influenced yield differences to a much greater extent.
Among villages with similar physical resources, such as the two irrigated villages,
managerial factors often accounted for most yield differences. But management
factors accounted for only a third to a half of the yield differences between the
irrigated and the rainfed villages.
We found that adoption of a package of management practices increased yields by
at least halfa ton per hectare in the irrigated villages, but did not increase yields under
conditions of poor environment.
In an aggregate study of the factors which restrict yields on a national basis in the
Philippines, we found that lack of water control is the single biggest yield constraint,
responsible for about 25 percent of the differences between potential and actual
yields (fig. 9). Seasonal factors, such as available solar radiation, account for another
20 percent of the yield differences. Economic factors, including risk, account for 15
percent of the differences. Year-to-year variability in weather conditions and in pests
and disease damage account for 20 percent of the differences, and the lack of available
inputs and non-adoption of new technology accounted for 15 percent.
Many of these constraints can be reduced or manipulated by appropriate financial
investments, policy changes, research, and selective breeding. The construction of

xxx IRRI ANNUAL REPORT FOR 1973

Yield (t/ho)

variations

86-
6 CONSTRAINTS
TO
HIGH
Water control RICE
YIELDS
4
Risk, cost -

2

Potential Actual
9. Lack of water appears to be the single most important
constraint to high yields in a preliminary aggregate study on
a national basis in the Philippines.
irrigation and drainage systems, and modification of their management, can alleviate
poor water control, for example. Policy measures to insure available credit and favor-
able prices can ease economic constraints. Fertilizer inputs might be reduced if
varieties or farming systems can be developed which encourage the microbial
fixation of atmospheric nitrogen in the soil. Year-to-year variability due to weather
conditions can be eased by developing rices which are tolerant to drought and
submergence, or which yield well under low solar radiation conditions of the monsoon
seasons. Insect and disease damage can be reduced by incorporating higher levels of
pest resistance into modern varieties.
Pilot extension program. We cooperated with Philippine agricultural agencies in
developing an extension methodology for taking rice technology to the farm level
which may be applied in other countries. The methodology was tested in the Philip-
pine government's successful "Masagana 99" program ("Masagana" means "bounti-
ful harvest" and "99" refers to the goal of 99 cavans, about 4.4 tons, per hectare).
The technology included the use of a package of practices: improved varieties;
proper use of fertilizers, herbicides, and insecticides; supervised farm credit; fixed
minimum support prices; massive promotional campaigns; farmers' field days;
training, incentives, and mobility for technicians; and a trouble-shooting committee
to identify and remove production constraints.
The program was very successful. Production levels appear to be near record in
spite of unanticipated shortages of both fertilizers and pesticides due to the energy
crisis.
The governments of Bangladesh and Thailand are considering the initiation of
similar campaign programs to rapidly intensify production. Through our cooperative
projects, we hope to encourage other countries to use similar methods to stimulate the
rapid and widespread adoption of modern rice technology.

RESEARCH HIGHLIGHTS xxxi

Rice cropping systems. IRRI scientists have demonstrated that rainfed lowland rice
which is seeded directly on non-puddled soil at the beginning of the rainy season rather
than transplanted during the middle of the rainy season takes advantage of early
rainfall and may allow an extra crop of rice to be grown.
Although the rains begin in May in Central Luzon, Philippines, farmers seldom
have enough water to plow and puddle the soils until July or August. To have seed-
lings of the proper age ready for transplanting, farmers must accurately forecast when
sufficient water will be available and start their seedbeds 3 to 4 weeks in advance. By
the time crops are transplanted, often in August, seedlings may have passed the
optimum age.
We have found that yields are similar in direct-seeded rainfed and transplanted-
irrigated rice. Tests show that herbicides will control weeds in crops which are direct
seeded in dry or moist soils.
Rice production specialists established experimental direct-seeded plots on farmers'
fields at nine different sites in Central Luzon. The first crops of early maturing lines
were sown in early May, before the heavy rains began. These crops were harvested in
mid-August-before the last 40 percent of the surrounding farmers had transplanted
their first crops (fig. 10). Seedbeds for the second crops had been prepared about 3
weeks earlier, and seedlings were transplanted immediately after harvest. Farmers
were harvesting this second crop at the same time that local farmers using traditional
crop cultures were harvesting their first (and only) crop.
We are now developing improved technology for direct seeding of rice.
Multiple cropping-growing two, four, even five crops a year on the same ground
instead of only one-is another means of intensifying production.
Modern rice varieties mature a month or more earlier than traditional rices, leaving
enough time and soil moisture to grow other crops. Residual fertilizer left in the
ground after rice harvest can be converted into more food, rather than be wasted.

Jon Feb Mor Apr May Jun Jul Aug Sep Oct Nov Dec
DIRECT SEEDING HARVESTING
FIRST CROP FIRST CROP

TRANSPLANTING HARVESTING
SECOND CROP SECONDCROP
NORMAL NORMAL
TRANSPLANTING HARVESTING

60_ Bulocan
(27-year overage)

"0
E

S2 Water accumulation

Jon Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

10. Early maturing rice lines were direct-seeded in farmers' fields in early May, before the heavy rains
began, in Bulacan, Central Luzon, Philippines. Some of these crops were harvested before surrounding
farmers, using regular cropping systems, had transplanted. Second crops were harvested at about the
same time the local farmers were harvesting their first and only crops.

xxxii IRRI ANNUAL REPORT FOR 1973

Alternate crops will use to the fullest advantage the long and warm growing season of
the tropics.
Multiple cropping itself is not new. Farmers have grown other crops with or follow-
ing rice for a thousand years. But the need to intensify cropping is far greater today
than ever before.
We are studying the biological potentials of different cropping systems. We hope to
develop intensive farming schemes that are slanted to the needs of small-scale
farmers.
We have found that the traditional practice of "intercropping" (growing two
compatible crops such as corn and upland rice simultaneously in alternate rows) is
highly suited to situations of limited land and surplus labor. Intercropping increases
the productivity of the land by a third-a hectare of intercropped corn and upland
rice produces as much as one and a third hectares of corn and upland rice planted
separately. Intercropping uses inputs more efficiently.
In fact, adding nitrogen fertilizer to an intercrop combination of corn and rice gave
a much higher return on investment than did adding nitrogen to either corn alone or
rice alone.
Intercropping corn and mung decreases the need for weeding and modifies weed
response to fertilizer. Because the dense canopies intercept sunlight, intercropping
provides a biological system of weed management. The canopies also prevent shifts
in weed population to more troublesome grasses and sedges.
We are finding that certain traditional farming practices, including mixed cropping,
help the small farmer control insects in his crops-even though he may not know why.
We learned, for example, that intercropping peanut with corn lowers corn borer
infestation apparently because the peanut crop is a natural habitat for a spider which
preys on the corn borers.
Training. A hundred and twenty-six graduate students and production trainees
from rice-growing countries work with IRRI scientists in the fields, greenhouses,
laboratories, and classrooms.
The individuals selected for training are staff members of government agencies and
institutions involved in research and extension in rice-producing countries. The long-
range objectives of the training program are to improve the technical proficiency of
national research and extension staffs and to encourage multi-disciplinary research
and production programs.
Ninety-two of the participants were in research-oriented programs. Many studied
for master's degrees at the University of the Philippines at Los Bafios, taking their
course work at the University and conducting their thesis research at IRRI. Doctoral
candidates and post-doctoral fellows conducted research in problem areas that
pertained to their countries.
Thirty persons participated in rice production training programs. Most were
extension and education specialists who were trained not only in crop production but
also in how to run similar training courses when they return home. They studied the
theories of agriculture and applied research in the classroom, but they spent half their
time in the fields applying the theories and learning every step of rice production.
International programs. Because the largest areas of rice production are outside the
Philippines, we continued to stress our responsibilities and opportunities to work
with national rice research organizations (fig. 11). We must help strengthen national
research capabilities if we are to be influential in helping rice-producing countries
develop superior technologies suited to their local conditions.
IRRI coordinates several international testing programs. The types of nurseries and

RESEARCH HIGHLIGHTS xxxiii

UNITED STATES BANGAF
OF AMPERICA PAKISTAN 9N600000 h
740,000 ha 1,500,000 ha 2,700,000 h

EUROPE URMA
320,000 0,. 5,0o0,00 ha
-- __ I -_1 -ISOUTH KOREA
INDIA 1,200,000 ha
37,000,000 ha TAIWAN
BRAZIL AFRKA LS 0,000 h
5,200,00oh ,0000 h THAILAND NORTH Too ,oo ho
6,8000,0 h VIETNAM

S,,800,000 h
REST OF LATIN AMERICA
1,300,000 ha UPPINES

MALAYSIA- -
700,000 h. SOUTH
SSRILANKA VIETNAM
I-1600,000 ho 2;500,000 ho

INDONESIA
-40,000 hectares 8,200,000 ho INA ST
I oooo AUSTRALIA
40,000 ha

11. The largest areas of the world's rice land are outside the Philippines. IRRI cooperates and works
with many of these national rice research organizations to help them develop better technologies suited to
their local rice-growing conditions.

the numbers of test locations increased in 1973. The nurseries now include: the
International Blast Nursery; the International Sheath Blight Nursery; the Inter-
national Bacterial Blight Nursery; and the International Rice Yield Nursery (fig. 12).
In addition, herbicide trials were distributed to 15 Asian countries, and to the West
Africa Rice Development Association (WARDA). We plan to expand our inter-
national testing systems.
IRRI-designed machines were evaluated in India, Indonesia, Korea, Malaysia,
Pakistan, Philippines, Sri Lanka, Taiwan, Thailand, and Vietnam.
IRRI cooperates in regional rice research with the International Institute of
Tropical Agriculture (IITA) and WARDA, in Africa, and with the Centro Inter-
nacional de Agricultura Tropical (CIAT) in South America.
A third of our staff is with our "outreach projects" in Bangladesh, Egypt, India,
Indonesia, Philippines, Sri Lanka, and South Vietnam. We are participating, at the
request of the host governments, to strengthen and accelerate the national rice
research programs. The scientists live and work in the countries as members of local
scientific teams. We supplied improved genetic material and helped train rice scien-
tists. Our scientists at Los Bafios serve as "back stop" subject matter specialists when
needed.
In Bangladesh, we are cooperating with the new Bangladesh Rice Research
Institute (BRRI), under a Ford Foundation contract.
IRRI scientists worked with Egyptian scientists to evaluate the potential of
growing IRRI selections with long and slender grains in Egypt, where past production
has been confined to japonica varieties with short and bold grains. This project was
sponsored by Ford Foundation.

xxxiv IRRI ANNUAL REPORT FOR 1973

INTERNATIONAL TESTING PROGRAM

International Basic Screening Nurseries
Adverse soil
Diseases Insects and weather
Blast Green leafhopper Injurious soils
Bacterial blight Brown planthopper Cold tolerance
Tungro Stem borer Upland
Sheath blight Gall midge Deep water

12. IRRI now coordinates international testing programs for blast,
sheath blight, and bacterial blight diseases, and an international rice
yield nursery. We hope to expand our international testing system to
include other diseases, insects, and adverse conditions.

We cooperate with India through the All-India Coordinated Rice Improvement
Project, through which India directs her resources to serve a variety of environmental
and cultural conditions. The U.S. Agency for International Development (USAID)
contract, which had supported IRRI scientists in India, was phased out in 1973. A
Rockefeller Foundation scientist continues to be the IRRI representative in India.
The chief objective of IRRI's four projects in Indonesia is to develop a coordinated
rice research program which uses limited manpower and facilities more efficiently.
The projects are sponsored by the Ford Foundation, USAID, the World Bank, and
the Dutch government.
An IRRI crop production specialist works with the Philippine government under
a USAID contract to help incorporate research results from IRRI and other agencies
into national production programs.
We have two cooperative projects in Sri Lanka: one on production aspects of rice
and multiple cropping, and another on rice processing.
Two IRRI scientists work in South Vietnam under a USAID contract, helping
local scientists conduct varietal yield trials, fertilizer trials, and herbicide and insecti-
cide screening trials at four locations.
IRRI's annual rice research conference provides a forum for scientists to discuss
new research findings and ideas. Seventy-five rice scientists from 20 countries attended
the International Rice Research Conference in 1973. They agreed on the need for more
cooperative nurseries to identify broad-spectrum resistance to diseases and insects,
and for more field trials to screen promising genetic lines and to evaluate herbicides.
Seventy-eight participants met at IRRI for a conference on rice machinery in 1973,
sponsored jointly by IRRI and the United Nations Industrial Development Organi-

RESEARCH HIGHLIGHTS xxxv

zation (UNIDO). The participants explored ways to promote local manufacture of
machinery for rice production in the developing countries.

FINANCES During 1973, the institute received cash grants amounting to $4,265,105.
The Ford Foundation gave $1,549,097. Of this amount $750,000 was toward the
core operating and capital expenditures of the institute. The remainder was in support
of the rice research and development programs in four countries: Sri Lanka-
$162,500 as part of a 2-year grant for the rice production and multiple cropping
project and another $142,000 as part of a 2-year grant for the project on rice proces-
sing and marketing; Indonesia-$90,200 which is part of a 2-year grant for an acceler-
ated rice research program; Egypt-$38,000 which is part of a 2-year grant for the
services of a project specialist with the Arid Lands Agricultural Program in the
Middle East; Bangladesh-$255,600 which is part of a 21-year grant to provide
support for the Bangladesh Rice Research Institute, and another $105,000 which is
part of a 2-year grant to provide support to the Bangladesh Rice Research Institute;
India-$5,797 which is part of a 13-month grant for the services of a plant pathologist.
The Rockefeller Foundation contributed $672,535 during 1973. This amount
included $620,000 for the core operating and capital expenditure needs of the institute,
of which $500,888 was received in cash and the balance represented the value of the
foundation's manpower contribution to the institute. The Rockefeller Foundation
released $24,250 as part of a 3-year grant in support of the experimental program to
identify and demonstrate techniques for increasing the productivity of disadvantaged
Asian rice farmers, and $28,285 as part of a grant for the collection of the world's
germ plasm of rice.
From various grants, the U.S. Agency for International Development released a
total of $1,170,364 in 1973. The institute received $554,622 during the year for its
core operating and capital expenditures and $209,094 in support of a project entitled
"Research on Farm and Equipment Power Requirements for the Production of Rice
and Associated Food Crops in the Far East and South Asia." Since 1967 a contract
between the institute and USAID has supported a project for the acceleration of rice
research and training programs in India. During the year, the institute received
$104,501 for this project. Since 1971, a contract with USAID has supported a project
to help the government of Vietnam to accelerate rice research for a 3-year period with
a budget of $310,000 in addition to a budget of VN$12,200,000. In 1973, $54,823
was reimbursed to the institute. Since February, 1972, a contract between the institute
and USAID has supported the accelerated development and utilization of improved
technology in agriculture in Indonesia with a budget of $472,359 in addition to a
budget of Rp. 424,582,000 which is managed by the USAID mission in Djakarta for a
period of 2 years. In 1973, $190,892 was reimbursed to the institute. Since July, 1972,
a contract between the institute and USAID supported an intensified crop production
and extension program in the Philippines for 2 years with a budget of $85,000 in
addition to a budget of P92,400 which is managed by the USAID mission in Manila.
In 1973, $35,096 was released to the institute. USAID contributed toward the training
program of the institute by supporting scholars from various countries where USAID
has active programs. The institute received $17,777 for this purpose this year. The
USAID mission in Bangladesh provided $26,000 to finance the training of staff from
the Bangladesh Rice Research Institute to be carried out at IRRI and at other
institutions selected by IRRI. During 1973, $3,559 was released to IRRI.
The Overseas Development Administration of the United Kingdom gave $338,897
toward the support of the institute's plant breeding department.

xxxvi IRRI ANNUAL REPORT FOR 1973

The International Development Research Centre of Canada gave $111,085. As part
of a 2-year grant to the institute for the multiple cropping research in the Philippines in
cooperation with the University of the Philippines at Los Bafios, IDRC released
$98,275 in 1973. The centre made another grant to the institute for research on
changes in rice farming in Asia and released $12,810 to the institute in 1973 for this
purpose.
The Japanese government gave $228,780 in 1973 toward the training program of
the institute, toward the purchase of equipment required for research activities of the
institute, and toward the support of the institute's plant physiology department.
The International Development Association gave $120,000 in 1973 toward the core
operating and capital expenditures of the institute.
The government of Indonesia, using a World Bank loan, released $32,631 as part of
a 5-year contract toward the research facilities of the Sukamandi Branch of the
Central Research Institute for Agriculture (CRIA) and toward scientific and other
assistance to this new branch.
In 1967 the institute entered into a cost-reimbursement contract with the U.S.
National Institutes of Health to study ways to increase the protein and essential
amino acids of the rice grain through plant breeding. During 1973, $34,374 was
reimbursed to the institute.
The Australian government gave $6,375 toward a short-term training program of
the institute.
In 1973, the Netherlands government gave $64,700 as part of a 5-year grant for the
institute's project for regional station development in Indonesia.
The names of other donors along with the areas supported and the amounts
received during 1973 are given below:
Imperial Chemical Industries, weed control, $5,000.
Potash Institute of North America and International Potash Institute, long-term
fertility experiments, $2,195.
Shell Chemical Co., applied variety-fertilizer trials, $5,358.
Stauffer Chemical Co., rice pest control, $3,000.
Bayer Philippines Inc., cooperative work with the Agricultural Productivity
Commission, $8,333.
NSDB, evaluation of promising rice selections and management practices in the
Philippines, $1,816.
NFAC, training of government extension technicians, $29,677.
During the year 1973, the construction of the phytotron by the Australian govern-
ment was almost completed with an estimated cost of $1,000,000.

Mr. Thomas R. Hargrove joined the institute as associate editor, office of information STAFF
services, in January. CHANGES
Dr. H. Shiga joined the soil microbiology department as visiting scientist in April,
to replace Dr. Tomio Yoshida, soil microbiologist, who departed in June for study
leave.
Dr. Amir U. Khan, agricultural engineer, went on study leave in June. Two months
later, Dr. Joseph K. Campbell joined as visiting associate agricultural engineer.
In July, Dr. Nyle C. Brady succeeded Dr. Ralph W. Cummings as director.
Dr. Randolph Barker, agricultural economist, went on study leave in July. Dr.
Robert Herdt joined as visiting agricultural economist in August.
Mr. Orlando Santos, associate farm superintendent, took study leave beginning
in August.

RESEARCH HIGHLIGHTS xxxvii

There were several changes in the institute staff in international programs.
Dr. Reed Bunker, Dr. Hiroshi Sakai, and Mr. Ernest Nunn resigned their positions
with the All-India Coordinated Rice Improvement Project.
Mr. Rufus Walker resigned as rice adviser, Bangladesh Rice Research Institute,
in June.
Dr. John M. Green joined the IRRI program in Indonesia in June as corn breeder
and seed certification specialist.
In December, Dr. Jerry L. McIntosh joined the IRRI-Indonesia-USAID Cooper-
ative Project in Indonesia as agronomist.

TRUSTEES Dr. Virgilio Barco of the International Bank for Reconstruction and Development,
U.S.A., was appointed to the Board. Dr. Tosi Take lida, director of the Institute for
Plant; Virus Research, Japan, replaced Dr. Noboru Yamada of the Ministry of
Agriculture and Forestry, Japan, who had completed his term of appointment. Dr.
N. C. Brady replaced Dr. R. W. Cummings, who resigned as institute director in
November last year.

xxxviii IRRI ANNUAL REPORT FOR 1973

Crop weather

During 1973, 2,206 mm of rain fell, compared
with the 7-year average of 1,981 mm. Most of the
rain fell in October, November, and December
while most of last year's rain fell in June, July,
and August. Twice as much rain fell during
October and December this year compared with
the same months last year. On November 21, 236
mm of rain fell in a single day, the largest
amount in 26 years. The rainfall was fairly
uniform starting in August which helped both
rainfed lowland and upland rice, which are
entirely dependent on rain for moisture supply.
There were more rainy days (0.25 mm and

Solar radiation ( kcal cm-2 wk- )
41 J e 1973

Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Solar radiation and rainfall (three-point moving weekly
average) at IRRI, 1973 and 1966-72. Shaded area shows the
standard deviation of the 7-year average.

Table 1. Number of rainy days (0.25 mm or more). IRRI,
1966-1972 (avg), 1972, and 1973.

Month Rainy days (no.)
Month
Avg 1966-72 1972 1973
January 13 14 9
February 6 4 6
March 7 7 7
April 5 9 6
May 16 18 9
June 20 18 16
July 24 31 19
August 20 21 24
September 22 22 23
October 18 15 22
November 19 24 21
December 18 11 23

greater) during August and December this year
than the averages for the previous 7 years (see
table). Long-duration rice varieties grown under
upland conditions at IRRI farm were helped by
late rain. One late-maturing experimental line
produced 4.7 t/ha under upland rice culture
while several produced over 4 t/ha.
The high solar radiation in May and June this
year benefited the ripening period environment
of the dry-season crop. Because of high rainfall
in September and October, solar radiation was
lower this year than last year. In December, there
was 4.0 kcal/sq cm less solar radiation than a
year earlier and 2.5 kcal/sq cm less than the
December average for the past 7 years. The low
sunlight in December was not harmful to most of
the wet-season crop, except the very late-matur-
ing crop.
Tropical depressions occurred on October 7,
October 24, and November 19 this year. The
tropical depression on October 7 caused severe
damage to many wet-season crops which were
maturing and to those close to harvest. Never-
theless, 1973 can be considered a year of few
typhoons.

CROP WEATHER xxxix

Nutritional studies in pre-
Che mis0try school children and with
Streptococcus zymogenes indicated that high protein rice has better
nutritional value than rice with average protein. In studies of indicators
of grain protein content, nitrogen content and nitrate reductase ac-
tivity of seedlings were not reliable. Plant selections from two higher
lysine varieties were no higher in lysine content than the parents. El A
rapid, simple test, complementary to the amylose test, was developed
based on consistency of a cold 4.4 percent milled-rice paste in 0.20 N
KOH. Gel consistency values correlate with amylograph setback
viscosity and measure the relative rate of retrogradation of the starch
gel. Differences in gel consistency were found in samples of similar
amylose content especially above 24 percent amylose. In a study of
mutants differing in grain shape from the parent, amylose content and
amylograph viscosity of the grains were similar to those of the parent.
O Parboiling caused a loss of thiamine and a diffusion of thiamine to
the endosperm both of which depended on the severity of heat treat-
ment. E Waxy rice suitable for Philippine flattened parboiled rice and
rice cake had low gelatinization temperature and lower gel consistency
than poor quality waxy rices. Rice suitable for fermented nonwaxy rice
cake had 24 to 26 percent amylose for adequate gas retention during
fermentation and steaming, and for soft texture of the cake. E Neutral
oils extracted from bran-polish and milled rice with petroleum ether
had similar fatty acid composition. Polar oils extracted with methanol/
chloroform had higher linoleic acid content than neutral oils. O Starch
synthetase bound to the starch granule was solubilized with retention
of activity by dispersion of amorphous starch in 75 percent dimethyl-
sulfoxide with ultrasonic waves.

GRAIN PROTEIN

More than 21,000 rice samples from breeding
and genetic studies were analyzed for Kjeldahl
protein in 1973 as part of a cooperative program
to raise the protein content of rice by 2 percen-
tage points.
Protein quality. The microbiological quality
of milled rice samples differing in protein con-
tent was assayed by O. Mickelsen and D.
Makdani (Michigan State University, U.S.A.).
The growth rate of Streptococcus zymogenes
was used as indicator of protein quality with
casein as the standard (100 %). They found that
microbiological quality corresponded well with
chemical score based on lysine except for the
high value for IR480-5-9 milled rice (Table 1).
The correlation coefficient with microbiological
qualitywas0.86** for chemical score and -0.75*
for protein content. The drop in microbiological
value was only about 10 percent for an increase
in protein content of over 100 percent.
Nitrogen balance studies in pre-school chil-
dren were started with C. L. Intengan, Food and
Nutrition Research Center, Manila. In earlier
trials in which IR480-5-9 milled rice with 11.9
percent protein (N x 6.25) was used as the sole
source of protein (mean intake of 314 mg N/kg
body weight daily) for four children, nitrogen
absorption was 75 percent of nitrogen intake and
nitrogen retention was 37 percent of intake. But
difficulty was encountered because some chil-
dren needed more than three feedings a day to
reach the required intake of nitrogen.

Table 1. Biological value of milled rices differing in
protein content and chemical score of protein based on
relative growth of Streptococcuszymogenes (0. Mickelsen
and D. Makdani, Michigan State Univ., U.S.A.).
Micro-
Protein Lysine Chemical bioicra
Sample biological
(% N x 6.25) (g/16 g N) score (%) valueb()

Intan 5.97 4.07 74 71.8
IR8 7.69 3.59 65 68.7
IR22 7.88 3.75 68 69.4
IR22 10.0 3.87 70 70.0
IR8 10.2 3.50 64 65.9
IR1103-15-8 11.6 3.65 66 70.0
IR480-5-9 11.8 3.34 61 68.4
BPI-76-1 15.2 3.19 58 63.4
aBased on 5.5 g lysine/16 g N (1973 pattern) as 100%. bBased
on 100% for casein.

In this year's trials three milled rice samples
with 7.7, 10.3, and 11.9 percent protein were
used in a diet which had a constant rice-to-fish
ratio of 100:17. The fish fillet (surgeon, Acan-
thurus bleakeri) had 20 percent protein and 10
percent lysine in its protein. Rice was fed at the
daily rate of 10 g/kg body weight. Each diet was
fed to each child for an adaptation period of 4
days, then for 6 days feces and urine were
collected. Composite diets were also analyzed
for amino acid composition. Each child was fed
the low protein rice, and then either the high
protein or the intermediate protein rice. Results
so far indicate that diets with higher rice protein
content had a lower chemical score (Table 2).
Percentage nitrogen absorption and retention,
however, were maintained so that higher protein
content of rice gave a higher value for nitrogen
balance. Nitrogen intake was probably inade-
quate in the lower protein rice diets and part of
the protein was probably used for energy. The
IR8 diet gave the widest range of nitrogen
balance values.
High-lysine rice. We previously found that in
two successive crops, the varieties ARC 10525
and Kolamba 540 had 0.5 percentage point
higher lysine content of protein than IR8. In the
1973 dry season, brown rice from the best three
single plant selections identified in 1972 from
these varieties were screened for Kjeldahl protein
and dye-binding capacity (lysine) and the best
samples were analyzed for lysine by column
chromatography. We found that the best sam-
ples still had lysine contents only 0.5 percentage
point higher than that of IR8 and they were no
higher than that of pooled sample. Because of
the limited reproducibility of existing screening
methods and the inherent variability in lysine
content within a variety, attempts to breed high
lysine varieties cannot be justified unless an
increase of 1 percentage point is possible.
Milled rice protein of these two varieties also
had higher lysine content than that of IR8 rice
(Table 3). Extraction of milled rice protein with
5 percent sodium chloride solution and sub-
sequent protein and lysine analysis of the
fractions revealed that the cause of the higher
lysine content of ARC 10525 protein was its
higher level of salt-soluble protein (specifically
globulin). Kolamba 540 tended to have a higher

2 IRRI ANNUAL REPORT FOR 1973

Table 2.Mean chemical score and mean nitrogen balance of rice/fish diets (100:17 wt/wt) fed to pre-school children
(C. L. Intengan. Food Nutr. Res. Center, Philippines).
Daily Daily
Rice Chemical nitrogen Nitrogen Nitrogen nitrogen
Milled rice protein Children' score of intake absorbedc retainedc balance
source (% N x 6.25) (no.) dietb (%) (mg/kg) (%) (%) (mg/kg)
IR8 7.7 7 99 191 72 29 55
IR480-5-9 10.3 6 91 236 74 32 74
IR480-5-9 11.9 7 84 253 76 32 82
LSDd (5%) 5 17 n.s. n.s. 21

"Five children partook of three diets. bBased on 5.5 g lysine in 1973 provisional amino acid pattern. cCompared with intake. dBased
on the five children who partook of the three diets.

lysine content of salt-soluble and salt-insoluble
(residual) protein than IR8. Disc electrophoresis
showed no varietal differences in the protein
bands of the soluble protein fractions of the
three varieties.

GRAIN QUALITY
Gel consistency. A rapid, simple test, which is
complementary to the test for amylose content,
was developed based on the consistency of a cold
4.4 percent (dry basis) milled-rice paste in 0.20
N KOH. This test can be used to distinguish
differences in the texture of cooked rice of
nonwaxy varieties that have the same amylose
content. To conduct the test, rice powder (100
mg at 12 % moisture) is placed into 13 x 100 mm
culture tubes and wetted with 0.2 ml 95 percent
ethanol containing 0.025 percent thymol blue.
The tube is shaken to suspend the starch, then
2 ml of 0.2 N KOH is added and the mixture is
dispersed using a Vortex Genie cyclone mixer
(setting of 6). The tubes are covered with glass
marbles and placed for 8 minutes in a vigorously
boiling water bath to reflux. The samples are
removed from the water bath, set at room tem-

perature for 5 minutes, and then cooled in an
ice-water bath for 15 minutes. Consistency is
measured by the length in a test tube of the cold
gel held horizontally for 30 minutes or 1 hour
over ruled paper graduated in millimeters (fig. 1).
The coefficient of variability was 4 percent of the
mean of duplicate runs. One hundred samples a
day can readily be run in duplicate by one
technician.
The consistency values are correlated with
amylograph setback viscosity (fig. 2) and can
differentiate three consistency types-high (26
to 35 mm), medium (36 to 50 mm), and low (51
to 100 mm). The test is especially useful for
differentiating samples that have 24 to 30 percent
amylose. For example, of 38 lines having 24 to
30 percent amylose with BPI-121-407 as parent
(24 to 26% amylose and low gel consistency),
nine had high consistency, 12 had medium
consistency, and 17 had low consistency. Aging
of raw rice has little effect on gel consistency.
And, samples of the same variety differing in
protein content by as much as 5 percentage
points gave similar gel consistency values.
Consistent atypical gel consistency values
were obtained in one out of four to six samples

Table 3. Lysine content of total protein and of two protein fractions of milled rice of two higher lysine rice varieties as
compared with IR8.

Total protein Albumin-globulin
Variety Lysine content*
Of milled rice Lysine content' Of total protein Lysine content' of residual protein
(%) (g/16.8 g N) (%) (g/16.8 g N) (g/16.8 g N)
ARC 10525 9.6 3.92 13.9 4.40 3.78
Kolamba 540 8.2 4.06 11.8 4.72 3.86
IR8 (check) 7.0 3.63 10.7 4.51 3.45
'LSD (5%): 0.37 g/16.8 g N.

CHEMISTRY 3

1. Typical 4.4 o pastes of rice with high, medium, and low gel consistency.

of the same variety in three of the varieties tested.
Samples of the same variety also differed widely
in amylograph setback viscosity.
Resurvey of world rice. In the early 1960's we
obtained rice samples from rice producing
countries to check the amylose content of
varieties. This year we resurveyed the amylose
content of world rice after the introduction of
the semidwarf rice varieties using the more
accurate simplified assay for amylose developed
in 1971. Amylose content can be classified as
low (< 20 %), intermediate (20 to 25 %), moder-
ately high (25 to 27 %), and high (27 to 33 %). Gel
consistency values were also determined on these
samples.
The amylose contents of the indica and
japonica rices overlapped (Table 4). The highest
amylose content for a japonica variety was 27
percent for Ponta Rubra from Portugal. Most
japonica varieties, except those from Egypt,
France, and Italy, gave low gel consistency
ratings. Hence, amylose content differentiates
varieties better than gel consistency for rices
from Japan, South Korea, Bulgaria, Portugal,

U.S.S.R., and U.S.A. Egyptian rice with poor
eating quality (25% amylose) had high gel
consistency. The French variety Arlesienne
(24% amylose) also had high gel consistency.
The Italian variety Raffaello (25 % amylose) had
medium gel consistency.
Among tropical rice varieties, low amylose
rices of good eating quality such as Khao Dawk
Mali 105 from Thailand and Chhuthana from
Khmer had low gel consistency. Among tropical
rices with an amylose content above 24 percent,
most had a low gel consistency, even those with
above 27 percent amylose. Four out of five
market samples of fine-grain rice in Hongkong
(28 to 30 % amylose) had low g6l consistency and
the fifth sample had high consistency. The new
Indian variety IET 1991 and the premium South
Vietnamese variety Tau Huong had low gel
consistency. Both had high amylose content.
Among the IRRI varieties, the gel consistency
of IR5 and IR24 was low; of IR26, low to
medium; of IR20, medium; and of IR8 and
IR22, high. The amylose content of IR24 was
low; of IR20 and probably IR26, moderately

4 IRRI ANNUAL REPORT FOR 1973

- _------e

high; and of IR5, IR8, and IR22, high. The
dwarf varieties from Taiwan, which were the
source of the dwarfing gene in IRRI varieties,
all had high amylose and high gel consistency.
Among 16 Philippine rices with 26 to 32
percent amylose, consumer panels conducted by
home technologists at University of the Philip-
pines at Los Bafios gave highest scores for
cooked rices with low gel consistency, followed
by those with medium consistency, and then
those with high consistency. The check variety
C4-63G (25 % amylose) with a high preference
score also had low gel consistency. The upland
varieties Azucena, C22-51, Dinalaga, Man-
garez, and Palawan were verified to have
intermediate amylose content (23 to 25 %). The
prized aromatic variety Milagrosa had 24 per-
cent amylose and had low gel consistency.
The results indicate the applicability of gel
consistency in differentiating varieties of similar
amylose contents above 24 percent amylose. In
general, low gel consistency is preferred over
medium or high consistency among these rices.
A notable exception is Basmati-type rice which
may give medium gel consistency.
Final gelatinization temperature was mainly
low (<70"C) forjaponica rice and either low or

Amylogrph setback viscosity ( Brobender units )
800

600

400
*
*
200

0 C

-200 -
0
-400 *0

30 40 50 60 70 80 90 100
I-high-----mediumt --- low --
Length of gel (mm )
2. Relation of gel consistency (length of 4.4 % milled-rice gel
in 0.20 N KOH) to amylograph setback viscosity of 9%
paste.

intermediate (70 to 74"C) for indica rice (Table
4). High gelatinization temperature (>74C)
was restricted to waxy and low amylose rices.
Mutants differing in grain shape. Workers in
India have produced mutants of indica and
japonica rices differing in grain shape which they
reported to also vary markedly in quality and

Table 4. Ranges of amylose content, and gel consistency and gelatinization temperature types of milled rice obtained
from rice-producing countries.

Varieties tested Amylose content range Gel consistency Gelatinization
(no.) (% dry basis) typesa temperature types*
Asia
Bangladesh 20 20-29 L > M > H I > L
India (Hyderabad) 18 20-29 L > H > M L > I
India (Maharashtra) 14 23-28 M > L > H I > L
Japan 12 18-21 L L
South Korea 10 21-24 L L
Khmer 9 18-28 H > L I > L
Nepal 16 23-27 L > M, H L > I
Philippines 18 23-31 L > M, H L > I
Thailand 12 16-28 L, M, H L > I
South Vietnam 17 23-30 L I
Outside Asia
Bulgaria 5 19-22 L L
Egypt 9 19-25 L > H L
France 8 20-24 L > H L
Italy 10 19-25 L > M L
Portugal 10 21-27 L L
U.S.S.R. 7 19-22 L L > H
U.S.A. short & medium 8 18-20 L L
long 6 26-27 L I

*L = low; M = medium; I = intermediate; H = high.

CHEMISTRY 5

amylose content from the parent. These mutants
were termed "indica" or "japonica" depending
on the shape of their grain. Because of the poor
correlation between amylose content and grain
shape, we analyzed a crop of mutants of Tainan
3, TNI (Taichung Native 1), and IR8 grown at
IRRI. The three "indica" mutants of Tainan 3
had 12 to 17 percent amylose while Tainan 3
itself had 19 percent. The three "japonica"
mutants of TN1 had 28 to 29 percent amylose
while TN1 itself had 28 percent. Similarly IR8
had 29 percent amylose and its four fine-grain
mutants had 28 to 30 percent amylose. The
amylograph set-back viscosity of these mutants
were similar to that of the parent sample. Hence,
the amylose contents of the mutants were similar
to those of the parent varieties, in spite of the
change in grain shape so it is misleading to call
them indica or japonica mutants.
Parboiling and nutrients of grain. Previous
studies (1968) showed that parboiling causes
little or no redistribution of protein in the rice
grain. This year we studied whether water-
soluble vitamins such as thiamine (vitamin B,)
diffuse into the endosperm during parboiling.
Aside from laboratory samples, parboiled rice
samples from U.S.A. and Sri Lanka were ana-
lyzed. We found that parboiling decreased the
thiamine content of brown rice due to heat
degradation (Table 5). The least degradation
was shown by samples from hot-sand parboiling
(a method developed by IRRI agricultural
engineers) with a heating time of less than 0.5
minute. Parboiling for 10 minutes at 121"C
caused greater loss of thiamine than parboiling
for 20 minutes at 100C.
Milled parboiled rice, however, contained
more thiamine than milled raw rice at the same

degree of milling (Table 5) because parboiling
caused thiamine to diffuse inwardly. Both the
degree of loss and the degree of diffusion de-
pended on the severity of heat treatment. This
inward diffusion was verified by thiamine assay
of three successive outer milling fractions and of
the residual grain of raw and parboiled IR22 rice.
The bran-polish of parboiled rice had a higher
fat and protein content than bran-polish of raw
rice at the same degree of milling (Table 5). The
starchy endosperm of parboiled rice has a great-
er resistance to milling, hence the bran-polish
and the germ were more completely removed.
Milled parboiled rice, however, was not sig-
nificantly lower in protein content than milled
raw rice. The starch content of bran-polish from
parboiled rice was lower than that of bran-polish
from raw rice.
We verified that the degree of parboiling and
percentage of parboiled grains are measured by a
modified alkali test developed by Indian work-
ers. Soaking milled rice for 1 hour in 1 percent
KOH caused some disintegration in parboiled
rice and no swelling in raw rice even for IR22
which has a low gelatinization temperature.
Flattened parboiled waxy rice. Five waxy rices
from the 1972 wet season crop were studied for
physicochemical properties and suitability for
making pinipig (a Philippine flattened parboiled
waxy rice). Storage of the pinipig for a few weeks
amplified sample differences in stickiness of
pinipig after hydration. The final gelatinization
temperature of starch granules of Philippine
waxy lines was either low (<70C) or high
(74.5"-79'C). Pinipig processors preferred Ma-
lagkit Sungsong because as hydrated pinipig it is
more tacky or sticky than pinipig from other
waxy rices even after storage (Table 6). Com-

Table 5. Effect of parboiling method on nutrient content and distribution in brown rice (at 14% moisture).

Treatment Degree of Thiamine (pg/g) Protein (%) Bran-polish
milling (%) Brown rice Milled rice Milled rice Bran-polishfat ()
Laboratory method (hot soak) (IR20 and IR22)
Raw (check) 11.6 3.80 0.58 9.0 13.4 16.6
Treated 100 C 11.1 3.60 0.95 8.7 13.6 17.4
Treated 121 C 12.0 3.17 2.94 8.6 15.0 19.8
Heated-sand drying (IR20 and IRRI line)
Raw (check) 10.5 3.72 0.56 8.2 13.6 16.8
Treated 10.2 3.61 1.80 7.8 13.8 18.4
LSD (5%) 0.8 0.39 0.55 0.9 0.5 2.7

6 IRRI ANNUAL REPORT FOR 1973

pared with the four other rices it had higher
alkali spreading values corresponding to a lower
gelatinization temperature of starch granules.
The amylopectins differed in molecular size, as
indexed by sedimentation constant, and in mean
chain length. Using a 9-percent neutral rice gel
we found that increasing stiffness of the gel
corresponded to a decrease in stickiness of
hydrated pinipig. Malagkit Sungsong also had a
higher level of hot-water soluble starch than the
other samples.
Thus waxy rice suitable forpinipig-making has
a low gelatinization temperature and a low gel
consistency (of 9 % paste). The relatively low
molecular weight of amylopectin in the samples
with low gelatinization temperature probably
contributes to the stickier texture and softness of
hydrated pinipig.
Waxy rice cake. Thirteen waxy lines from
1973 dry-season yield trials of the University of
the Philippines at Los Bailos were assessed for
suitability for suman (a Philippine waxy rice
cake) by home technologists at UPLB. Three
parts milled rice were cooked with five parts
coconut milk, then wrapped in banana leaves

and steamed. A consumer panel gave higher
scores to samples that had low gelatinization
temperature than to those that had high gelati-
nization temperature, but the scores for the
two types overlapped (Table 7). Measuring
stickiness using a beam balance technique gave
similar results. In previous tests freshly boiled
waxy rice gave similar taste panel scores regard-
less of gelatinization temperature. But the soft-
ness of suman which had been stored at 4*C for
several days clearly differentiated samples that
had high gelatinization temperature from those
with low gelatinization temperature, with the
exception of IR833-6-2. Softness was determined
by an improvised penetrometer. Waxy rice with
low gelatinization temperature is preferred for
the preparation of waxy rice cake because it has
a slower rate of retrogradation or hardening of
cooked rice as compared with rices with high
gelatinization temperature. Values for hot-
water-soluble starch (11.3 to 13.4% glucose)
overlapped among the two gelatinization-tem-
perature classes.
The behavior of the IR833-6-2 sample was
anomalous because it was one of the better lines

Table 6. Physicochemical properties of waxy rices differing in the quality of hydrated stored pinipig.
Milled rice Starch
Stickiness of Alkali Gel Final Sedimentation
Variety or line hydrated pinipig spreading consistencyb gel. constantc, S o.w
(g/g hydrated pinipig) value' (mm) temp. (*C) (S)
Malagkit Sungsong 336 6.0 68 61 82
IR833-6-2 192 5.0 54 65 66
IR833-34-1 125 5.0 56 67 58
IR253-16-1 120 5.0 45 70 58
Panpet 63 32 2.3 28 77 242
LSD (5%) 40 0.3 6 3 20

ORange: 1 = low, 7 = high. bModified procedure using 200 mg rice powder (12% moisture) gelatinized with 1 ml 0.3 N KOH; gel is
neutralized with 1 ml 0.3 N acetic acid. cO.5% solution in dimethylsulfoxide.

Table. 7. Properties of waxy lines differing in starch gelatinization temperature and in softness of cold rice cake.
Milled rice Rice cake
Lines Final Alkali Gel Preference Stickiness Softness
gel. temp. spreading value consistencya (mm) score (g/cm2) index (mm)
Four lines high 2.7 0.20 37 + 2.9 -2.1 + 0.19 7.3 + 0.16 0.6 0.23
Seven lines low 6.4 + 0.17 64 + 4.9 1.6 + 0.24 5.7 + 0.23 11.5 + 0.47
IR833-6-2 low 6.4 60 -3.4 7.1 0.7
IR253-4 (check) low 6.1 64 2.1 5.6 13.6
LSDc (5%) 0.3 9 0.6 0.3 0.7
a200 mg rice in 2 ml 0.1 5N potassium acetate. bTotal of 12 assessments persample. 39 judges given four sampleseach with scores between
1.03 to -1.03 (Mrs. A. M. del Mundo, home technology dept.. University of the Philippines at Los Banos). cSample mean.

CHEMISTRY 7

Peak viscosity ( Brabender units )
12001

Months of storage
3. Effect of storage on amylograph peak viscosity of 9'%
starch paste of four rices differing in amylose content.
IR833-6-2 milled rice is waxy, IR24 has 18% amylose,
IR480-5-9 has 24% amylose, and IR22 has 29'/, amylose.

for pinipig preparation. But the low preference
scores coincided with its poor stickiness index.
With IR833-6-2 excluded (n = 12), the cor-
relation coefficient with softness was 0.92** for
alkali spreading and 0.92** for gel consistency.
The corresponding values with IR833-6-2 in-
cluded (n = 13) were 0.78** and 0.83**.
Fermented nonwaxy rice cake. Rice varieties
suitable for making fermented nonwaxy rice
cake (puto) produce dough which retains gas
adequately during yeast fermentation and give
steamed cake with good texture. C4-63G is the
variety manufacturers prefer. Among 10 rices
aged for a year prior to milling, gas retention
during fermentation of the dough tended to
decrease with increasing amylose content and
was higher for waxy rice. In addition, relative
viscosity of the dough using a pipette also was
negatively correlated with amylose content,
indicating cohesion between raw starch granules.
Since rice dough, unlike wheat, has no gluten, gas
retention during fermentation is probably due to
cohesion of starch granules in the dough as
affected by amylose content. The effect of

protein content on these properties was not
clear-cut.
During steaming, however, waxy and low
amylose rices were not able to retain the en-
trapped gas (CO2) while rice with 24 to 26
percent amylose (C4-63G, Intan, BPI-76-1)
showed adequate gas retention resulting in good
volume expansion. Intermediate amylose con-
tent also insured a soft texture for the steamed
cake. These rices also had low gel consistency,
except for IR20 which had medium gel consist-
ency.
Mechanism of rice aging. Most studies on the
changes rice undergoes during storage have been
made with milled rice although rough rice and
brown rice are known to undergo the same
changes during storage. To obtain a general
mechanism of rice aging, rough rice, milled rice,
surface-defatted milled rice, and rice starch of
four samples with 0, 19, 24, or 29 percent
amylose from the 1972 dry season crop were
stored at 4C and 28C for 6 months. Samples
differing in protein content were also included.
In general, all samples showed similar changes
regardless of the form of storage, amylose
content, or protein content. Most notable was
the increase in amylograph peak viscosity re-
gardless of amylose and protein contents (fig. 3
and 4). Denaturation of the a-amylase of brown
rice flour by acidification and subsequent neu-
tralization did not result in an increase in
amylograph peak viscosity of freshly harvested
rice. Volume expansion and water uptake during
cooking increased while dissolved solids de-
creased progressively, particularly in samples
stored at 28C. Hardness values (as indexed by
percentage of powder coarser than 80 mesh after
grinding 20 seconds in a Wig-L-Bug amalga-
mator) increased with aging. They were higher
for the high protein sample of each rice. Free
fatty acids were highest in milled rice stored at
28"C compared with defatted milled rice at 28C
and control samples at 4C. No trend was found
for in vitro digestibility of cooked rice with r-
amylase, amylose, and protein content, and in
the gelatinization temperature of starch. Sticki-
ness measured by the beam balance technique
showed no change in value for cooked waxy rice
but showed significant decreases for the 19 and
24 percent amylose samples. The technique was

8 IRRI ANNUAL REPORT FOR 1973

Peak viscosity ( Brabender units)
900

0 5 10 15 20 25 30
Amylose content (% dry basis )
4. Effect of storage (for 6 months at 28*C + 3"C) on the
amylograph peak viscosity of low and high protein milled
rice of three varieties.

not sensitive enough for flaky rice (29%
amylose).
All the major fractions underwent changes
during aging. The solubility of starch in hot
water decreased. Since high protein samples and
surface-defatted samples behaved similarly to
milled rice, and since starch also showed similar
amylograph changes to those in milled rice, the
starch fraction probably contributed more to
the changes during aging than protein and fat.
Composition of rice oils. Ten years ago we
found that oil from milled rice has lower iodine
value (is more saturated) and smaller amounts

of essential fatty acids (mainly linoleic) than
bran-polish oil. Since later studies elsewhere
showed the opposite relationship using chloro-
form/methanol (2/1 vol/vol) instead of petro-
leum ether, we restudied, by gas chromato-
graphy, the fatty acid composition of oil extrac-
ted from bran-polish and milled rice of IR20 and
IR22. Methyl esters were prepared by refluxing
oil in methanolic HC1.
The fatty acid composition of oils extracted
from bran-polish and milled rice with petroleum
ether were similar and the ratios of oleic acid to
linoleic acid were about 1.0 (Table 8). Milled
rice oil extracted with methanol/chloroform,
however, contained more linoleic acid and less
oleic acid than oil extracted with petroleum ether.
Thus, oil extracted by the polar solvent meth-
anol/chloroform was more unsaturated than
neutral oils extracted with petroleum ether.

SEED AND PLANT METABOLISM
Oxygen uptake, peroxidase, and grain dormancy.
Studies last year indicated rice hulls have a high
peroxidase activity and that dehulling increases
germination of dormant grain. But oxygen
uptake, measured by Warburg manometry, did
not show a corresponding increase after de-
hulling. Changes in oxygen uptake, peroxidase
activity, and dormancy were examined during
the development of the grain (variety H4) in the
1973 wet season. Ripening grains were assayed
with and without air-drying. We measured
oxygen uptake by a polarographic assay with
the Clark oxygen electrode on grains which had
been soaked for 2 hours. Oxygen uptake of the

Table 8. Fatty acid composition of oils from bran-polish and milled rice of IR20 and IR22 extracted with petroleum
ether or methanol/chloroform.
Compositions (%)

Fatty acid Bran-polish oil Milled rice oil
pet. ether pet. ether methanol/chloroform LSD
IR20 IR22 IR20 IR22 IR20 IR22 (5%)
Palmitic 0.4 0.3 0.7 0.3 1.4 0.9 0.2
Myristic 19.8 18.4 23.0 17.9 23.1 22.6 3.2
Stearic 1.6 1.4 1.7 2.1 1.4 1.6 n.s.
Oleic 38.5 40.7 37.8 38.1 27.0 28.5 2.3
Linoleic 37.4 36.5 34.6 38.3 46.1 45.2 2.1
Linolenic 2.3 2.7 2.2 3.3 1.0 1.2 n.s.

'Percent by weight. Trace palmitoleic acid present in bran-polish and milled rice oils; trace lauric acid found in milled rice oil only.

CHEMISTRY 9 .

whole grain decreased progressively during
ripening. The dehulled fresh grain (brown rice)
had 4 to 29 times higher rates of oxygen uptake
than the whole grain and dehulled air-dried
grain had four to six times higher rates partic-
ularly during the first 2 weeks of grain develop-
ment. Peak uptake for dehulled grain occurred
about 10 days after flowering (623 nmol/h 02).
Germination of dehulled air-dried developing
grain was nil in the 4-day grain (i.e., 4 days after
flowering), 45 percent in the 7-day grain, 67
percent in the 10-day grain, and 87 percent in
the ripe grain. Fresh grain failed to germinate.
Peroxidase activity was constant during the
first 3 weeks of grain development (1.2 to 1.4
nmol purpurogallin min- seed- ') but de-
creased during grain desiccation (to 0.22 nmol
purpurogallin). The hull contributed from 80 to
90 percent of peroxidase activity of rough rice.
The results are consistent with the reported
viability and complete formation of the embryo
1 week after flowering.
A comparison of dormancy and 02 uptake of
ripe H4 seeds showed that the oxygen uptake of
fresh rough rice (0 % germination) was 8 nmol/h,
that of air-dried rough rice (1.3% germination)
was 12 nmol/h, that of fresh brown rice plus hull
(78 % germination) was 34 nmol/h, and that of
air-dried dehulled rice plus hull (87% germin-
ation) was 53 nmol/h. Apparently the hulls of
dormant grain are a barrier to oxygen uptake by
the rice seed thus retarding germination. Oxygen
uptake by nondormant rough or brown rice
increased progressively during the first 6 hours
of soaking.
Pricking brown rice at the distal end before
soaking in water for 20 hours did not increase
oxygen uptake (42 nmol/h), but pricking at the
embryo end increased oxygen uptake to 56
nmol/h. No difference occurred in seeds soaked
for 2 hours. Since pricking brown rice near the
embryo results in complete germination, the
aleurone layer and seedcoat, as well as the hull,
reduce the oxygen uptake of the embryo. Thus
the apparent dormancy of the rice grain is not
seed dormancy, rather the covering structure of
the nondormant embryo restricts oxygen dif-
fusion, thus preventing germination.
Dry matter loss during grain soaking. Indian
workers have reported that grains of the semi-

dwarf varieties are less suitable for parboiling
than grains of traditional rice varieties due to
greater dry matter loss during soaking. In
addition, the breakdown products act as sub-
strate for microbial growth in the steeping
water. Since the new varieties have weaker
dormancy and different starch properties (par-
ticularly gelatinization temperature) than the
traditional varieties, we studied the rate of
release of free sugars and dry matter loss of
varieties differing in gelatinization temperature,
presence of white belly, and amylose content at
different degrees ofdormancyduring soaking for
1 to 4 days in water at 30C.
Dormancy and endosperm opacity contrib-
uted to differences in dry matter loss. Dormant
samples released sugar in the soaking water
more slowly. In addition because another
contributing factor was their characteristic
white belly, IR8 and IR5 rice gave higher free
sugar formation after 1 day of soaking than a
waxy rice sample. Presumably, the air spaces
between starch granules in the white-belly
portion of IR8 and IR5 allow faster dry matter
loss than the air spaces in the starch granules of
waxy rice. Nondormant IR22 grains with trans-
lucent endosperm and low gelatinization tem-
perature had similar rates of dry matter loss to
nondormant H4 with intermediate gelatinization
temperature. That indicates that gelatinization
temperature of starch is a minor factor in dry
matter loss during soaking.
Enzyme changes during germination. We
studied the endosperm enzymes, catalase and
cellulase, for changes in germinating IR8 grain.
Catalase levels increased progressively during
germination in light and reached a maximum
(15 times that of the mature grain) on the sixth
day of germination. The changes followed a
trend similar to those of peroxidase. Cellulase
activity, measured by release of reducing sugars
from carboxymethyl cellulose, showed a first
peak on the third day of germination followed
by a decrease during the fourth to the sixth day
and an increase again in activity on the seventh
day.
The sequence of production of phytase, lipase,
and fl-1,3-glucanase was studied in embryo-less
IR8 seed halves incubated in 0.2 pM gibberellin
A3. In germinating IR8 grains, they are pro-

10 IRRI ANNUAL REPORT FOR 1973

duced in the endosperm in the order: phytase,
lipase, fl-glucanase. In the embryo-less seed
halves, phytase was produced first, followed by
fl-glucanase and lipase together. Lipase produc-
tion was delayed and its activity was slower in
this artificial medium. Phytase activity was lower
but that of fl-glucanase was higher. Delayed
lipase production has been also reported in
wheat seed halves. Glutamine and hydroxyla-
mine(1 mM) which accelerated lipase production
in wheat had no effect on rice lipase production.
Production of fl-glucanase coincided with pro-
duction of a-amylase in the embryo-less seed
halves in gibberellin A3. Thus hydrolases in the
rice aleurone layer were produced in sequence
during germination and during incubation in
gibberellin A3.
RNase (ribonuclease) is a key enzyme of
nucleic acid metabolism in developing and
germinating grain. RNase I or cytoplasmic
RNase is found in large amounts in developing
and mature corn. In a study on RNase I in
degermed IR480-5-9 grain, the highest activity
was in a sample germinated 4 days in the dark
(46 AA260 30 min-'1 grain-'), followed by
developing grain at midmilky stage (17 AA260
30 min-' grain-1) and least in the mature
grain (3AA 260 30 min-' grain '). Disc
electrophoresis indicated the presence of one
major fast-migrating, distinct, and very active
RNase isozyme band in the endosperm of
developing and germinating grain. The RNase
isozyme was not distinct in the mature grain
although a corresponding protein band was
present in the extract. The major RNase band
was identical in both germinating and develop-
ing grain: the band had the same width in a
mixture of the two extracts. Two minor, slower
migrating RNase bands were present in the
developing grain but absent in the other samples.
Lipase production in bran. The foregoing
results on rice seed halves incubated in gibber-
ellin A3 indicated a delayed production of lipase
compared with the germinating seed. Since fat
hydrolysis by lipase is the major reason for the
poor keeping quality of rice bran, the nature of
lipase production in rice bran was examined.
Preliminary studies indicated that the aleurone
layer produced free fatty acids at least three
times faster than the germ fraction. The cells of

the aleurone layer were probably more damaged
during milling than those of the germ.
Starch synthetase of grain. Starch synthetase
is the key enzyme involved in converting
nucleotide glucose derivatives into amylose. It
is present mainly in a form bound to the starch
granule in nonwaxy rice, but a soluble fraction is
also found in developing rice grains. Previous
attempts to make the bound synthetase soluble
had limited success.
In cooperation with Dr. E. J. del Rosario of
University of the Philippines at Los Bafios
chemistry department, we isolated starch gran-
ules from developing IR8 grains at the midmilky
stage and purified them by repeated washing
with water, and then with 0.1 M phosphate
buffer (pH 7.2) containing 0.006 M magnesium
chloride. The washed starch had 2.0 percent
protein. The granules were made amorphous by
placing 200-mg lots in a Wig-L-Bug amalga-
mator for 30 seconds.The granules were dispersed
using ultrasonic vibration at 20 kHz for 1 hour
in 0.05 M HEPES (pH 7.5) containing 75 percent
dimethylsulfoxide and 0.001 M dithiothreitol,
and then centrifuged. About half of the residual
protein of the starch granules was dispersed by
this treatment and it had a specific activity for
starch synthetase essentially the same as that of
the washed granules. In the precipitate collected
by trichloroacetic acid addition to the protein
extract, the ratio of carbohydrate to protein
was 5.5.
In a discontinuous sucrose-density-gradient
centrifugation of the solubilized enzyme, two
opaque bands were present between 35 and 45
percent sucrose and between 45 and 55 percent
sucrose. The lighter band corresponded to peaks
in protein content and starch synthetase activity
in the absence of added glycogen primer. This
band was also the fraction with highest amylose-
iodine blue color. The heavier protein band had
no synthetase activity even in the presence of
primer. The results indicate that the lighter
enzyme fraction is tightly completed with
amylose which functions as primer for the
synthetase assay.
Disc electrophoresis of the solubilized enzyme
had three bands which stained for both protein
and carbohydrate. Two other faint bands were
obtained. The band of slowest mobility showed

CHEMISTRY 11

the most intense staining.
Seedling test for grain protein content. In
studies elsewhere on corn and wheat, the highest
activity of nitrate reductase occurred in 1-week-
old seedlings and correlated with grain protein
content. Since our previous studies with 2.5-
week-old seedlings showed no relationship
between grain protein and seedling protein
levels, we studied this relationship in younger
seedlings grown in Hoagland's solution contain-
ing 40 ppm of either ammonium or nitrate nitro-
gen. Low and high protein seeds of IR8 and
IR480-5-9 were used. We found greater differ-
ences and higher nitrogen levels in 1-week-old
seedlings than in 2-week-old ones. The total
protein of the active leaf (topmost fully expanded
leaf) was higher in IR480-5-9 than in IR8 due to a
heavier leaf and a somewhat higher protein level.
The difference in protein level and weight of total
tops was not significant. The high protein
samples of the two rices tended to have lower dry
matter production. Better foliage growth occur-
red in the ammonium medium than in nitrate,
and leaf protein levels were higher. Levels of
leaf nitrate reductase and root glutamate dehy-
drogenase were not related to grain protein
content.
Repetition of the screening using 21 promising
high protein lines did not reveal a trend between
foliar nitrogen and grain nitrogen. Hence
seedling vigor was not simply related to grain
protein content and the trend found for IR8 and
IR480-5-9 was due mainly to lower weight of the
active leaf and tops of IR8.
We also found that 1-propanol (5%) gave
higher values than two commercial surfactants
as wetting agent in the in vivo assay for nitrate
reductase in segments of rice leaf blades.
Effect of herbicides on seedlings. Two weeks
after flooded soil in which 2.5-week-old IR22
seedlings were growing was treated with 0.075-
ppm simetryne or 0.15 ppm benzomarc, the
leaves of the plants had higher total dry matter
but the same nitrogen level as leaves of the un-
treated control. In addition, levels of chlorophyll
and free amino acids were higher in leaves of the
treated plants. The glutamate dehydrogenase
activity was lower in roots of treated plants due
to the lower level of soluble protein since specific

glutamate dehydrogenase activity was at least
as high as in control plants.
Leaf proteins. A study was made of the pro-
tease and fraction I protein of rice leaf blades.
Protease was extracted from active (second) leaf
blades with 0.1 M phosphate buffer (pH 7) with
5 mM glutathione. Its activity was highest in the
protein fraction that precipitates from solution
between 60 to 80 percent saturation with ammo-
nium sulfate. Optimum pH was 7.0. Disc electro-
phoresis of the fraction indicated that protease
corresponds to protein bands of intermediate
to high mobilities. No difference in electro-
phoretic pattern was noted in the protein
isolated from plants at maximum tillering,
panicle initiation, and booting stages.
Fraction I protein constitutes 45 to 50 percent
of the soluble chloroplastic protein of vascular
plants. It contains the central enzyme in photo-
synthetic CO2 fixation of the rice plant-ribulose
1,5-diphosphate (RuDP) carboxylase. Workers
elsewhere have been able to crystallize fraction I
protein from tobacco leaves by dialysis against
water. We tried such a procedure on IR20 leaf
blades. Ammonium sulfate fractionation showed
that the fraction precipitating between 20 to 40
percent saturation with ammonium sulfate had
56 percent higher RuDP carboxylase activity
than the crude extract. Disc electrophoresis
showed that fraction I protein contains two
major bands. Loss of RuDP carboxylase activity
of fraction I protein after freeze-drying the fresh
leaf blades was associated with the loss of the
slower migrating band. Storage of the crude
extract for more than 4 days at -20'C also
caused this slower migrating band to precipitate.
The ammonium sulfate fraction was desalted

in Sephadex G-25, concentrated by treatment
with polyethylene glycol, and induced to crys-
tallize by dialysis against dilute buffer. No
crystals formed from fraction I protein of rice
indicating that it is albumin-like, in contrast
with fraction I protein of tobacco which is
globulin-like and hence becomes insoluble and
crystallizes out as salt concentration decreases
slowly during dialysis.
Resistance to brown planthopper. Studies with
IRRI entomologists on the isolation of a
chemical factor in rice plants for resistance to the

12 IRRI ANNUAL REPORT FOR 1973

brown planthopper (Nilaparvata lugens) were
continued. Attempts to air-dry plants on large
scale caused a large decrease in recovery of the
factor compared with extraction from fresh
tissues. Methanol (50%) extracts of Mudgo x
IR8 plants continued to show higher activity on
brown planthoppers than extracts of IR8. Hot
extraction gave higher recoveries than cold
extraction, but the difference in activity between
IR8 and Mudgo x IR8 extracts was reduced.
Hopperburn. Further studies were made with
IRRI entomologists on the changes in leaf blades
and sheaths which occur during brown plant-
hopper infestation, using Taichung Native 1
seedlings. In experiments using nondestructive
methods, the moisture content of the active leaf

blade dropped from 76 percent to 62 percent
during 5 days infestation, as measured by the
#-gauging method. The amount of honeydew
collected daily from the feeding insects and its
content of sugars and amino acids were variable.
Total amino acid, particularly proline level, was
higher in leaf blades of infested plants than in
leave blades of control plants. Nondestructive
methods-f-gauging, leaf diffusive resistance,
and leaf temperature-were less sensitive than
chemical measures such as proline content for
indicating stress in the plants. Leaf blades of
rice plants subjected to water stress by IRRI
agronomists have also shown higher proline
content.

CHEMISTRY 13

n u l ti p le The cropping systems program is
p using the resource utilization ap-
c ro p p n gl proach to develop more efficient
and productive cropping patterns
for the Southeast Asian rice farmer. Using this model, "small farm"
technology has been studied to find possible clues as to how technology
may be directed toward the small farmer. Traditional intercropping
systems with corn using mung bean, soybeans, sweet potatoes, peanuts,
or upland rice were 30 to 60 percent more productive with good
management and up to 100 percent more productive as various factors
became limiting. D Studies on plant interrelationships showed that the
balance of saturated systems depended on plant populations, while
productivity was affected by level of management and crop arrange-
ment. Traditional intercropping patterns have a more efficient light
utilization pattern and some have a higher efficiency of utilization of
applied nitrogen. This aspect may be of use in maximizing returns from
fertilizer. Insect relationships in traditional patterns continued to show
a high level of natural stability. This stability can be maintained in
intensive patterns with careful use of insecticides, but can be lost, and
the problems even aggravated if insecticides are not used at the proper
times and in the right amounts. O Weed research centered around the
management of weed communities to avoid shifting toward difficult-
to-control grasses and sedges with intensified cropping. The control of
crop leaf area index coupled with proper management techniques has
potential for this control. O Comparisons of power sources showed
that hand labor, small tractor, and carabao were similar from an
economic standpoint. The biggest differences were in the speed of
accomplishing the work. Hand or animal power had a lower potential
for increased cropping intensity because of this time factor. Efficiency
of energy production did not vary widely between sources. The energy
value of cash inputs was three times that of the actual power source.

CROPPING SYSTEMS PROGRAM
We are developing improved and intensified
cropping patterns to increase the welfare of rice
farmers in Southeast Asia. Cropping systems
technology is being organized to use farmers'
resources more efficiently in meeting this goal.
Multiple cropping-growing more than one
crop on the same piece of land in 1 year-is the
most common method.
A small, or "disadvantaged," or "poor"
farmer, typified by the average Asian rice farmer,
sells only a small share of what he produces
because his land holding is too small, because he
lacks other production resources, or because he
lacks technology, or, more often, a combination
of the three may apply.
We are striving to develop technologies
adapted to specific farm types, which are
grouped by the degree to which a farmer
participates in a market economy as well as by
his physical resources.

LESSONS FROM TRADITIONAL
TECHNOLOGY
In the process of developing cropping systems
technology for the "small" farmer we examine
his current cropping practices to see if clues can
be found as to how his lot may be improved. The
Javanese small farmer serves as our model. We
find him using labor-intensive methods to grow
several field crops in various combinations, both

A. Dominant crop harvested first

Corn

Peanut, sweet
potato or rice

B. Dominant crop harvested lost

Corn

Mung or
soybeans

I I I I I
0 I 2 3 4
Months
1. Common types of intercropping patterns.

with natural rainfall and with irrigation, in a low
cash-input situation. The widespread use of
these practices by small farmers (throughout the
tropics) leads us to wonder about their efficiency
in meeting their needs. The often-used practice
of intercropping has been chosen for study under
our resource utilization model. Its biological
as well as resource-use characteristics have been
evaluated.
Types of intercropping. We have investigated
two types of annual-crop intercropping patterns.
The first, which is most widely used by farmers,
includes a tall-growing (dominant) crop and a
shorter statured secondary crop. The dominant
crop is harvested first. The second configura-
tion also has a dominant and a secondary crop,
with the secondary crop being harvested either
at the same time as the dominant crop or earlier
(fig. 1).
Productivity. Total productivity is a basic
consideration in evaluating crop combinations.
Based on yields from several replicated trials,
crop combination can increase land productivity
from 30 percent to 60 percent over monoculture
cropping (Table 1). The land equivalent ratio
(LER) is the total land required using mono-
culture to give total production of the same crops
equal to that of 1 hectare of intercrop. It is
calculated by determining the ratio of the yield of
a crop in a mixture to its yield in monoculture
under the same management (weeds, fertility,
etc.) level. The optimum monoculture popu-
lation is used for comparison. The ratios of all
crops in the mixture are then added to give the
land equivalent. For example in a corn-soybean
intercrop (Table 2), corn yielded 5.28 t/ha and
the soybeans yielded 0.85 t/ha. The monoculture
yields (at optimum populations, but at the same
management level) were 5.52 t/ha for corn and
2.33 t/ha for soybeans. The ratios of intercrop
yields to monoculture yields were 0.96 for corn
and 0.36 for soybeans. The sum is 1.32. Total
productivity is thus 32 percent higher, and the
land equivalent is 1.32 hectares.
These results indicate that during the dry
season under irrigation, intercropping (alternate-
row planting) is usually more productive than
monoculture.
Wet season (rainfed) trials in a farmer's field
showed similar results from corn-rice inter-

16 IRRI ANNUAL REPORT FOR 1973

CROPPING SYSTEMS PROGRAM
We are developing improved and intensified
cropping patterns to increase the welfare of rice
farmers in Southeast Asia. Cropping systems
technology is being organized to use farmers'
resources more efficiently in meeting this goal.
Multiple cropping-growing more than one
crop on the same piece of land in 1 year-is the
most common method.
A small, or "disadvantaged," or "poor"
farmer, typified by the average Asian rice farmer,
sells only a small share of what he produces
because his land holding is too small, because he
lacks other production resources, or because he
lacks technology, or, more often, a combination
of the three may apply.
We are striving to develop technologies
adapted to specific farm types, which are
grouped by the degree to which a farmer
participates in a market economy as well as by
his physical resources.

LESSONS FROM TRADITIONAL
TECHNOLOGY
In the process of developing cropping systems
technology for the "small" farmer we examine
his current cropping practices to see if clues can
be found as to how his lot may be improved. The
Javanese small farmer serves as our model. We
find him using labor-intensive methods to grow
several field crops in various combinations, both

A. Dominant crop harvested first

Corn

Peanut, sweet
potato or rice

B. Dominant crop harvested lost

Corn

Mung or
soybeans

I I I I I
0 I 2 3 4
Months
1. Common types of intercropping patterns.

with natural rainfall and with irrigation, in a low
cash-input situation. The widespread use of
these practices by small farmers (throughout the
tropics) leads us to wonder about their efficiency
in meeting their needs. The often-used practice
of intercropping has been chosen for study under
our resource utilization model. Its biological
as well as resource-use characteristics have been
evaluated.
Types of intercropping. We have investigated
two types of annual-crop intercropping patterns.
The first, which is most widely used by farmers,
includes a tall-growing (dominant) crop and a
shorter statured secondary crop. The dominant
crop is harvested first. The second configura-
tion also has a dominant and a secondary crop,
with the secondary crop being harvested either
at the same time as the dominant crop or earlier
(fig. 1).
Productivity. Total productivity is a basic
consideration in evaluating crop combinations.
Based on yields from several replicated trials,
crop combination can increase land productivity
from 30 percent to 60 percent over monoculture
cropping (Table 1). The land equivalent ratio
(LER) is the total land required using mono-
culture to give total production of the same crops
equal to that of 1 hectare of intercrop. It is
calculated by determining the ratio of the yield of
a crop in a mixture to its yield in monoculture
under the same management (weeds, fertility,
etc.) level. The optimum monoculture popu-
lation is used for comparison. The ratios of all
crops in the mixture are then added to give the
land equivalent. For example in a corn-soybean
intercrop (Table 2), corn yielded 5.28 t/ha and
the soybeans yielded 0.85 t/ha. The monoculture
yields (at optimum populations, but at the same
management level) were 5.52 t/ha for corn and
2.33 t/ha for soybeans. The ratios of intercrop
yields to monoculture yields were 0.96 for corn
and 0.36 for soybeans. The sum is 1.32. Total
productivity is thus 32 percent higher, and the
land equivalent is 1.32 hectares.
These results indicate that during the dry
season under irrigation, intercropping (alternate-
row planting) is usually more productive than
monoculture.
Wet season (rainfed) trials in a farmer's field
showed similar results from corn-rice inter-

16 IRRI ANNUAL REPORT FOR 1973

Table 1. Land equivalent ratio (LER) under good man-
agement for five crop combinations with corn (95-day
maturity). IRRI, 1973 dry season.

Crop Maturity (days) LER
Dry soybeans' 90 1.3
Green soybeans0 65 1.6
Mung beanb 60 1.5
Sweet potato 120 1.5
Peanutb 110 1.6

*From a single management level, four replications. bAvg of
four levels of weed management, three nitrogen levels, and
eight corn populations and row spacings.

Table2. Effect of intercropping field corn in soybeans.*
IRRI, 1973 dry season.

Crop
combination

Grain yield" (t/ha)
Corn Soybean LER

Soybean alone 2.33
Field corn alone 5.52 -
Soybean + field cornd 5.28 0.85 1.32

'Variety Thai Early Composite (87-day maturity). bVariety
Multivar 80 (85-day maturity). CMeans of four replications.
dl -m spacing.

cropping (Tables 3 and 4). IRRI trials of
intercropping patterns have thus shown that
under Los Bafios conditions, with highly pro-
ductive improved varieties having approximately
the same growth duration as farmer's varieties,
intercropping makes better use of a farmer's
land resources. A higher return on cash inputs
may even be possible (Table 5).
Plant spacing and time of planting. The timing
of the overlap period and the crop configuration
(row spacing, population) are important to the
success of these patterns. In our trials, both crops
in the combinations were planted at the same
time. With corn-mung, the mung reaches the
flowering stage (30 to 35 days after planting)
before being shaded by corn. The yield reduction
in the mung (as compared with monoculture) is
usually about 50 percent if nothing hinders the
mung growth relative to that of corn. If mung is
planted after corn it will not yield well because of
its sensitivity to shading in the seedling stage.
Since mung usually covers the ground rapidly it
would not be effective to plant corn later because
the corn is equally sensitive to shading in the
seedling stage.
The total productivity of corn-mung when
planted together is rather independent of the

corn population. We have plotted corn and mung
yields as a fraction of their monoculture checks
(at the same management level) for several levels
of weed control and'fertility in figure 2. Points
on a curve represent differences in corn popula-
tions only. As corn population increases, its
yield increases and the mung yield decreases in a
linear fashion (as shown by the high r values).
The diagonal lines labeled with percentage fig-
ures show the relative increase in productivity
over the monoculture check (lines of equal
LER). At 270 kg/ha of nitrogen and with weed
control (1.5 kg/ha a.i. of butachlor) the advan-
tage of intercropping remained 20 to 30 percent
above monoculture. Only with no weed control

Table 3. Yield and gross returns from upland rice-corn
intercropping. Farmer's field, Laguna, Philippines, 1973
wet season.

Yielda Value
Crop (t/ha) (P/ha)
Corn (Thai Early Composite) 4.3 4300
Rice (IR442-2-58) 3.9 3100
Corn and 4.0
rice 2.2 5800
Corn (Penjalinan) 1.7 1710
Rice (IR442-2-58) 3.8 3055
Corn and 1.4
rice 3.4 4134

'At the best management level.

Table 4. Corn (Early Thai Composite, 85-day maturity)
and rice (IR442-2-58, 120-day maturity) intercropped
at varying levels of nitrogen. Farmer's field, Laguna,
1973 wet season (avg of four replications).

Yield (t/ha)
Crop d ( ) Total value
Rice Corn (P/ha)'
60 kg/ha N
Corn 3.9 3900
Rice 4.2 3300
Rice and corn 1.5 2.9 4100
120 kg/ha N
Corn 4.0 4000
Rice 4.4 3500
Rice and corn 2.2 2.8 4600
180 kg/ha N
Corn 4.3 4300
Rice 3.9 3100
Rice and corn 2.2 4.0 5800
240 kg/ha N
Corn 4.4 4400
Rice 3.0 2400
Rice and corn 2.0 3.4 4900

0 P804/t of rice, P1000/t of corn.

MULTIPLE CROPPING 17

Corn yield in intercropping as a fraction of
its monoculture check

N No weed control, 180 kg/ha N
( r= -0984*) and 270 kg/ha N
1.6 (r=-0.997*)
1

SWeed control, 180 kg/ha N
S% (r=-998**)
1.2 Weed control, 70 kg/ha N
1.2 ( r -0.953* )

Weed control + +60
270 kg/ho N
0.4 (r=-0.978*)

+40%
+20%

0 02 0.4 0.6 0.8 10 1.2
Mung yield in intercropping as a fraction of its monoculture check
2. Relations between the yields of corn and mung in an
intercrop combination as a result of different corn row
spacings and populations at three levels of nitrogen and two
levels of weed control. IRRI, 1973 dry season.

and high nitrogen levels was there a marked
increase in productivity with increasing corn
population. Although the relative advantage of
intercropping is greater under low management
than it is at high management (100% vs. 30 to
40%) the actual productivity may be lower
(Table 6).

Table 5. Peso return per peso of added nitrogen in
corn-rice intercropping. Farmer's field, Laguna, 1973
wet season (avg of four replications).

Nitrogen increment
(kg/ha)

Return (P/ P added nitrogen)
Rice alone Corn alone Intercrop

60-120 2.2 1.1 5.6
120-180 -4.4 3.3 13.3
180-240 -7.8 1.1 -10.0

The normal crop configuration used by farm-
ers, when mixing crops, is to plant a solid stand
(as in monoculture) of the low-statured "minor"
crop and then introduce the major crop at vary-
ing populations and row spacings. We have
followed this practice in the intercrops of corn
with mung, soybean, peanut, sweet potato, or
rice. Although the time of planting should be the
same for corn and mung, with corn-soybean, the
soybeans start more slowly and a delay in the
planting of corn seems beneficial (fig. 3). When
DMR-2 corn was planted 20 days after soybeans
(Shih Shih) and the soybeans were harvested as a
green vegetable, the productivity of the combina-
tion was 102 percent higher than that of either
crop alone and 80 percent higher when harvested
dry as shown by LER values of 2.02 and 1.8
respectively (fig. 3). The 20-day delay allowed the
soybeans to get a start before being shaded by
the faster growing corn.
Physiology of intercropping. When the growing
and reproductive stages of both crops coincide,
as with combinations such as corn-mung and
corn-soybeans, and when the populations of
both crops are high, the relationship between
the yields of the two crops is linear at a nearly
constant level of productivity for a given man-

Table 6. Return per hectare for corn-mung intercropping averaged over corn-plant populations (after deducting the
cost of nitrogen). IRRI, 1973 dry season.

Return (P/ha)
CropO 70 kg/ha N 180 kg/ha N 270 kg/ha N

No weeding Weed controlc No weeding Weed control No weeding Weed control
Corn alone 920 2280 1730 2130 2050 3510
Mung alone 2490 2530 1980 2590 2190 2870
Best intercrop combination 3580 3420 3490 3580 4220 4530
Mean of all inter-
crop combinations 2860 3280 2980 3500 3470 3930

'Corn variety, DMR2 (97-day maturity). Mung variety MG50-10A (65-day maturity). "Corn = P0.79/kg. Mung = P2.25/kg. CButa-
chlor at 1.5 kg/ha a.i.

18 IRRI ANNUAL REPORT FOR 1973

Fraction of monoculture check
1.2 Dry sovb

01
Soybean LER
2.2 I

Soybeans 80 60 40 20 0
alone
Days of delay
3. Effect of time of delay of corn planting in corn-soybean
intercrop. IRRI, 1973 dry season.

agemnent level. In other words, productivity is
maximized at that level of light, water, nutrients,
and other resources in the experiment for that
given crop combination. Sweet corn-mung at
high fertility with complete weed control illus-
trates the principle. As the corn population is
changed, the relationship between corn and
mung yield is linear at a productivity level 27
percent above that of the monoculture checks
(fig. 4). A static and an "unsaturated" produc-
tivity are both illustrated by the corn-soybean
interrelationship (fig. 5). When planted at the
same time, the productivity was 40 percent above
monoculture. Corn was favored at 1-meter row
spacing of the corn; the balance shifted towards
soybeans at the 2-meter row spacing with pro-
ductivity remaining constant. A 20-day delay in
corn planting resulted in a new relationship with
an 80-percent increase in productivity.
The relationships do not seem to hold as

Corn yield as a fraction of
its monoculture check
1.0 I \

0 0.2 0.4 0.6 0.8 1.0
Mung yield as a fraction of its monoculture check
4. Relations between yields of sweet corn and mung in
intercrop combinations under different corn populations
(with mung population remaining constant). IRRI, 1973
dry season.

closely when the growing periods have less over-
lap, as with corn-sweet potato (fig. 6).
The corn-rice system is of particular interest
because of its widespread use. Two experiments
were conducted to study its crop-interrelation-
ship effects. The Indonesian corn variety Pen-
jalinan (70-day maturity to dry corn) was used
with IR442-2-58 rice. These varieties fit the
usual maturity pattern for this combination in
farmer's fields. The two crops are planted to-
gether and the corn is mature just before the rice
flowers. The rice is not appreciably shaded by the
corn until about the maximum tillering stage so
the period of maximum competition occurs
during the time when rice is least sensitive to
shading.
In the first experiment the area in rice was 43
percent, 71 percent, or 100 percent (solid plant-
ing of rice with corn added in addition) with each
of three corn populations and two row spacings.
At most corn populations and row spacings, a
larger rice area increased total productivity
without a corresponding decrease in corn yield
(fig. 7). This indicated that the system was not
saturated (at its maximum total productivity

MULTIPLE CROPPING 19

Corn yield os a fraction of
its monoculture check

0 0.2 0.4 0.6 0.8 1.0 1.2
Soybean yield as a fraction of its monoculture check
5. Effect of intercropping corn and soybeans with different
length of delays in corn planting after soybeans were planted.
IRRI, 1973 dry season.

Corn yield as a fraction of
its monoculture check

0 0.2 0.4 0.6 0.8 1.0 1.2
Sweet potato yield as a fraction of its monoculture check

level) except at the 43,000-corn population at
1.4-m row spacing. The absolute productivity at
saturation obviously depends on the productive
capacity of the varieties. Table 3 shows the yield
range for Penjalinan in rice as compared with
that of Thai Early Composite. The total pro-
ductivity of the two different combinations was
about the same but was arrived at in different
ways. The productivity of Penjalinan was low,
but the rice compensated for it. This short-
statured corn variety detracted little from the
rice yield; every kilogram of corn yield was a
bonus. With Thai Composite the rice yield
decreased more but the corn was higher yielding.
In another experiment the area in corn and
in rice was 50 percent each. This proportion was
too little to approach saturation for the mixture.
The planting arrangements were 15 rows of rice
alternating with 3 rows of corn, 9 rows rice with
2 rows corn, 5 rows rice with 1 row corn, or 2
rows rice with 1 row corn (in this arrangement
the corn was at equidistant spacing). The objec-
tive was to test the hypothesis that the advantage
of intercropping (in a compatible combination)
is derived from achieving maximum contact
between species. In our experiment the contact
between species was maximized with equidistant

0.2 0.4 06 0.8
Rice yield as a fraction of its monoculture check

6. Effect of corn population and management level on the 7. Effect of corn population, row spacing, and proportion of
productivity of corn-sweet potato intercrop. IRRI, 1973 dry the area in rice on intercrop productivity. IRRI, 1973 wet
season, season.

20 IRRI ANNUAL REPORT FOR 1973

Table 7. Effect of row arrangement on the gross return
from corn-rice intercropping with each crop occupying
50 percent of the area. IRRI, 1973 wet season.

Return' (P/ha)
Crop ow Corn population (plants/ha)
arrangement
15,000 60,000
Corn alone Solid stand 710 1400
Rice alone Solid stand 2380 2380
Corn-rice
3 x 3b" 15 rice x 3 corn 1560 1580
2 x 2c 9 rice x 2 corn 1540 1940
1 x 1e 5 rice x 1 corn 2160 3080
1 x Id 2 rice x 1 corn 3590 3160

aCorn at P1.00/kg. Rice at P0.80/kg. bThree beds of rice
alternated with three beds of corn. Cl.4-m row spacing for
corn. d0.7-m rows for corn.

corn spacing (two rows of rice with one row of
corn) at the low corn population.
Productivity increased with increasing contact
between the corn and rice (fig. 8). The 80-percent
gain in productivity when half of the area was
covered with rice, and corn was planted at 15,000
plants/ha (when compared with solid corn at
60,000 plants/ha and a full stand of rice) was
surprising. It is evident that in corn-rice, the
timing of the overlap of these varieties seems to
be optimum, but we did not expect that the
increasing contact between species would show
such dramatic results. The gross return from
these yields confirms the trend (Table 7).
Light interception. At least part of the differ-
ences in performance between monoculture and
intercropping can be explained by differences in

Corn yield as a fraction of
its monoculture check
1.2 \

0 2 4 6 8 10
Rice yield os o fraction of its monoculture check
8. Effect of row arrangement on productivity of corn-rice
intercrop with each crop planted to 50 % of the area (r = rows
of rice, c = rows of corn). IRRI, 1973 wet season.

light interception. Intercropped combinations
usually have a higher total light interception
(Table 8) as well as a more efficient pattern over
the entire season. They thus appear to make
better use of light resources.
Weed response. Light interception also parti-
ally explains the differences in weed response

Table 8. Light transmission of various crop canopies. IRRI, 1973 dry season.

Transmitted lights (%)
Corn Corn-row
population spacing Above lower canopy Ground level
(103 plants/ha) (m) 44 DSb 63 DS 30 DS 44 DS 63 DS

Corn 40 1 52 32 26
Corn 20 2 77 57 45
Peanut 60 21 9
Mung 49 12 23
Sweet potato 66 45 9
Peanut-corn 40 1 32 30 35 11 4
Peanut-corn 20 2 61 45 37 8 5
Mung-corn 40 1 38 22 28 6 8
Mung-corn 20 2 60 49 36 10 15
Sweet potato-corn 40 1 40 21 34 17 18
Sweet potato-corn 20 2 53 48 36 11 5

'Calculated from a weighted mean of several sampling points across the rows at ground level integrated over a 24-hour period. bDays
after seeding.

MULTIPLE CROPPING 21

seen in intercrop plantings. Mung bean by itself
is less responsive to weed control than corn alone
(Table 9). The corn-mung intercrop has little
response to weed control because the mung sup-
presses the weeds, and the total productivity is
higher. The ability of mung to compete with
weeds, however, depends both on the growing
conditions and the type of weeds. Wet weather
and low light intensities reduce early mung
growth and favor growth of weeds. In the dry
season with high light intensities and a pre-
dominance of annual grasses and sedges which
are shade-sensitive, the effect of mung on weeds
is dramatic. This plant-weed competition, how-
ever, is markedly influenced not only by the type
of crops in the combination, but by fertility level.
The actual weed response interaction with
crop and nitrogen level is shown in figure 9.
Weed yields did not increase significantly under
corn as nitrogen level increased. The increase
with mung was slight, but peanut failed to sup-
press weeds at high fertility levels. Within crop
combinations a higher population still lowers
weed growth(Table 10). The interactions of crop

Dry weed wt (t/ha)

Corn Peonut Corn + Mung Corn +
Peanut Mung
9. Interaction effects of crop combination, weed control,
and fertilizer level on weed weight. IRRI, 1973 dry season.

Table 9. Gross returns for corn, mung. and corn-mung
intercrop averaged over corn populations and nitrogen
levels. IRRI, 1973 dry season.

Gross return (P/ha) Increase
Crop No weed Weed (%)
control control'
Cornm alone 1300 2450 88
Mungb alone 2480 2930 18
Corn and mung 3370 3920 16

PO.79/kg. bP2.25/kg. CButachlor at 1.5 kg/ha a.i.

Corn borer infestation normally begins with
egg-laying moths which select fields by, perhaps,
the sight and smell of host plants. To examine the
effect of visual stimuli, we placed brown or green
burlap between rows in corn plots. We found that
the moths preferred corn plots with green inter-
row cover less than those with brown inter-row
combination with nitrogen level are also import-
ant for weed control (fig. 10). Gross returns are
always higher from intercrop combinations but
the returns from weed control depend both on
the population of corn and the nitrogen level.
Traditional crop combinations thus have
definite weed competition properties, partly
resulting from their light interception patterns.
Crop combinations and insect interactions.
Earlier IRRI findings that the traditional inter-
cropping of peanut with corn decreased corn
borer infestation have led to more detailed
studies to determine the nature of the effect and
its possible use in modern intensive systems on
small farms. Three aspects of the borer's popula-
tion performance were examined: adult ovi-
position behavior, larval feeding and establish-
ment on corn, its principal host plant, and effects
and interactions of predation by spiders (Lycosa
spp.) and insecticidal treatments.

Table 10. The effect of corn population and spacing on
weed growth for different intercrop combinations at
intermediate nitrogen. IRRI. 1973 dry season.

Corn Corn row Dry weed wt (t/ha) in
Corn Corn row ----------
population spacing Mung Sweet potato' Peanutb
(10' plants/ha) (m) + corn + corn + corn
10 1 1.3 1.8
60 1 0.8 0.6 0.5
10 2 0.5 1.6 1.5
20 2 0.3 0.7 1.0

'Sweet potato alone, 1.8 t/ha of weeds. 'Peanut alone. 2.7
t/ha of weeds.

22 IRRI ANNUAL REPORT FOR 1973

100 200 300 400 500
Nitrogen level ( index)
10. Nitrogen response of corn, mung and their intercrop at
two levels of weed control (Nitrogen index: for corn, 50 kg/ha
N = 100; for mung, 20 kg/ha N = 100; for corn+ mung, 70
kg/ha N = 100). IRRI, 1973 dry season.

cover (Table 11). When peanuts were planted
between the corn rows with and without green
burlap, the corn plots with both peanuts and
green burlap had lower infestations than the
corn plots with only peanut, suggesting that the
moths responded to olfactory cues as well as
visual cues. The effects, however, diminished as
the plants grew older perhaps because of the
increasing spread of the corn canopy.
The survival and establishment of young,
first-instar larvae which were artificially intro-
duced on the plants were not influenced by the
peanut intercrop. That is, substances from pea-
nut in amounts toxic to feeding corn borer larvae
on corn are not evidently involved.
A preliminary survey in our experimental corn
fields revealed at least 19 kinds of spiders. Two
species of wolf spiders (Lycosa spp.) were the
most active and the most frequently observed
preying on various insect pests, including young
corn borer larvae. Trapping showed that wolf
spiders from neighboring fields move more fre-
quently towards corn plots with a peanut inter-
crop than to plots without the intercrop (Table
12). Within the corn field, however, the spiders
moved from one plot to the other at more or less
equal frequencies.
To assess the effects of spider predation and

Table 11. Influence of green and brown visual cues on
oviposition preference of the corn borer (based on
examination of 50 plant samples, avg of two repli-
cations). IRRI, June-September. 1973.

Borer egg masses on corn
Color of inter-row (no./100 plants) Decrease
burlap cover Corn alone Corn with
peanut
29 days after seeding
None 13 6 54
Brown 14 5 64
Brown and green strips 11 6 45
Green 8 6 25
35 days after seeding
None 16 2 88
Brown 46 21 54
Brown and green strips 27 22 19
Green 27 19 30
42 days after seeding
None 58 26 55
Brown 44 38 14
Brown and green strips 49 43 12
Green 46 42 10
52 days after seeding
None 42 42 0
Brown 38 30 21
Brown and green strips 50 51 0
Green 51 45 12

Table 12. Comparison of spider (Lycosa spp.) influx and
preference for solid corn stand or corn-peanut inter-
crop. IRRI, June-September, 1973.

Spir Spiders' (no.)
Spider
movement Corn alone Corn with
peanut
39-43 days after seeding
From neighboring fields (influx)b 30 32
Within field (preference)c 33 32
45-51 days after seeding
From neighboring fields (influx)b 35 58
Within field (preference)c 30 30
52-58 days after seeding
From neighboring fields (influx)b 34 48
Within field (preference)c 28 26

*Avg of four plots, each 12 x 24 m. bCatches of 20 traps set
at both ends of corn rows. CCatches of 20 traps set between
corn alone and corn-peanut plots.

its interaction with the effects of peanut inter-
cropping, borer infestation was compared
among plots in which spider predation was mini-
mized by a spider barrier (20-cm-high plastic
wall) and parathion sprays at planting and 1
week later, or encouraged by allowing free
spider movement and not treating the field with
insecticides. We found that spider predation con-

MULTIPLE CROPPING 23

Table 13. Effects of peanut intercropping and spider
predation on corn borer infestation. IRRI, 1973 wet
season.

Borer infestation'
(no./100 plants)
Borer stage (no.0 plants) Decrease
and damage Without With (%)
peanut peanut
intercrop intercrop
Spider predation minimized
Egg masses' 21 16 21
Larvae-pupae-pupal cases 69 50 27
Pupal cases only 53 36 33
Tunnels in stalks 115 109 6
Spider predation encouraged
Egg masses 10 7 23
Larvae-pupae-pupal cases 80 49 39
Pupal cases only 58 28 52
Tunnels in stalk 115 89 22

aAverage of eight replications: egg mass data based on exami-
nation of 120 to 160 plants per replication at 28 days after
seeding. bFrom dissection of portion of stalk below ear of 30
sample plants per replication at harvest (88 days after seeding).

tribute to the decreased borer infestation
(Table 13). Thus the beneficial effect of the pea-
nut intercrop was enhanced by encouraging the
activities of predatory spiders. On the other
hand, the regular use of the broad-spectrum
insecticide, azinphosmethyl, diminished these
benefits; even the use of the more selective bio-
logical insecticide, Bacillus thuringiensis, was
detrimental but not as much as the nonselective
insecticide (Table 14). Evidently, to maintain
and encourage beneficial effects of intercropping
on insects as management levels are increased,
considerable planning and judicious insecticide
treatments are required. Proper timing and
placement of insecticides seem to be the more

Table 14. Influence of insecticide treatments and spider
predation on decrease in corn borer infestation from
corn-peanut intercropping. IRRI, 1973 wet season.

Change due to peanut intercropping' (%)
Treatment Survival
Adult
ovipositionb Late instar' Early instard
Azinphosmethyle -10 9 -12
B. thuringiensis' -42 -13 -18
No insecticide -51 -26 -32

aFrom paired comparison of plots, 12 m x 24 m each, of corn
alone and corn-peanut intercrop; corn population, 40,000/ha.
bEgg masses counted at 28, 35, and 40 days after seeding.
cFeeding lesions on whorl leaves counted at 28, 35, and 40
days after seeding. dFeeding holes on stalks counted at 48, 55,
and 62 days after seeding. e0.05% a.i. solution. 'Dipel applied
22, 23, and 38 days after seeding.

feasible approaches. Results of our studies indi-
cate that one spray treatment with Orthene
(O-S-dimethyl N-acetyl phosphoramido-thio-
ate), a broad-spectrum insecticide, at 35 to 45
days after seeding had little or no detrimental
effects, while one insecticide application at 30
days after seeding with or without additional
treatments later markedly diminished, if not
completely nullified, these benefits (Table 15).
Economic implications. Our data on the
economic returns from intercropping have come
from preliminary trials on the IRRI station.
Initial results indicate that the relative profita-
bility of monoculture and intercropping depend
on the management level or on the general grow-
ing conditions. With a high level of management
and good growing conditions, monoculture
seems to give better returns above variable costs
(Table 16). Return per hectare per day is about
the same, but return per unit of labor is higher
with monoculture. At lower management levels,
or where heavy rains or wet soil conditions re-
strict crop growth, intercropping appears super-
ior for total return above variable costs, return
above variable cost per hectare per day, and
return per unit of cash expense. It is about the
same as monoculture in return per unit of labor.
The amount of labor used is higher in intercrop-
ping. It seems likely, based on very limited data,
that intercropping may best fit in land-limiting,
labor-surplus situations. It also may be far more
productive under situations where management
is less than optimum for monoculture.

Table 15. Influence of time of insecticide application
(Orthene at 0.05% a.i.) on the effect of corn-peanut
intercropping on corn borer infestation. IRRI. 1973 wet
season.

Change in
Date of spraying larval feeding holes in
stalk due to peanut inter-
29 DS 36 DS 44 DS 50 DS
croppingb (%)
/ 24
/ -- --22
-36
/ -17
/ -19
/ / 25
S / / / 6
S -25

oDays after seeding. 'From paired comparison of plots. 5 x 6 m
each, of solid corn stand and corn-peanut intercrop, mean of
readings at 50, 57, and 72 days after seeding.

24 IRRI ANNUAL REPORT FOR 1973

Table 16. Return over variable costs for monoculture and intercropping under high (H) and low (L) pest and water
management levels. IRRI. 1973 dry season.
Return over variable cost (P/ha)
Crop Per peso of
Total Per day Per man-day cash expense
H L H L H L H L

Dry corn 3340 2340 34 24 110 82 4.40 2.40
Mung 1440 840 19 11 17 12 1.50 0.90
Peanut 3500 1000 32 9 58 21 3.20 0.90
Sweet potato 4530 3390 38 24 49 38 4.70 3.50
Avg 3200 1890 31 17 58 38 3.40 1.90
Peanut and dry corn 3510 3870 32 35 63 67 2.70 2.90
Peanut and green corn 4330 3750 36 31 39 35 5.10 4.40
Mung and green corn 370 1310 5 19 9 15 0.30 1.00
Sweet potato and green corn 4590 3340 42 30 75 56 3.40 2.50
Sweet potato and dry corn 2950 5440 25 45 28 47 3.40 6.30
Avg 3150 3530 28 32 43 38 3.00 3.40

VARIETAL TESTING OF COMPONENT CROPS

Mung bean. During the year, 476 mung lines
from India and from the U.S. world collection
were added to our collection, bringing the total
to more than 600. The best 12 lines from two
seasons of testing were compared in solid stands
and also interplanted in corn (Table 17). The
Philippine varieties MG50-10A and CES 55
continued to yield well in solid stands as well as
when interplanted in corn. Interplanting did not
change the time to flowering, but caused the
plants to grow taller, to have heavier infestation
of leaf disease, to have fewer pods, and to be-
come senescent earlier (Table 18). Seed size was
reduced only slightly. The interplant trials were
grown with 40,000 plants/ha of Early Thai Com-
posite corn at a high fertility level, shifting the
balance in favor of corn. Data from other trials
indicate that a decreased corn population would
not change overall productivity but would shift
the balance in favor of mung. Testing mung
varieties under a corn population that would
allow mung to yield 50 to 60 percent of that in a
pure stand would probably show varietal differ-
ences better than the 37-percent average that was
achieved for the 18 varieties we tested (Table 18).
Soybean. Of the soybean varieties previously
tested, Multivar 80 continued to yield well
(Table 19). Two new breeding lines from the
University of the Philippines at Los Bafios
(UPLB) College of Agriculture, CES 16-103 and

CES 16-23, were high yielding but susceptible to
disease. CES 16-103 has an excellent plant type
with a stiff, erect stem. Thirty vegetable soybean
types were introduced from soybean breeding
stations in Japan. Several were early and yielded
well. The lines have high protein and low oil
content and should have less viability problems
in the tropics than the types with higher oil levels
from temperate areas. Most of them are early
maturing and short statured. Economic data
show that stiff-stemmed, short-statured types
can be harvested as a green vegetable by cutting
the top leaves and the stem at ground level and
marketing the whole stem for an extremely high

Table 17. Highest yielding mung bean varieties. IRRI,
1973.

Variety

CES 28
MG50-10A
M 350
CES 55
M 198
MD 15-2
S-8 (yellow)
MG50-10A (yellow)
M 304
M 79
M 205
M 157

Yields
(no corn)
(t/ha)
1.70
1.60
1.59
1.58
1.56
1.55
1.53
1.41
1.39
1.37
1.29
1.24

Relative yield when
planted in corn
(%)
28
36
24
37
33
26
24
42
41
40
43
41

'Mean yields from two seasons of replicated trials.

MULTIPLE CROPPING 25

Table 18. Response of 18 mung bean varieties to inter-
cropping in corn. IRRI, 1973 dry season.

Character Mung With
Characr alone corn
Yield (t/ha) 1.5 0.6
Time to flowering (days) 31.1 31.2
Maturity (days) 63.4 55.8
Height (cm) 65.2 72.4
Pods (no./plant) 11.6 5.0
1000-seed wt (g) 53.5 49.2
Cercospora and rust, 3.8 4.5
Lodging 2.4 2.4

'1 = slight, 5 = severe. 1 = little, 5 = heavy.

return. Protein production per day as well as
per unit of labor is high.
Cowpea. Two groups of cowpea accessions
were tested. Of 18 breeding lines and accessions
from UPLB several appeared promising (Table
20). From 143 lines received from the Asian
Vegetable Research and Development Center
in Taiwan, 13 appeared to have promise. The
lines were tested in an early rainy season plant-
ing when light intensity was low, tending to make
the varieties viny and indeterminate. That per-
haps explains why few of these lines looked good.
Cowpea is the crop in our systems with the
greatest need for varietal improvement. The
lack of determinate growth habit and suscepti-
bility to virus and soil-borne disease limit its
usefulness in intensive systems.
Sweet potato. In trials of sweet potato varieties,
BNAS 51 was consistently superior under both
wet and dry conditions. In a time-of-harvest
trial, BNAS 51 yielded far better than Centennial
at all harvest times (fig. 11). The nitrogen level
necessary for high yield seems critical. Nitrogen
levels above 100 kg/ha reduced yield of tubers
even with intercropping. The required fertility
management of sweet potato intercrop combina-
tions thus appears to be quite different from that
of corn-rice or other combinations.
Corn. The key corn varieties we use are Thai
Early Composite and DMR-2, a 97-day maturity
variety from the Philippines. Thai Composite
developed black layer in 85 to 87 days. Its yield
potential is 6.5 to 7.0 t/ha in the dry season and
4.0 to 4.5 t/ha in the wet season under Los
Baiios conditions. DMR-2 is resistant to downy
mildew, but is later and has a lower yield
potential. Three Indonesian varieties, Pakelo,

Table 19. Highest yielding soybean introductions. IRRI,
1973 dry season.

Variety Yield* Maturity Plant Pods Rust
(t/ha) (days) ht (cm) (no./plant) rating
CES 16-103 2.94 80 51 34 3.8
Kuro-daizuc 2.94 109 120 71 4.0
Multivar 80 2.89 84 84 28 3.0
CES 16-23 2.70 90 108 44 2.2
Higo-daizu 2.39 70 46 30 1.0
Shiro-daizuc 2.30 98 114 48 4.0
Hsih Hsih 2.31 73 39 30 1.0
Ao-daizu 2.22 90 36 24 3.0
Kimusume 2.20 69 48 28 1.0
Shiro-hadaka 2.19 64 46 28 1.0
Clark 63 2.14 92 103 48 2.0
Aa-2002 2.10 72 38 25 2.0
Higo-musume 2.09 69 38 29 1.0
lyo-daizu 2.04 74 34 37 3.0
Gin-daizu 1.99 82 47 31 3.0
Ibaragi 1.95 70 34 23 1.0
Tainung 3 1.92 84 66 39 2.8
Fuji 1.90 68 42 27 1.5
Hachigatzu-daizu 1.85 80 42 23 2.5
Kailua 1.80 83 84 30 3.0
E.G. Special 1.68 78 70 29 4.0
TK5 1.58 80 66 41 3.5

'LSD (5%): 0.24. 1b = slight, 5 = severe. CSuitable for late
planting.

Binongko, and Penjalinan, were introduced and
increased. Penjalinan appeared to be the most
promising. It matures in around 70 days, pro-
ducing 3 t/ha in the dry season and about 2 t/ha
in the wet. Its only use appears to be in intercrop
combinations, but it is questionable whether the
10-day shorter growing period compensates for
the lower yield when compared with Thai Early
Composite. It fits better the growth cycle of rice
in intercropping than does Thai Early Compo-
site.

CROP MANAGEMENT TECHNIQUES
Ridge-and-furrow rice growing. A final year of
testing of the ridge-and-furrow method of grow-
ing rice strengthened the notion that it has little
application on the heavy Maahas clay soil of the
IRRI farm during the wet season. Early in the
1972 wet season, we began to prepare the soil in
an upland condition with broad furrows separa-
ted by narrow ridges at 1-meter spacing. On
September 7 after several aborted attempts at
land preparation, weed control, seeding, and
reseeding, a uniform stand of rice was finally
established. During July and August, each time
after the fields had been prepared and the rice

26 IRRI ANNUAL REPORT FOR 1973

Table 20. Growth characteristics and disease rating of the top cowpea accessions. IRRI, 1973 wet season.

Accession

Mecan pea
Red cowpea 6-1
Cowpea #18
Red cowpea #6-14
Cowpea #16
Red cowpea 6-12 W
Virginia 67-3
Cowpea #15
Cowpea #23
Cowpea #21
Cowpea # 14
Virginia crowder
Cowpea #33
Red cowpea
Cowpea #32
Red cowpea 6-12G
Cowpea #22

Growth Disease rating
character* Mosaic virus Wilt
SD 1 1
D 2 1
D 2 2
SD 1 2
D 2 2
D 1 2
D 2 2
D 1 2
D 1 1
D 2 2
D 1 2
D 2 3
D 2 3
SD 3 2
D 3 3
D 3 2
D 2 2

ISD = semi-determinate; D = determinate. 1b = no visible infection; 4 = heavily infected. CDays from seeding to last harvest of dry
seeds. dE = erect; SC = semi-creeper.

sown, the dry spell was broken by a heavy rain
which restricted rice emergence because of
waterlogged soil and a thinly puddled surface
layer. To have the precision of land preparation
required in this method it should be done with
irrigation before the rains start. The narrow
range of soil moisture that allows good work-
ability of Maahas clay limits the time when it can
be prepared once the rains start. On a lighter,
better drained soil the method may be feasible
either with irrigation in the dry season or at the
start of the monsoon.
In the trial, rice responded to nitrogen only
up to 100 kg/ha levels. There was a response to
seeding rate up to 90 kg/ha but only at nitrogen
levels below 100 kg/ha. Both IR8 and IR20
showed similar responses.
In a second trial, planted at the end of the
rains in November, the feasibility of using the
same ridge-and-furrow system, but puddling the
furrows, was tried in the hope that this might add
stability to the system during rainy periods. Here,
again, however, the problems of soil and water
management and weed control were extensive.
Weed control and management after planting
were complicated by having both upland and
lowland conditions in the same field. IR20 was
direct-seeded in all treatments, with three differ-
ent seeding methods on puddled furrows and
the standard three-row planting on the "upland"

type of ridge and furrow. Vegetables (cabbage
and Chinese mustard) were planted on the
ridges in a portion of each plot. Rice yielded
better in the puddled furrows (Table 21). The
higher yield with vegetables is a result of higher
nitrogen levels in these treatments. Considerably
more water was required to maintain standing
water in the puddled treatments as compared
with maintaining the upland area at close to
field capacity by flushing with water every 3 to
4 days. At higher nitrogen levels, however,

Tuber yield (t/ha)
36 I

0 60 70 80 90 100 110 120
Days after transplanting

11. Growth
varieties.

rates for the two best yielding sweet potato

MULTIPLE CROPPING 27

Plant ht
(cm)
200
65
59
110
63
80
70
60
62
51
63
59
60
136
54
52
555

Days to
maturity'
75
71
68
66
65
69
71
69
76
66
72
70
72
71
71
69
71

Erect or
creeperd
SC
E
E
E
E
E
E
E
E
E
E
E
E
SC
E
E
E

---

---

Table 21. The effect of seedbed preparation and seeding method on rice yield and water-use efficiency. IRRI, 1972-
73 wet and dry seasons.
Total Water-use efficiency
Planting method Rice yield (t/ha) at(mm/kg of rice)
water use
Alone With vegetables (mm) Rice alone Rice + vegetables
Puddled furrows, rice broadcast 4.66 6.51 1890 0.41 0.29
Puddled furrows, 3 rows rice 3.94 5.56 1890 .48 .34
Puddled furrows, 4 rows rice 4.04 5.50 1890 .47 .34
Upland ridge and furrow 3 rows rice 2.78 3.31 1020 .37 .31

water-use efficiency was greatest in the puddled
treatments. On heavy, low-lying, poorly drained
soil, management difficulties and high risk pre-
clude the use of complex management systems.
The more simple and straightforward the method
the greater the long-term payoff.
Relay cropping after rice. In intensive cultiva-
tion systems in Taiwan, relay planting of upland

Yield (t/ho, log scale)
7.0 -

0 7 14 21
Number of days overlap
12. Quadratic relationships between yields of different crops
and number of days of overlap with rice. IRRI, 1972 wet
season.

crops with rice at the end of the rice-growing
season is common. We tested crops relayed into
IR8 rice at different times before harvest to com-
pare their relative tolerance to shading during
early growth stages. Mung bean had little toler-
ance to shading past the first week (fig. 12). Soy-
beans and cowpea showed more gradual
reduction in yield with increasing time of overlap.
Corn was especially sensitive to shading but
sorghum was relatively tolerant for 14 days.
Sweet potato showed little effect of overlapping.
Rice yields were not affected. The rice canopy
was completely closed over the narrow ridges
(of the ridge-and-furrow system). This together
with the low light intensities of the late rainy
season heightened the competitive effect of over-
lap on the crops that followed rice.
Effect of puddling on crops after rice. To test
the Taiwan method of building "Poa" ridges in
puddled rice for following crops, we compared
this method following puddled rice with crops
grown on nonpuddled soil following upland
rice. The building of ridges in puddled soil before
rice harvest required 450 to 512 man-hours/ha
depending on the method used. These ridges had
to be cultivated after the rice was harvested. The
nonpuddled plots required 13 h/ha of hand-
tractor use to prepare the seedbed. It was
fortunate that a dry period in early October
permitted this land preparation. Yields of corn,
sorghum, soybeans, and mung were not statisti-
cally different between puddled and nonpuddled
soils (Table 22).

AGRONOMIC AND ECONOMIC FACTORS
Crop residue problems. To reduce the cash outlay
for nitrogen in intensive cropping systems as
well as to conserve a commodity which will
become increasingly scarce and more costly in

28 IRRI ANNUAL REPORT FOR 1973

the future, we are attempting to use grain legumes
more frequently.
One problem we encounter with grain legumes
is that yields drop when they are grown more
frequently than once a year. When cowpeas were
used, soil-borne disease built up rapidly, but this
did not seem to happen with mung and soybean.
Nematode build-up was likewise ruled out. To
study the effect, we planted mung, cowpea, and
corn for one season in a split-plot design. Then
after harvest the same three crops were planted
again in each of the plots at three levels of nitro-
gen. The yields of mung and cowpea were much
lower after mung or cowpea than after corn
(fig. 13). Corn yields were not affected by the
previous crop. There was no significant inter-
action between the effect of previous crop and
nitrogen level, indicating that the difference was
not due to nitrogen. Otherwise, corn would have
shown an even greater differential than did the
legumes, since it is generally more nitrogen re-
sponsive. Rice grown in the third season after
these combinations showed no effect at all from
previous crop combinations. The effect seems
especially prevalent on heavy soil that has
moderately poor drainage. Corrective studies
indicate that the response may be different de-
pending on the crops causing the effect. Mung
following certain combinations of crops re-
sponds to ferrous sulfate in addition to complete
fertilizer. There seem to be no interactions in
sensitivity between mung varieties and the
residual effect.

Sweet corn ears (t/ha)
12 1 -0

Mung yield ( kg/ho)

Table 22. Yield of crops following rice on puddled and
unpuddled soil. IRRI, 1972 wet season.

Yield (t/ha)
Nitrogen appliedYield (t/ha)
(kg/ha) Corn Sorghum Green soybeans Mung
Puddled
60 2.6 2.8 4.8 0.6
100 2.4 3.5 5.7 .4
150 3.0 3.1 5.5 .5
Unpuddled
60 2.6 3.1 4.2 .5
100 2.2 2.7 4.1 .5
150 3.2 3.1 4.8 .7

Weed management. On experiment stations,
standard cropping with high levels of chemicals,
intensive tillage, and relatively low leaf area
indices nearly always results in a shift of weed
species to predominantly grasses and sedges.
With high rainfall during the monsoon on a
heavy soil these species are extremely difficult to
control. In farmer's fields, where field crops make
full use of the seasonal moisture supply, this type
of weed climax is seldom found, even if several
crops a year are grown in intensive patterns.
Instead weed communities are composed of a
very few species, usually broadleaved weeds. In
many areas traditional cropping patterns appar-
ently have this built-in weed balance. Our goal
is to learn how to manage this shift while giving
economic control in each crop.
In a continuing year-round experiment at
IRRI, we have imposed four levels of weed
management on two cropping patterns. We have

Cowpea yield (t/ha)

S 6

4

2

25
Nitrogen applied (ka/ha)

0 -25 5
0 25 50

13. Yield of sweet corn, mung, and cowpea as influenced by nitrogen level and preceding crop. IRRI, 1973 dry season.

MULTIPLE CROPPING 29

Table 23. The effect of density of leaf canopy on indi-
vidual weed species. IRRI, 1973.

Weeds under low
density crop
Weed species canopy (no./sq m) Ratio*
1st 2nd 1st 2nd
season season season season
Digitaria sanguinalis 1325 79 0.80 0.40
Echinochloa colonum 181 48 0.60 .69
Eleusine indica 39 40 1.22 .69
Portulaca oleracea 126 153 1.06 .65
Amaranthus viridis 17 23 0.19 .29
Cyperus rotundus 59 138 0.93 .22
'Of weeds at high crop density compared with weeds at low
crop density.

high and medium levels of management using
chemicals and mechanical tillage under crop
patterns of high and low leaf area index. The
combination of control method and leaf area
index after two seasons has already caused a
marked shift in weed species (Table 23). Several
shade-sensitive grass species and sedges, especi-
ally Cyperus rotundus, have decreased markedly
under the high leaf area index. It may be possible
to shift the year-round, seasonally changing
weed pattern toward species which are more
easily controlled during the early growth stages
of each crop. In patterns where the soil is pud-

Dry weed wt (g/sq m)

dled for one crop or even flooded for several
weeks during the rice season, the effect on the
weed community and on subsequent control
requirements is dramatic.
To learn how to manipulate the shift of weeds
under different cultural practices we are study-
ing several species which are predominant in
fields having "experiment station" technology
and also some from farmer's fields. Weeds vary
in response to population and to shading. Portu-
laca oleracea shows little increase in dry weight as
plant population increases above a low level but
its response to nitrogen is nearly linear up to
150 kg/ha (fig. 14). It is quite sensitive to shade
(fig. 15). That helps explain why it becomes pre-
dominant in intensive systems under high
fertility and low leaf area index, for example,
where vegetables are grown intensively. Cyperus
iria has a much greater population response but
it responds to nitrogen only up to 75 kg/ha in the
wet season. Ipomoea triloba shows a shade-
tolerance pattern. Shade may have an even
greater effect through reduction of seed yield and
subsequently on population shift than through
reduction of dry matter.
Management of arthropods in crop litter. In
intensive cropping patterns, the handling of crop
stubble becomes a problem, especially where

Reduction in dry wt (%)

0 75 150 0 20 40 60 80 t10
Nitrogen level Shode (%)
14. Response of two weed species to nitrogen at high and 15. The response of two weed species to increasing shade
low plant densities. IRRI, 1973 wet season, level. IRRI, 1973 wet season.

30 IRRI ANNUAL REPORT FOR 1973

power is limited. Burning is seldom used in
intensive systems except in lowland rice. One
reason is that during wet weather the intensive
schedule does not permit drying. Another is that
following burning, nutrient loss by leaching is
much higher. It appears that on small farms
cutting the crop and allowing the stubble to
decay between the rows of the succeeding crop
will continue to be a common practice.
In intensively cultivated soils, organic litter
turn-over rate decreases, which may affect
natural buffering capacities of soils and bene-
ficial biotic relationships in cultivated fields. For
this reason the role of arthropods in hastening
organic decay is important.
A survey of arthropods associated with de-
composingcorn, mung, and peanut litterrevealed
that stratiomyid flies, oribatid mites, and col-
lembolans are the dominant agents of litter
breakdown. Careful counts revealed representa-
tives of 11 orders of macroarthropods and two
orders of microarthropods. There were four sub-
orders of Acarina represented by 27 genera. Pre-
datory arthropods like spiders, dermapterans,
and macrochelid mites were also abundant. As
expected, the population of these arthropods
varied with the type of litter; they also responded
differently to a treatment of the litter with
molasses as a food energy source (1 : 3 mixture
of molasses and water) which was applied as a
drench to boost initial microbial activity. Stra-
tiomyid larvae, for instance, increased more
rapidly on peanut litter than on corn.
Nitrogen utilization. Some intercrop combina-
tions like corn-rice not only have a higher total
productivity but also make more efficient use of
nitrogen. In the corn-rice trial, the total nitrogen
uptake was considerably higher with intercrop-
ping (Table 24). This cannot be explained solely
by greater total light interception, since the
combination did not have a much higher level
than rice alone except during the early weeks of
growth. Probably, light interception was not
only slightly higher but also more efficient. The
rice crop in the trial was affected by an early
infection of blast at nitrogen levels above 60
kg/ha. Fungicidal sprays kept incidence low
enough to give later recovery at higher nitrogen
levels. The incidence of blast was greater with
corn interplanting, so the response may have

Table 24. Total nitrogen content of above-ground plant
parts in corn-rice intercropping at maturity. IRRI, 1973
wet season.

Corn
Rice
Corn + rice

Corn
Rice
Corn + rice

Corn
Rice
Corn + rice

Corn
Rice
Corn + rice

Nitrogen content (kg/ha)
Corn Rice Corn + rice
60 kg/ha N
104 -
- 95 -
52 61 113
120 kg/ha N
81 -
62 -
58 54 112
180 kg/ha N
95 -
68 -
85 56 141
240 kg/ha N

been biased in favor ofmonoculture. The greater
efficiency of uptake in the intercrop was reflected
in a higher gross return (Table 5).
Power source interactions. The farmer's power
source plays a critical role in intensive systems.
In a replicated trial with large plots, six crops
were grown under irrigation during a 1-year
period. Rice was started in June and relay
planted with sweet potato. This was followed in
February with corn interplanted with cowpea
and in May by corn interplanted with mung. We
compared three power sources-hand labor,
hand labor plus carabao, and hand labor plus
hand tractor.
The three sources showed little difference in
total costs and returns (Table 25). Since the
methods were about the same in net return, the
choice of power source can be made on other
criteria. The cash flow of the systems, assuming
that a farmer hired the labor, carabao, and trac-
tor, was slightly in favor of hand labor. Less
money would be required to pay for the early
land preparation and thus a smaller cash outlay
would be required early in the season. Return on
labor was of course greater with the machines
than with carabao or hand labor (Table 26).
Return per unit of cash expense was higher with
hand labor than with other methods (Table 27).
Different power sources thus fit different re-
source patterns.

MULTIPLE CROPPING 31

Table 25. Costs and returns from three power sources in a cropping pattern of rice, sweet potato, cowpea and corn,
and mung and corn. IRRI, 1972-73.

Hand labor' Hand labor + carabaob Hand labor + hand tractors
Crop Total Variable Total Variable Total Variable
return costs Difference return costs Difference return costs Difference
(P/ha) (P/ha) (P/ha) (P/ha) (P/ha) (P/ha) (P/ha) (P/ha) (P/ha)
Rice 1000 1000 0 1100 900 200 1100 900 200
Sweet potato 4700 1200 3500 4700 1000 3700 4100 900 3200
Cowpea and corn 3100 1600 1500 3000 1300 1700 2700 1100 1600
Mung and corn 3800 1800 2000 3800 2200 1600 4300 2300 2000
Net return for pattern 7000 7200 7000

8At P0.75/h. bAt P1.75/h. cAt P7.50/h.

Consideration of timing of operations, how-
ever, gives a quite different picture. If a farmer
has 1 hectare of land and three man-units of
labor in addition to one carabao or one hand
tractor, the advantage weighs heavily in favor
of the mechanized operation. With one tractor
the cropping pattern would have been roughly as
accomplished at IRRI with the land being
unplanted 7 percent of the time. With a carabao
and three men, 1 additional month would have
been required, with the land idle 16 percent of
the time. With hand labor only, 2 more months
would have been required, with the land idle
22 percent of the time. If weather conditions
were not favorable for field operations all of the
time, the hand labor system would take still
longer since field preparation could not be car-
ried out during the expected brief periods when
weather conditions were favorable. With hand
labor only, and a limitation on labor, two crops
per year is a more reasonable pattern.
The total energy balance of the three methods
is surprisingly similar (Table 28). Hand labor
has a slight advantage in efficiency over other
power sources but not as great as some reports
indicate. The energy equivalent of the cash
input was, surprisingly, three times higher than

Table 26. Return over variable cost per hour of labor.

Return (P.ha-'-h)
Crop Hand labor Hand labor +
Hand labor + carabao hand tractor
Rice 0.80 1.20 1.70
Sweet potato 4.30 6.40 9.00
Cowpea and corn 2.10 3.30 4.40
Mung and corn 1.70 1.50 2.20
Total pattern 2.20 2.60 3.70

that of labor and power inputs, indicating an
unrealistically high proportion of energy, for
Southeast Asia, from modern chemical inputs.
These relationships have important implications
on a national scale.
Economic comparisons of modern intensive
production. In evaluating economic returns from
cropping patterns it is best to take data from
farmers' fields which are in routine production.
With new patterns, however, the farmer must be
induced to grow them or the researcher must do
it himself. We are currently using both methods,
with the more complex irrigated patterns being
tested at IRRI.
The managed plots at IRRI are set up in four
replications. The first replication is 25 x 25 m
and is used for yield and for labor-use studies.
The remaining three replications are 7 x 25 m.
The 25-m-row length permits hand tractor or
carabao operations so that management simu-
lates that of a farmer's field. During 1972-73,
five 1-year patterns were set up to compare
productivity and returns (fig. 16). The level of
management was patterned after what a good
farmer might use. The patterns included com-
binations of rice and legumes; rice, legumes, and

Table 27. Return over variable cost per peso of cash
expense.

Return (P/P cash expense)
Crop Hand labor Hand labor +
Hand labor + carabao hand tractor
Rice 0.00 0.30 0.30
Sweet potato 7.50 5.10 5.10
Cowpea and corn 2.00 1.90 2.00
Mung and corn 7.50 1.50 1.50
Total pattern 3.50 2.80 2.00

32 IRRI ANNUAL REPORT FOR 1973

vegetables; and rice, a root crop, and a feedgrain.
Cash and labor inputs were expected to vary
widely between patterns.
Yields and returns were affected not only by
the season and amount of rainfall, but also by
the market price at the time of harvest (Table 29).
Labor requirements and returns varied from 36
man-hours at P3/man-day to 275 man-hours at
P25/man-day. Rice yields and returns were low
because of a severe outbreak of grassy stunt
virus. The highest return was P104/man-day on
112 hours for corn-sweet potato. With many
legume crops like mung, the cash return and
protein production were considerably higher
when intercropped. Otherwise mung is profitable
only with little management. The soybeans were
low yielding presumably due to the residual
effect of the preceding cowpea crop. Normal
protein production of green soybeans should be

PATTERN I
RICE COWPEA SWEETPOTATO CORN

PATTERN 2
RICE
SWEETPOTATO 7OKRN
PATTERN 3
7RICE I COWPEA I SYBEAN!I MUNG

PATTERN 4
S RICE US' MUN ITOMTO
TOMATO OKRA
PATTERN 5
RICE I TOMATO MUNG TOMATO

J A S 0 N J F M A M J J A

16. Crop sequence and timing of five irrigated cropping
patterns.

Table 28. Relative energy balance for three power sources in an intensive year-round cropping pattern.a

Energy balance (Mcal/ha)
Power Power Other variable Total energy Marketable energy
source inputs used
source inputs used Total Per Mcal used
Hand labor 845 6,035 6,880 56,395 8.20
Hand labor + carabao 2,783 6,035 8,815 55,089 6.25
Hand labor + hand tractor 2,012 6,035 8,047 50,290 6.25

'Assumed energy equivalents: Human labor-0.175 Mcal/h; animal power-2.4 Mcal/h; fuel-8.45 Mcal/liter; heat of combustion
of dry matter-3,700 Mcal/kg; value of goods and services-2.59 Mcal/ P.

Table 29. Yield and returns for individual crops in irrigated rotations.

Marketable digestible
Crop Yield Labor Return above variable Marketabe
Crop Yield Labor
ha) (man-d ) cost (P/ha) Protein Nutrients
(t/ha) (man-day/ha) (gh
Total Per man-day Total Per day (kg/ha)
Tomato 24 133 3,320 25 67 0.8 70
Tomato and 20
Tomato and 20 275 6,880 25 138 1.6 140
bush sitao 0
Okra and 21
Okraand 21 271 5,420 20 407 4.1 1760
mung 0.5
Sweet potato 17 104 2,700 26 0 0 2080
Rice 2 36 110 3 126 1.0 1570
Corn 4 44 440 10 286 2.8 3150
Corn and 7
Corn and 7 112 11,670 104 224 1.9 9180
sweet potato 25
Corn and 5
orn and 5 64 1,540 24 96 1.4 1060
cowpea 0
Cowpea 2 61 1,590 26 366 5.2 1280
Mung 0.8 95 570 6 190 2.8 670
Soybean (green) 2 75 380 5 75 1.2 450

MULTIPLE CROPPING 33

Table 30. Labor requirements, productivity and returns from five irrigated cropping patterns.
Marketable digestible Return above variable cost (P)
Cropping Labor Total return
pattern (man-days/ha) Protein Nutrients (P/ha) Per Per hour Per peso cash
(kg/ha) (kg/ha) hectare of labor expense
1 355 710 13,135 21,105 15,340 6.16 4.22
2 164 410 6,970 6,190 3,380 3.34 1.85
3 215 860 4,085 6.615 2,180 2.02 0.69
4 542 542 4,336 19,475 10,905 2.75 2.44
5 388 388 3,104 18,490 11,625 4.50 2.56

4 to 5 kg ha-' day- Sweet potato, corn, and
the combination are extremely high in produc-
tion of total digestible nutrients.
Various measures of returns for the overall
cropping pattern showed similar trends (Table
30). Rice followed by legumes (pattern 3) gave
the lowest return on labor and cash expense as
well as lowest total nutrient production. Total
return and return on investment are not closely
related to nutrient production, especially when
high-return vegetables are included. If a vege-
table market were not available, and especially
if labor supply was limited, pattern 2 seems far
more attractive than the other patterns. If labor
is more plentiful, pattern 1 offers increased
employment with a high return.
It thus appears that protein and total nutrient
productivity can be made profitable, but not

with legumes alone. Careful mixtures of legumes,
grain crops, and root crops have exciting poten-
tial, not only for high levels of nutrient produc-
tion, but also for total productivity.
Using the resource-utilization approach, it
seems evident that for many farmers novel types
of technology may be quite relevant. It is also
clear that huge gaps exist in our knowledge of
cropping systems for the Asian rice farmer. The
effect of soil tillage properties on cropping pat-
tern potential has not been studied. To reach
our long-range goal of eventual modeling of
cropping systems, we must fill in several of these
gaps before our model can hope to be useful. For
the present, however, there seem to be several
ways in which simple changes can be made to
improve production efficiency for the Southeast
Asian rice farmer.

34 IRRI ANNUAL REPORT FOR 1973

Statistics We evaluated an experimental
approach to the identification
and quantification of yield constraints in farmers' fields. Instead of
simply characterizing the farmers' practices, as is done in conventional
farm surveys, the new approach uses field plot technique to assess, at
each sample farm, the possible yield increase due to improved manage-
ment. We used a factorial combination of several cultural practices
each at two levels: the farmer's level and the recommended level. E
While both genetic and non-genetic variances of protein content are
smaller than those of grain yield, the ratio of these variance compon-
ents is much more favorable for grain yield than for protein. More-
over, the negative association between grain yield and protein content
is primarily due to the environment rather than to the genotype. These
results seem to indicate that the major difficulty in improving protein
content of rice is not the negative correlation with grain yield nor the
interference of large environmental variance, but rather the small
genetic variance for protein. l The yield response of rice to nitrogen
fertilization was found to be adequately described by quadratic res-
ponse functions in 1,047 out of 1,304 response curves examined.

FACTORS LIMITING FARMERS' YIELDS
Despite the rapid adoption of the improved rice
varieties, farmers achieve only a small fraction
of the varieties' yield potential. The usual way to
study the causes of low farm productivity is a
survey in which information on yield and cultural
practices are obtained from sample farms,
usually through interviews. But yield variation
among farms can not be totally explained by
cultural practices alone-climatic and soil differ-
ences are at least as important. To remedy this,
some studies include the monitoring of the
physical environment throughout the growing
season. The major disadvantages of that ap-
proach are that monitoring climatic conditions
is laborious and time consuming, and that data
on physical environment can be highly useful
only if its relation to yield and other cultural
practices is known beforehand.
Since the limiting factors that are of major
interest to rice researchers and farmers are those
that are within human control-management
and cultural practices-we have evaluated a
procedure for removing the complications eman-
ating from large climatic and soil differences
from one sample farm to another. The procedure
consists of obtaining sample farms as is norm-
ally done in surveys and conducting field plot
experiments on the farms to obtain information
from actual measurements instead of from the
farmer.
A factorial experiment involving (i) insect
control, (ii) water management, (iii) weed
control, (iv) fertilizer, and (v) seed source and

seedling management, each at two levels, was
conducted at several farms in the 1972 dry and
wet seasons. In the 1973 wet season, only four
factors were tested (water management was
excluded). The sample farms were purposely
selected based upon reported yield levels. The
two levels of each factor tested were (i) the
farmer's practice, that which the farmer of the
sample farm actually used (thus it varied from
one sample farm to another), and (ii) the "im-
proved" practice, the standard practice used in
IRRI field experiments. The improved practice
consists of 120 kg/ha N in the dry season and
90 kg/ha N in the wet season, 3 to 5 cm of stand-
ing water maintained up to 2 weeks before
harvest, as close to weed-free condition as
possible, maximum protection against insects
and diseases through application of insecticides,
and use of dapog seedlings, 10 to 13 days old,
grown from breeder's seed from IRRI or from
the University of the Philippines at Los Baiios.
Aside from yield, data on weeds, off-type
plants, rat damage, and insect and disease
incidence were collected. A complete record of
all management and cultural inputs from seed-
ling preparation to harvest was kept for both the
farmer's practices and the improved practices.
Relative contribution of inputs to yield increase.
In the dry season, improved practices greatly
increased yields in farmers' fields compared with
farmers' practices (Table 1). On one farm im-
proved practices gave a yield of 9.6 t/ha. The
absolute yield increase ranged from 2.4 t/ha to
4.4 t/ha (about 50 to 300%). Each input gave
some yield increase but insect control, fertilizer,

Table 1. Contribution of five management inputs toward improving rice yields in farmers' fields. Laguna, Philippines,
1972.

Grain yield (t/ha) Contribution (t/ha)
Farm Variety
no. planted Farmer's Recommended Difference Insect Water Nitrogen Weed Seedling
inputs inputs control management fertilization control management
Dry season
1 C4-63G 3.7 7.4 3.7 0.8 1.3 0.9 0.5 0.2
2 C4-63G 3.8 6.2 2.4 0.9 1.0 0.2 0.0 0.3
3 C4-63G 1.4 5.8 4.4 1.9 1.3 0.9 0.1 0.2
4 IR8 6.6 9.6 3.0 1.1 0.1 0.8 0.4 0.6
Avg 3.9 7.3 3.4 1.2 0.9 0.7 0.3 0.3
Wet season
1 IR22 4.3 4.8 0.5 0.7 -0.1 -0.1 0.2 -0.2
2 C4-137 4.6 5.2 0.6 0.0 0.1 0.0 0.5 0.0
3 IR579-48-1 4.2 5.0 0.8 1.5 -0.3 -0.2 0.3 -0.5
Avg 4.4 5.0 0.6 0.7 -0.1 -0.1 0.3 -0.2

36 IRRI ANNUAL REPORT FOR 1973

Table 2. Contribution of four management inputs toward the improvement of rice yields in farmers' fields. Laguna,
Philippines. 1973 wet season.

Farm Variety Grain yield (t/ha) Contribution (t/ha)
Farm Variety
no. planted Farmer's Recommended Difference Insect Nitrogen Weed Seedling
inputs inputs control fertilization control management
1 IR20 3.4 6.0 2.6 2.0 0.1 0.3 0.2
2 IR20 5.0 6.5 1.5 1.1 0.0 0.0 0.4
3 IR20 1.5 3.3 1.8 1.3 0.1 '0.4 a
4 IR22 4.1 5.9 1.8 1.3 0.2 0.0 0.3
5 IR22 1.9 4.5 2.6 2.0 0.2 0.4 0.0
6 IR1561-228-3 4.5 6.0 1.5 1.1 0.0 0.3 0.1
7 IR1561-228-3 3.4 4.8 1.4 0.9 0.3 0.1 0.1
8 C4-63G 1.7 4.8 3.1 1.6 0.6 0.4 0.5
9 C4-63G 2.2 3.9 1.7 1.1 0.0 0.4 0.2
10 C4-63G 2.3 4.2 1.9 1.8 -0.5 0.6 0.0
11 C4-63G 3.3 4.1 0.8 0.5 -0.2 0.5 0.0
12 C4-63G 2.2 4.3 2.1 1.3 0.1 0.7
Avg 3.0 4.9 1.9 1.3 0.1 0.3 0.2
aData not available.

and water management, were the most crucial
in raising rice yields in these farms. They contrib-
uted an average of 83 percent to the total yield
increase. Their effects, not unexpectedly, varied
greatly from farm to farm, since the level of
farmers' management varied greatly among
farms.
In the wet season, the level of yield increase
due to improved practices was generally low,
averaging only 0.6 t/ha or 14 percent. Of the five
factors tested, insect control and weed control
caused the entire yield increase, although the
increase was not large. As expected, water
management was not as big a problem in the
wet season as in the dry season. Moreover, while
in the dry season, some improvement in the
farmers' nitrogen fertilization practices (avg: 87
kg/ha N) was possible, it was not so in the wet
season (when farmers used an average of 65
kg/ha N).
The 1973 wet season trial confirmed these
results (Table 2). Again, insect control ranked
as the most crucial factor in improving rice
yields in the farms, giving an average yield
increase of 1.3 t/ha, which is 68 percent of the
total yield increase. Weed control was the second
most important factor with an average yield
increase of only 0.3 t/ha.
The greatest yield constraint in farmers' fields
in the study area seems to be control of pests and
diseases. When pest and disease problems were

minimized, yields on these farms were raised
1 t/ha, irrespective of season. In the dry season,
improvement in water management could raise
yields 0.9 t/ha and the use of higher nitrogen
rates could raise yields 0.7 t/ha. Improvement in
weed control management as well as in seed
source and seedling management compared with
the farmers' practices did not seem to give
appreciable effects.
Evaluation of techniques. An important aspect
of the proposed procedure is the experimental
design or the choice of treatments to be tested.
If interactions among the various inputs exam-
ined are appreciable, then factorial treatments,
whether complete or incomplete, may be more
desirable than the discrete management pack-
ages. The use of complete factorial treatments,
of course, may enlarge the size of the experiment
which is undesirable, especially for trials in
farmers' fields. During 1973 wet season we
experimentally evaluated some of the possible
interactions among the management inputs with
the average farmers' level as control. We found
that weed-control level gave a large differential
effect on the nitrogen response of rice (fig. 1),
indicating that an optimum nitrogen rate derived
from fertilizer trials conducted at experiment
stations under high management levels may not
necessarily be appropriate under farm conditions
having lower levels of other management inputs.
Virus incidence (grassy stunt) was observed to

STATISTICS 37

0 30 60 90 120
Nitrogen applied (kg/h )
1. Nitrogen response of rice (IR20 and IR1561-228-3) grown
under intermittent irrigation, as affected by weed control
levels. IRRI, 1973 wet season.

be higher under continual flood irrigation condi-
tion than with intermittent irrigation, and slightly
higher in weeded plots than in nonweeded plots
(Table 3). These results seem to indicate a great
dependence of the benefit of one input on the
levels of other inputs, and the danger of extra-
polating results obtained under experimental
conditions to farmers' fields where the level of
input use is generally lower. Because of the
apparent importance of interaction effects,
factorial treatments should be used in this type
of experiment.
The validity of the proposed approach de-
pends greatly on the success of the simulation of
farmer's practices, which can be measured by

the agreement between grain yield of farmer's
paddy and that from experimental plots receiv-
ing the farmer's level in all the factors tested.
Results of 1973 wet season indicated no bias in
the simulation technique (Table 4). In most
farms, the agreement was good; only three farms
had large differences (0.8 to 1.0 t/ha). Of the four
factors tested in the 1973 wet season trial,
insecticide application was the most difficult to
simulate. Application made 1 or 2 days later than
the farmer could make a great difference since
the effectiveness of insecticides depends on
weather conditions, particularly rainfall.
Placing plots with low insect control level
(farmer's practice) adjacent to those with high
insect control level (improved practice) tended
to give a slight overestimation in yield (Table 5).
Moreover, because of the difficulties encountered
in simulating farmer's insecticide practices it may
be more practical to have the insecticides applied
by the farmer himself even on the experimental
plots. These findings suggest that the two sets of
plots according to the insect control level should
be separated to avoid a possible bias in yield as
well as to facilitate the farmer's insect-control
operation.
For conducting this type of experiments in
farmers' fields, a plot size that gives a net harvest
area (after exclusion of border rows) of 6 to 8
sq m per plot seemed sufficient (fig. 2).
In two seasons of tests in 1972, the experi-
mental procedure was not satisfactory for
assessing the contribution of water management
to farmers' yields. We had great difficulty in
maintaining the desired water level for
"improved" plots because water was not avail-

Table 3. Degree of virus* incidence on IR1561-228-3 and IR20 as affected by water management and weed control
levels, at varying nitrogen levels. IRRI, 1973 wet season (Data are averages of four replications).

Weed control Water Virus incidence (%)
Weed control Water
level management 0 kg/ha N 30 kg/ha N 60 kg/ha N 90 kg/ha N 120 kg/ha N Avgb
IR1561-228-3
Non-weeded Continuous flooding 3.9 2.7 5.2 4.8 5.7 4.5 c
Intermittent irrigation 0.6 0.8 0.8 1.0 0.6 0.8 d
Weeded Continuous flooding 8.1 8.6 6.4 5.1 6.6 7.0 b
Intermittent irrigation 1.8 1.4 2.0 1.2 0.7 1.4 d
IR20
Non-weeded Continuous flooding 13.0 4.4 7.1 7.4 7.4 7.9 b
Weeded Continuous flooding 17.0 22.6 11.2 18.0 14.8 16.7 a
Intermittent irrigation 6.6 4.8 5.9 7.2 4.5 5.8 bc

aMostly grassy stunt. bMeans followed by a common letter are not significantly different.

38 IRRI ANNUAL REPORT FOR 1973

able at all times. Other procedures should be
evaluated, such as sampling from farms that
have been stratified into various categories of
water availability.

VARIABILITY IN PROTEIN CONTENT OF
RICE
Two problems widely believed to hinder the
improvement of grain protein in rice are that
protein content is highly influenced by environ-
mental factors, and that protein content and
grain yield seem to be negatively correlated. We
examined the effects of environment on protein
content of rice, attempted to identify the test
condition that minimizes experimental error in
protein trials, and investigated relationships
between protein content and grain yield.
Phenotypic variance within varieties. Experi-
mental data on protein content and grain yield
of IR8 and IR480-5-9 from experiments conduc-
ted by the agronomy and varietal improvement
departments were analyzed. We found that the
variability due to environment constituted a
substantial portion of the total variability in both
protein content and grain yield. In 964 experi-
mental plots of IR8, brown rice protein ranged
from 4.8 to 12.1 percent, grain yield from 1.0 to
9.8 t/ha, and protein yield from 69 to 686 kg/ha
(fig. 3). Protein content varied greatly among
locations (Table 6) and among cropping seasons
(Table 7). In addition to plant density, nitrogen
fertilization, and method of nitrogen application
previously shown by IRRI agronomists to affect

Table 4. Grain yields obtained in farmer's paddy and
from simulation of farmer's practices in experimental
plots, under varying farm conditions. Laguna, Philip-
pines, 1973 wet season.

Variy Yield (t/ha)
Variety
planted Simulated Farmer's
farmer's plots paddy Difference
IR20 5.0 4.2 0.8
IR20 1.5 1.3 0.2
IR22 4.1 3.9 0.2
IR22 1.9 1.7 0.2
IR1561-228-3 4.5 5.5 -1.0
IR1561-228-3 3.4 3.5 -0.1
C4-63G 1.7 1.2 0.5
C4-63G 2.2 2.4 -0.2
C4-63G 2.3 3.1 -0.8
C4-63G 2.2 1.8 0.4
Avg 2.9 2.9 0.0

Experimental error (g/sq m )2

1200

= 5230X-'l29
800 (R2 0.993**)

400

0 I-- I
S ill I I
0 3 6 9 12
Harvest area per plot (sq m)
2. Relation between experimental error and net plot size for
rice experiments in farmers' fields. Bay, Laguna, 1972 dry
season.

grain yield and protein content, we found that
improved water management and weed control
increased both (Tables 8 and 9) too. On the other
hand, improved pest and disease control in-
creased grain yield without affecting significantly
protein content (Table 10).

Table 5. Yields of plots in farmers' fields receiving low
levels of insect control adjacent to or separated from
plots receiving maximum insect control. Laguna,
Philippines, 1973 wet season.

V y Grain yield (t/ha)
Variety
planted Adjacent Separated Difference
IR20 5.3 4.9 0.4
IR20 2.2 1.5 0.7
IR22 4.9 4.1 0.8
IR22 2.2 2.1 0.1
IR22 2.5 2.2 0.3
C4-63G 2.9 1.7 1.2
C4-63G 2.0 2.1 -0.1
C4-63G 2.9 2.7 0.2
C4-63G 3.0 3.3 -0.3'
C4-63G 2.7 2.2 0.5
Avg 3.1 2.7 0.4

STATISTICS 39

Experimental plots (no)
2001

II

=X82%
cv= 13 %

100 H

& Ii,

X=56t/ho
c=28%
,, ill,/

I --EEE I I m mmmm EmmW E I 1 nEEMMEMEMEME I
59 69 79 89 99 109 119 09 21 33 46 58 70 82 94 124 268 412 556 700 844
Brown rice protein (%) Groin yield (t/ho) Protein yield (kg/ha)
3. Frequency distribution of brown rice protein content, grain yield, and protein yield of IR8 samples from 964 experimental
plots in 31 trials. IRRI, 1968-1972.

The experimental error of protein content not
only was generally lower than that of grain yield
(Table 11), its magnitude was also less influenced
by the cultural practices employed. While the
experimental error of grain yield was greatly
reduced with nitrogen fertilization (Table 12),
that of protein content was not appreciably
affected. On the other hand, method of nitrogen

Table 6. Brown rice protein and grain yield of IR8
(unfertilized) grown in agronomytrials at four locations
in the Philippines. 1969 wet season (Data are averages
of three replications).
Location Protein (%) Yield (t/ha)
IRRI 7.5 + 0.2 4.7 0.1
Bicol 7.1 0.3 4.6 0.5
Maligaya 6.7 + 0.1 5.2 + 0.1
Visayas 5.5 + 0.4 4.0 + 0.2

Table 7. Brown rice protein and grain yield of six rice
varieties as affected by crop season. IRRI. 1971-1972
(Data are averages over two trials each with three
replications).
Dry season Wet season
Variety Protein Yield Protein Yield
(%) (t/ha) (%) (t/ha)
IR8 7.1 5.02 7.8 3.62
IR22 7.6 4.03 8.6 3.52
IR24 7.4 4.67 9.0 4.00
IR20 7.6 4.69 9.1 3.64
C4-63G 7.4 4.70 8.8 3.49
RD-3 7.8 4.05 8.8 3.37
Avg 7.5 4.53 8.7 3.61

application significantly influenced experimental
errors of both grain yield and protein content
with the lowest errors obtained when nitrogen
was applied in split dose-basal and at panicle
initiation (Table 13). Thus the test condition
that minimizes experimental error for grain yield
is also appropriate for protein.
Data from 964 experimental plots of IR8 and
538 plots of IR480-5-9 grown under varying
environmental conditions at IRRI farm revealed
quadratic relationships between grain yield and
percentage protein content (fig. 4). Grain yield
and protein content increased simultaneously
only up to a point beyond which an increase in
protein content resulted in a decrease in grain
yield. This suggests that there is a protein
threshold representing each variety's grain pro-
tein potential. For IR8, this protein threshold
was estimated at about 8.5 percent, with a
corresponding average grain yield of 6.6 t/ha in
the dry season and 5.1 t/ha in the wet season.
For IR480-5-9, a promising high-protein line,
the protein threshold was about 10.3 percent
with average grain yield of 6.5 t/ha for the dry
season and 4.3 t/ha for the wet season.
Phenotypic variance among varieties. A series
of experiments were conducted in cooperation
with the agronomy and chemistry departments
at the IRRI farm for four consecutive seasons in
1971 and 1972 to examine the different com-
ponents of variance and covariance in both
protein content and grain yield. In each experi-

40 IRRI ANNUAL REPORT FOR 1973

Table 8. Brown rice protein and grain yield of C4-137 grown in a farmer's field under different nitrogen rates and
different levels of water management and weed control. Laguna, Philippines, 1973 dry season (Data are averages of
four replications).

Protein (%) Yield (t/ha)
Weed control
level 60 kg/ha N 120 kg/ha N Avga 60 kg/ha N 120 kg/ha N Avga
Intermittent irrigation
Low 6.7 7.5 7.1 a 4.4 5.5 5.0 a
High 6.9 7.7 7.3 b 5.5 6.2 5.8 b
Continuous flooding
Low 7.2 8.2 7.7 c 5.4 6.6 6.0 b
High 7.9 8.2 8.0 d 6.3 7.0 6.6 c

'Means followed by a common letter are not significantly different at the 5% level.

Table 9. Brown rice protein and grain yield (fertilized and unfertilized) as affected by water management and weed
control levels. IRRI, 1973 dry season (Data are averages of IR20 and IR22).
Protein (%) Yield (t/ha)
Weed control level
Unfertilized Fertilized' Avgb Unfertilized Fertilizeda Avgb
Intermittent irrigation
Non-weeded 7.2 7.5 7.4 c 2.89 4.25 3.98 c
Weeded 7.6 7.7 7.7 b 3.54 4.91 4.63 b
Continuous flooding
Non-weeded 7.6 8.0 7.9 b 3.66 4.86 4.62 b
Weeded 7.9 8.2 8.1 a 3.88 5.56 5.22 a

'Average of four levels of nitrogen, each with four replications. bMeans followed by a common letter are not significantly different at the
5% level.

ment, 16 varieties were tested under four test
conditions in three replications. Eleven varieties
were common throughout the four trials while
the rest varied from one trial to another. To
ensure a wide range of phenotypic variability,
the varieties were chosen primarily for their
large differences in both protein and grain yield.
Moreover, varying levels of nitrogen and plant
spacing, the major cultural practices affecting
both characters, were included. Protein content
ranged from 6.1 to 15.9 percent and grain yield
from 0.51 to 7.17 t/ha (Table 14).
This series of experiments confirmed previous
findings that environmental variance of grain
yield is larger than that of protein content (Table
15). It was clear, however, that the genetic vari-
ance of grain yield is also much larger than that
of protein. In fact, the difference between genetic
variances of grain yield and protein content was
more pronounced than that between environ-
mental variances. As a result, the ratio of genetic
to environmental variances was more favorable
for grain yield (1.0 : 2.8) than it was for protein
(1.0: 5.2). Thus, the difficulty in the improvement
of protein content of rice is not as much due to

the large environmental variance as it is to the
small genetic variability.
As expected, the total phenotypic covariance
between grain yield and protein content was
large and negative. The separation of this covari-
ance into its genetic and environmental com-
ponents (including genetic x environment inter-
action) indicated that all of the negative associa-
tion between grain yield and protein content was
due to the latter component-the genetic covari-
ance was small and positive. Except for nitrogen

Table 10. Brown rice protein and grain yield of three
rice varieties grown in farmers' fields under different
levels of pest and disease control. Laguna, Philippines,
1973 dry and wet seasons (Data are averages of 8 to 16
replications).

Protein (%) Yield (t/ha)
Variety Crop Low High Low High
season insect insect insect insect
control control control control
C4-137 Dry 7.6 7.4 5.5 6.2
IR20 Wet 8.3 8.2 4.8 6.0
IR1561-228-3 Wet 8.9 9.0 4.4 5.6
IR20 Wet 9.3 9.3 1.5 5.8
Avg 8.5 8.5 4.0 5.9

STATISTICS 41

Table 11. Experimental error of protein content and
grain yield estimated from seven series of rice field
experiments. IRRI, 1971-1972.

Coefficient of variation (%)
Protein Yield
Experiment Degrees of Protn
no. freedom Dry Wet Dry Wet
Year season season season season

1 1971 110 6.3 5.9 8.9 12.4
2 1971 130 5.4 5.9 7.7 9.1
3 1971 120 8.3 7.5 13.6 15.4
4 1972 110 6.6 5.7 8.5 9.4
5 1972 130 7.9 6.5 10.2 9.4
6 1972 120 5.4 7.7 11.6 14.9
7 1972 326 7.3 6.9 9.3 8.4
Combined 1046 6.9 6.6 9.8 10.7

Table 12. Experimental error' of grain yield and brown
rice protein estimated from agronomy trials, as affected
by the rate of nitrogen application. IRRI, 1971-1973.

Yield Protein
Nitrogen applied Yield Protein
(kg/ha) Mean (t/ha) cv (%) Mean (%) cv (%)
Dry season
0 4.54 14.7 7.8 7.4
60 5.77 10.8 8.4 5.7
90 6.35 10.0 8.8 7.5
120 6.63 8.7 9.2 6.2
150 6.55 8.3 9.5 7.4
Wet season
0 3.52 13.7 7.6 5.9
30 3.86 8.8 8.1 5.9
60 4.10 9.0 8.2 5.5
90 4.29 9.5 8.4 6.9
120 4.29 8.8 8.7 6.8

aData are averages over six trials for grain yield and four trials
for brown rice protein, each trial consisting of 14 varieties
tested with four replications.

Table 13. Experimental error (based on 90 degrees of
freedom) of grain yield and brown rice protein estim-
ated from agronomy trials, as affected by the time of
nitrogen applications. IRRI, 1969-1970.

Time of Yield Protein
Time of
application Mean (t/ha) cv (%) Mean (%) cv (%)
1969 wet season (60 kg/ha N)
Basal 4.37 14.0 9.4 9.0
Basal + panicle
initiation 4.54 10.7 9.5 6.5
Basal + heading 4.72 10.5 9.7 6.5
1970 dry season (150 kg/ha N)
Basal 6.00 8.6 8.6 7.1
Basal + panicle
initiation 6.24 6.9 9.0 6.5
Basal + heading 5.75 10.2 9.6 6.9

Groin yield (t/ho)
7 o 0
DRY SEASON
SN%
6 o0 %o

5- 0 0
/. ./\

4 y--21.66+672X-0.40X2 0 0
(R2= 0794**)
IR480
Y=-31 20+7.34X-036X2
(R2 0.748**)
2
I I I I

0 5 6 7 8 9 10 II 12 13 14
Brown rice protein (%)
4. Relations between protein content and mean grain yield
of IR8 (from 964 observations) and IR480-5-9 (from 538
observations), by crop seasons. IRRI.

fertilization, which increased both characters
simultaneously, all other environmental factors,
especially cropping seasons which favored grain
yield, depressed protein content and vice versa.
Because of the important implications of these
findings to the improvement of protein content
through breeding, it is necessary that these
results be confirmed in further studies with the
inclusion of more genotypes and environments.

YIELD RESPONSE TO NITROGEN

We examined nitrogen response curves taken
from 154 fertilizer trials conducted by the
agronomy department from 1966 to 1972,
involving different varieties and selections grown
under widely different management and environ-
mental conditions. In all trials, at least four
nitrogen levels were tested. We found that the

42 IRRI ANNUAL REPORT FOR 1973

yield response to nitrogen in rice is described
appropriately by the quadratic functions:
Y = a + bN + cN2, where Yis grain yield, N is
nitrogen rate, and a, b, c are the regression
parameters. In 1,047 of the 1,304 response curves
examined, quadratic response functions accoun-
ted for more than 80 percent of the yield vari-
ability. The curves that had coefficients of
determination (R2 values) from quadratic fits
of less than 80 percent came mostly from trials
which involved traditional varieties or which
were made in the wet season. For improved
varieties or selections grown in the dry season
quadratic functions can be expected to give
satisfactory fits about 90 percent of the time;
under other conditions, satisfactory fits can be
expected in only 65 to 75 percent of the time.
Several types of nitrogen response curves were
observed (fig. 5): A) Grain yield increased with
nitrogen level, although the yield increment
became less and less as higher nitrogen rates were
used, and finally reached a point where further
increase in nitrogen brought about a reduction
in yield. This type of curve, which was the most
common, is necessary for estimating economic-
ally optimum nitrogen rates. B) The response
was still in the linear phase, that is, grain yield
increased at the same rate throughout the range
of nitrogen levels used. Optimum nitrogen rate
can not be derived from this type of curve since
maximum yield has not been reached. To avoid
getting type B curves, the maximum nitrogen
rate tested in the trial should be sufficiently high.
C) Yield was reduced as nitrogen rates increased.
This type of curve occurred mostly with tradi-
tional varieties grown in the wet season.
To find one or more measures for comparing
and describing a large number of nitrogen
responses, several parameters were examined.
Nmx (the nitrogen rate that maximizes yield),

Table 14. Range and mean of grain yield and brown rice
protein of 11 rice varieties and lines tested under
varying environments. IRRI, 1971 and 1972 dry and
wet seasons.

Designation Yield (t/ha) Protein (%)
Designation
Range' Mean Ranges Mean
IR8 2.56-6.73 4.41 7.0-11.1 8.5
IR22 3.13-6.46 4.27 7.6-10.6 9.0
IR24 3.20-6.73 4.56 7.1-10.7 8.6
IR20 2.53-7.17 4.39 7.6-11.5 9.1
C4-63G 1.88-5.76 3.89 7.4-12.6 8.9
BPI-76-1 1.84-5.25 3.41 7.8-15.9 10.3
RD-3 1.74-6.56 3.98 7.6-11.4 9.0
Intan 0.51-3.67 1.68 6.1-10.9 8.5
IR480-5-9 3.00-6.31 4.00 8.2-13.1 10.5
IR667-98-1 2.47-6.36 3.98 7.7-12.5 9.6
IR160-27-3 3.00-6.72 4.28 8.3-12.4 9.9

'Over 16 environments composed of four test conditions and
four cropping seasons, each replicated three times.

Ymax (the maximum yield), and Y, (increment
of yield increase based on Nmax rate) were
satisfactory. The use of these parameters in
distinguishing nitrogen responses in the dry and
wet seasons under various conditions is illus-
trated in figure 6. The dry season crops required
a higher nitrogen rate to attain the maximum
yield (Nmax of 112 kg/ha N for dry season and
75 kg/ha N for wet season), while the maximum
yield, as well as the returns in terms of kilograms
of grain per kilogram of nitrogen, was also
higher (Ymax of 6.6 t/ha in dry season and 4.8
t/ha in wet season; and Y, of 18.2 kg grain/kg N
in the dry season and 13.6 kg grain/kg N in the
wet season). This indicates clearly that yield
response to nitrogen application in the dry
season is better than in the wet season. Of the
various factors examined, the two major ones
affecting nitrogen response are crop season and
varietal type. The differences are illustrated in
figure 7 for crop season and figure 8 for varietal
type.

Table 15. Components of variance and covariance of grain yield and protein content of rice.

Degrees
Component of
freedom

Brown rice protein
Variance cv (%) Contribution (%)

Grain yield
Variance cv (%) Contribution (%)

Grain yield x protein
Covariance Contribution (%)

STATISTICS 43

Variety 10 0.42418 7.0 16.1 0.56219 19.3 26.4 0.08757 -14.5
Environment 15 1.82589 14.6 69.4 1.20345 28.2 56.5 .48394 80.0
Variety x
environment 150 0.37812 6.6 14.5 0.36227 15.5 17.1 .20932 34.5

Grain yield (t/ha)
81

0 50 100 150 200

TYPE B

0 50 100 150
Nitrogen applied (kg/ha)

50 100 150

5. Three major types of nitrogen response curves of rice.

SOIL HETEROGENEITY
Planting an area to varieties differing in growth
duration by more than 10 days increases soil
heterogeneity in the following season (1972
Annual Report). This year, we evaluated the
effect of growing varieties differing in both
growth duration and tillering ability under
different plant spacings.
In the 1972 wet season, IR8, C4-63G, IR478-
68-2, IR127-80-1, IR1561-228-3, and IR747B2-
6-3, were grown under three plant spacings,
10 x 10 cm, 20 x 20 cm, and 30 x 30 cm, in
three replications. In 1973 dry season, IR127-
80-1, IR841-5-1, Ratna, and IR1561-228-3, were
grown at 10 x 10 cm, 20 x 20 cm, and 30 x 30
cm in 11 replications. In the season following

each of these plantings, IR1514A-E597 was
grown throughout each area.
The dry season data indicated some differences
in grain yields from plots planted to the six
varieties in the previous wet season (Table 16).
Yields of IR1514A-E597 from plots in which
IR747B2-6-3 (having the shortest growth dura-
tion) had been grown previously were the highest,
even though IR747B2-6-3 had the largest tiller
number. Difference in tillering ability did not
seem to give appreciable residual effect relative
to growth duration.
On the other hand, in the wet season trial
where the four varieties tested not only had a
longer growth duration but also a smaller range
of growth duration than the six varieties in the
1972 dry season trial, there was no significant

Frequency (%)

X=I82

,
I I I

0 50 100 150 200 0 2 4 6 8 10 0 3 9 15 21 27 33 39
N max ( kg/ ha ) Yax (t / ha) YI ( kg grain/kg N)
6. Frequency distribution of three nitrogen response parameters, based on 564 response curves of different varieties grown
under varying conditions, by crop season. 1966-1972.

44 IRRI ANNUAL REPORT FOR 1973

-0 XR=12
X=75
5 et I
o sV sDry
I season
5 /
*- y r
0 -

Grain yield (t/ha)
7

6 '

0 50 100 150 200
Nitrogen applied ( kg / ha )
7. Estimated nitrogen response of rice for dry and wet season
crops, based on data from 564 response curves of different
varieties grown under varying conditions. 1966-1972.

difference among yields from areas planted to
different varieties in the previous season. Grain
yields from areas having different plant densities
in the previous crops were significantly different,
however, 10 x 10 cm giving the lowest yield
although average yield reduction was only about
0.2 t/ha. On the other hand, there was no signifi-
cant difference between 20 x 20 cm and 30 x 30
cm spacings.

EXPERIMENTAL DESIGNS FOR MULTIPLE
CROPPING
Most statistical procedures developed for agri-
cultural research are primarily meant for experi-
ments involving single crops. Multiple cropping
technology, however, requires the simultaneous
testing and evaluation of several crops following
a prescribed combination or sequence of plant-
ing. Thus, instead of being concerned only with
environmental factors surrounding a single crop,
multiple cropping research demands a technique
by which many types of crops and crop
sequences can be tested under varying environ-
ments. Three major difficulties are encountered
in multiple cropping experiments. First, since
crop combinations and crop sequences usually
have large interactions among themselves as well
as with environmental factors, multi-factor
experiments involving a large number of treat-

Grain yield (t/ha)
8
DRY SEASON

Improved variety
6

Non-improved variety 4'
2

o I
6
WET SEASON

4

2

0 ---- I ----- I ----- I ---
0 50 100 150 200
Nitrogen applied (kg/ha)
8. Average nitrogen responses for improved and non-
improved varieties based on 195 response curves, by crop
season. 1966-1972.

ments are generally undertaken. Second, large
experimental error can be expected when several
crops which differ in plot techniques and cultural
requirements are tested together. Third, since
economic data are much more important in the
evaluation of multiple cropping systems than in
single-crop experiments, the experimental pro-
cedure must conveniently permit measurement
of economic data.
To cope with the large number of multi-factor
treatments involved in a multiple cropping trial,
we developed a modification of the standard
fractional factorial design for a test which was
conducted by the multiple cropping department
in 1973 dry season. The test involved 63 inter-

STATISTICS 45

Table 16. Grain yield of IR1514A-E597 (unfertilized) grown in areas previously planted to varieties differing in growth
duration and tiller number under three plant spacings. IRRI, 1973.

Variety planted in previous crop Yield (t/ha) of IR1514A-E597

Designation Tillers Growth duration Spacing in previous crop (cm)
(no./hill) (DTa) 10 x 10 20 x 20 30 x 30
Dry season
IR747B2-6-3 15 88 3.63 3.79 3.60
IR1561-228-3 15 96 3.52 3.48 3.64
IR127-80-1 9 109 3.15 3.19 3.79
IR478-68-2 9 112 3.41 3.41 3.31
C4-63G 10 115 3.39 3.44 3.28
IR8 11 115 3.39 3.49 3.61
Avgc 3.41 a 3.47 a 3.54 a
Wet season
IR1561-228-3 15 94 3.14 3.30 3.35
Ratna 13 90 3.18 3.32 3.48
IR127-80-1 9 109 3.14 3.22 3.23
IR841-5-1 11 111 3.16 3.45 3.42
Avgc 3.15 b 3.32 ab 3.37 a

aDays after transplanting. bThree replications. cMeans followed by a common letter are not significantly different at the 5% level. dl 1
replications.

cropping systems (composed of three crops-
mung, sweet potato, and peanut-grown singly
or intercropped at different durations of overlap
and under sevon planting arrangements of corn)
tested under three fertilizer levels and four weed
control levels. Over 750 treatment combinations
were possible, but our suggested design consisted
of only 256 treatments, half of which were
replicated while the rest had no replication. The
evaluation of the design showed its potential for
reducing the number of treatments to a manage-

able size without losing information on some
important interactions.
Although the measurement of economic data
may require plot sizes larger than that of agrono-
mic data, replication may not be necessary for
achieving the required precision in the former.
Thus more than one plot size should be used in
a trial-larger plots (without replication) for the
collection of economic and agronomic data, and
smaller plots (with replications) for agronomic
data.

46 IRRI ANNUAL REPORT FOR 1973

P l n t The grain yield of an early maturing line,
P la n IR747B2, planted year-round at Los Bafios

p h y s i o related with solar radiation
and negatively correlated
with daily mean temperature during the 25-day period before flower-
ing. The derived formula of climatic productivity index predicts that a
combination of high solar radiation and low daily mean temperature
will give high yields. D Under moisture stress conditions, stomates of
rice leaves are closed on sunny days, photosynthetic activity reaches a
low plateau at low sunlight intensity, hence a considerable portion of
the strong sunlight is wasted. Large varietal differences were found in
cuticular resistance, which could be used as one of the criteria for
drought-resistant varieties. Increasing the tiller number or leaf area for
greater yield potential will make upland varieties more susceptible to
drought unless the increase is accompanied by other factors which will
increase drought resistance. O Further studies on varietal difference in
net assimilation rate indicate that large difference exists only under
strong sunlight. O A survey of the flood damage in the Philippines
confirmed our earlier laboratory findings-the longer the duration of
submergence and the younger the plants, the lower is the relative
survival and the greater the damage. O Studies on the biology of S.
Maritimus showed that flowering can be induced by cutting the 140-day-
old plants, coinciding with the rice harvest. This weed grows at a faster
rate than rice. The growth is very sensitive to light intensity.

CLIMATIC INFLUENCE ON YIELD
In past studies, great emphasis was placed on
effect of solar radiation on ripening and hence
rice yield. In our analysis of grain yield of IR8,
however, grain number per square meter was
highly correlated with yield, and there was not
much variation in filled-grain percentage or
1,000-grain weight (1968 Annual Report). Since
grain number is determined before flowering, it
is logical to examine climatic influences on grain
number as well as on grain filling.
In the past, the effect of temperature on grain
number has been totally neglected. Controlled
environment studies, however, have shown that
temperature during panicle development affects
grain number (1972 Annual Report).
To examine climatic influence on yield com-
ponents and yield, an early maturing line,
IR747B2-6, was planted in the field every 2
weeks, giving 26 crops in 1 year from July 1972.
Seven crops were excluded from the analysis
because of severe lodging and damage by diseases
and insects.
Growth characteristics of IR747B2-6.
IR747B2-6 matures in 96 days from sowing to
harvest at Los Bafios throughout the year. It
develops 13 leaves on the main culm (fig. 1).
Panicle initiation occurs about 20 days before
flowering. The estimated date for necknode
differentiation stage is 25 days before flowering,
about 7 to 8 days later than that for medium-
maturing varieties. At 10 x 10 cm spacing and
with 100 kg/ha N, it develops sufficient leaf area
index and enough tillers for maximum yield
(1970 Annual Report).
Yield and yield components. Grain yields of 19
crops (fig. 2) ranged from 4.6 to 7.1 t/ha. Plant-
ings from December through March gave high
yields. Grain yields were highly correlated with
total dry weight (r = 0.856**), indicating that
high photosynthetic production was simply
related to high grain yield. Grain yield of rice
can be expressed: Y = NFW x 10- where Yis
grain yield (t/ha), N is grain number per square
meter, F is filled grain percentage, and W is
1,000-grain weight. Under normal weather
conditions, grain number is determined before
flowering, 1,000-grain weight is determined
partially before and partially after flowering, and

filled grain percentage is determined at and after
flowering. Among the yield components meas-
ured, grain number per square meter was most
variable, 1,000-grain weight was somewhat vari-
able, and filled-grain percentage was fairly con-
stant.
Multiple regression analysis indicated that
81.4 percent of the total variation in yield could

Leaves (no/main culm)

12
12 _-
-

4 -

I I I

Til

U
Leaf area index
0o

6 -
6
4

2
0 I
ters (no./sq m)

600 I

Total dry wt ( kg/sq m)

0 20 40 60 80 100
Days from seeding
1. Growth process of IR747B2-6 planted at 10 x 10 cm
spacing with 100 kg/ha N at IRRI.

48 IRRI ANNUAL REPORT FOR 1973

800

be explained by N, F, and W. The relative
importance of the three variables, as evaluated
from standard partial regression coefficients, was
0.614 for N, 0.212 for F, and 0.345 for W. Thus,
grain number per square meter is almost twice
as important as grain weight and approximately
three times as important as filled-grain percent-
age in estimating yield.
By means of correlation coefficients as well as
multiple regression analysis, we computed the
percentage contribution of yield components,
individually or in combination, to yield. N alone
explained 60% of yield variation (Table 1)
while the combination of all the yield compo-
nents accounted for 81% of yield variation:
Fand Wtogether accounted for only 21 %. If the
contribution of all the yield components is taken
as 100, which would be true if there were no error
in measurement, the contribution of N becomes
74 percent. Thus grain number clearly was the
most important yield component limiting yield
in this experiment.
Climatic influence on yield. To examine effects
of solar radiation and temperature on yield and
yield components, the growth of the IR747 line
was divided into three 25-day periods: 1) trans-
planting to necknode differentiation, 2) neck-
node differentiation to flowering, 3) flowering to
maturity.
We found a high correlation between grain
number per square meter (N) and solar radiation
during period 2 (S2) and temperature during
period 2 (T2) (fig. 3). This relationship can be
written N/S2 = f(T) = 278-7.07 T2. This
equation implies that grain number per square
meter is positively correlated with solar radiation
during period 2, that is, 25 days before flowering,
and negatively with daily mean temperature
during the same period. The negative correlation
between grain number and temperature agrees
well with the results of controlled environment
studies (1972 Annual Report). The above
equation is rewritten N = f(S, T) = S2 (278-
7.07 T2). This implies that grain number of the
IR747 line can be estimated in terms of solar
radiation and temperature. Since grain number
determines potential grain yield, the proposed
function, f(S, T), is called potential climatic
productivity index. The correlation coefficient
between measured grain number and potential

Yield (t/ha)
8
L Damaged
S crops I

Harvest
2. Grain yields of IR747B2-6 planted every 2 weeks. Shaded
crops were damaged by lodging, insects, and diseases. IRRI,
1972 to 1973.

climatic productivity index was 0.888**.
Using 18.1 g for 1,000-grain weight and 86
percent filled grains (the mean values of the 19
crops in this experiment), we can estimate grain
yield of the IR747 line: Y = S2 (278-7.07 T2).
0.86 18.1 10-5. Since the computed yield is
expressed in terms of solar radiation and temp-
erature, it is called climatic productivity index.
This index is highly correlated with actually
measured yield (fig. 4) which implies that yield
of the IR747 line at Los Bafios is positively cor-
related with daily solar radiation and negatively
with daily mean temperature during the 25-day

Table 1. Contribution of each yield component to grain
yield.

Variab Contribution to total
Variablesa
variation in yield (%)
N 60.2
F 21.2
N and F 75.7
N and W 78.5
N and F and W 81.4
aN = grain number per square meter; F = filled grain percen-
tage; W = 1,000 grain weight.

PLANT PHYSIOLOGY 49

110 -

100 -

90-

80-

70-

60
0O-

0 24 25 26 27 28 29
Temperature (*C)
3. Grain number per square meter (N) and solar radiation
(S2) in relation to daily mean temperature during the period
of 25 days before flowering.

period before flowering. We also obtained a high
correlation between grain yield and solar radia-
tion during the ripening period (r = 0.834**).
Although many workers have reached the same
result, we found that solar radiation during the
ripening period is highly correlated also with
potential climatic productivity index in our
experiment at Los Bafios (r = 0.831**). Thus
the high correlation between yield and solar
radiation during ripening period may be only
superficial.
To examine direct effect of solar radiation on
yield, the correlation coefficient was computed
for ripening grade and solar radiation during
ripening period. Ripening grade is the product of
filled grain percentage and 1,000-grain weight,
and is considered a good indication of degree of
ripening. Ripening grade, however, was loosely
correlated with solar radiation during ripening
period (fig. 5).
The evidence seems to indicate that grain
number is the most important factor limiting
grain yield, and it is highly correlated with solar
radiation and temperature during the 25-day
period before flowering, that is, from necknode

Grain yield (t/ho )
81

4

Y = 278 -707 X
r = 0829**

*

50 IRRI ANNUAL REPORT FOR 1973

Y 1.3 + 0.81 X
r 0.901 *

* 0

* /*

4t-
0 T1. I I I I
0 4 5 6 7 8
Climatic productivity index (t/ha)
4. Grain yield in relation to climatic productivity index.

differentiation to flowering. Solar radiation
during the ripening period has a slight effect on
ripening, but less than previously believed. This
conclusion seems to be valid when daily solar
radiation is more than 300 cal cm- 2 day-.
In our experiment, the size of sink (grain
number) was most limiting to grain yield, and
hence solar radiation and temperature during
the period when the sink size is determined are
the strongest influences on grain yield at Los
Bafios.
A combination of high solar radiation and
low temperature gives high grain yields (fig. 6).
The concept of climatic productivity index pro-
vides a way to assess relative rice productivity
for different localities under different climatic
environments.

PHYSIOLOGY OF DROUGHT RESISTANCE
Leaf resistance and moisture stress. Under most
conditions the major path of water loss by the
plant is stomatal transpiration. Stomatal trans-
piration is controlled by stomatal aperture which
is in turn regulated by light and moisture supply.
To study relationships between leaf resistance
(combined resistance of stomates and cuticle),
moisture stress, and solar radiation, IR5 plants

0
*

I-.

I-.. I

Table 2. Effect of moisture stress on dry weight of different plant parts, number of tillers, plant height, and leaf areaa

Field moisture capacity Dry wt (g/pot) Tillers Plant ht Leaf area
during treatment (%) Leaf Culm Root Total (no.) (cm) (sq cm)

21.1 29.9
4.7 22.4
0.6 16.6
6.3 8.6

'Plants under upland conditions were grown at near-field capacity for the first 35 days and then subjected to the specified soil moisture
stress for 3 weeks.

were grown in pots under flooded and upland
conditions at near-field capacity for 35 days. The
plants grown under upland conditions were then
subjected to one of three water regimes-70 per-
cent, 50 percent, or 35 percent of field moisture
capacity-for 3 weeks. Plants under flooded
conditions were allowed to continue to grow
normally for the same period.
The 3-week moisture stress greatly affected
leaf area and dry weight (Table 2). Plant height
and tiller number were less affected.
On cloudy days, visible symptoms of moisture
stress occurred only on plants grown at 35 per-
cent of field moisture capacity while on sunny
days all the plants grown under any moisture
stress level showed some visible signs early or
late in the day. Diurnal changes in leaf resistance
of the second fully developed leaf on the main
shoot were measured with a diffusive porometer
on cloudy and sunny days during the stress
period.
The diurnal changes in leaf resistance of the
plant grown in flooded soils had a similar pattern
regardless of weather conditions (fig. 7). The leaf
resistance values were high early in the morning
and late in the afternoon. During the daytime,
the leaf resistance values remained low, around

Ripening grade
18 -
Y = 13.1+ 0.00656 X

15 -

14 -
O I 1 I I I I
O300 350 400 450 500 550
Solar radiation (cal* cm2 day- )
5. Ripening grade in relation to solar radiation during
ripening period. Ripening grade is the product of filled-grain
percentage and 1,000-grain weight.

2.5 to 5.0 s/cm. This implies that the rice plants
grown in the flooded soil had little or no moisture
stress, and hence the stomates were open during
the daytime. Under such conditions, the plants
may use solar radiation for photosynthesis at
maximum efficiency. The plants grown under
upland water regimes showed similar diurnal
changes in leaf resistance on very cloudy days.
On sunny days, however, leaf resistance values
of those plants started rising rapidly in the after-
noon or even in the morning depending on
weather conditions. These measurements show
that even under the same soil water regime,

Climatic productivity index ( t/ha )
8 1

0 25 27 29
Temperature (C)
6. Climatic productivity index in relation to solar radiation
and daily mean temperature during the period of 25 days
before flowering.

PLANT PHYSIOLOGY 51

Flooded
70
50
35

Leaf resistance ( s/cm)

0400 0800 1200 1600

0400
Time

0800 1200 1600

7. Diurnal changes in leaf resistance (IR5) on August 4, 1973 (cloudy) and August 7 (sunny) in plants subjected to different
levels of field moisture capacity (FMC).

plants are subjected to more severe moisture
stress on sunny days than on cloudy days. Thus,
under conditions of moisture stress, a high level
of solar radiation will induce stomatal closure
during the daytime, and hence radiation will not
be used by the plant for photosynthesis. There-
fore, relationship between solar radiation and
plant growth in flooded conditions should be
quite different from the relationship under moist-
ure stress. Under flooded conditions, increasing
amounts of incident solar radiation will increase
plant growth. Under moisture stress, however,
high solar radiation will not have a favorable
effect on plant growth. Based on theoretical
consideration of the light-photosynthesis curve,
it is more likely that moderate incident solar
radiation is more favorable for plant growth than
high solar radiation. Thus, upland rice culture
in partial shade such as under coconut trees
merits more attention.
Photosynthesis under moisture stress. Since
leaf resistance increases under moisture stress,
photosynthesis, or intake of CO2 which occurs

through stomates on leaves, and transpiration
should be affected by increased leaf resistance
under moisture stress. To study how internal
moisture stress affects photosynthesis of rice
leaves, we grew IR5 plants in pots for 34 days
with sufficient water and then induced moisture
stress by withholding water from the pots. Leaf
resistance was taken as an indication of internal
moisture stress and measured with a diffusive
porometer. The measured resistance values were
multiplied by 1.71 to obtain the resistance to
carbon dioxide.
Both the maximum photosynthetic rate and
the saturation light intensity varied with varying
leaf resistance (fig. 8) with increased leaf resist-
ance, the photosynthetic rates reached maxi-
mums at low light intensities and the maximums
were lower than those with less leaf resistance.
This implies that high solar radiation is not fully
used for photosynthesis under moisture stress.
In other words, a large proportion of strong
sunlight is wasted under moisture stress. Strong
sunlight may even have adverse effects on rice

52 IRRI ANNUAL REPORT FOR 1973

AUGUST 7

I I I I I I

growth by raising leaf temperature and by
inducing stomatal closure early in the day.
Leaf rolling and moisture stress. A rice leaf
rolls under soil moisture stress. Hence, leaf
rolling indicates internal moisture stress for a
variety. But under the same soil moisture stress
one variety may roll its leaves while another does
not. To examine leaf rolling of different varieties
under the same soil moisture stress, two varieties
were grown in the same pot. Water was withheld
from the pots to induce internal moisture stress.
Degree of leaf rolling was recorded along with
measurement of leaf resistance (Table 3). Leaves
of 81B25 were rolled without moisture stress.
This was confirmed by measurement of leaf
resistance. Under severe moisture stress, as
indicated by high leaf resistance, degree of leaf
rolling varied: 81B25 rolled more than IR20,
MI-48 rolled more than IR5.
If different degrees of leaf rolling occurs at a
similar leaf resistance as we observed in this
experiment, leaf rolling could be regarded as a
desirable character for drought-resistant vari-
eties. Leaf rolling should decrease transpiration
loss, thus conserving moisture in the soil.
Plant changes induced by moisture stress. A
series of physiological events occurs when the
rice plant is subjected to moisture stress (Table
4). Except for sterility, all characters are highly
dynamic and hence reversible. Once moisture
stress is relieved, most characters return to
normal conditions. Therefore, moisture stress

Table 3. Leaf rolling and leaf resistance of four varieties
grown in pots.
Water Leaf Leaf
Variety withheld resistance rolling
(days) (s/cm)
Pot A
IR20 1 2.5 None
2 2.8 None
3 61.0 Half
81 25 1 2.8 Slight
2 3.9 Slight
3 80.0 Complete
Pot B
IR5 1 3.4 None
2 3.9 None
3 75.0 Slight
M1-48 1 5.1 None
2 6.9 None
3 79.0 Complete

0 20 40 60 80
Light intensity (klx)
8. Photosynthetic rates of rice leaves under moisture stress
at different light intensities (r, = resistance).

around flowering time, which induces high
sterility, is the most critical for rice yield.

SCREENING FOR DROUGHT RESISTANCE

Field assessment. To determine varietal differ-
ences in drought resistance under the field
conditions, we grew 20 varieties at the IRRI farm
under three water regimes. The degree of mois-
ture stress was varied by changing frequency of
irrigation. Plant height under moisture stress
relative to that under no moisture stress was

Table 4. Physiological and morphological changes
induced by moisture stress.

Without With
Feature moisture moisture
stress stress
Visible features
Plant height Normal Reduced
Tiller Normal Reduced
Leaf area Normal Reduced
Leaf rolling No Yes
Sterility Low High
Non-visible features
Stomates Open Closed
Major path Stomatal Cuticular
of water loss transpiration transpiration
Leaf water potential High Low
Leaf temperature Low High
Heat tolerance Low High
Photosynthesis High Low
Proline content Low High

PLANT PHYSIOLOGY 53

Table 5. Drought resistance of 20 varieties as assessed
by plant height reduction under moisture stress in
field, IRRI, 1973 dry season.

Plant ht (cm)a Relative plant htb
Designation
No Moderate Severe Mean
stress stress stress
E425 75 79 77 78
Miltex 86 77 68 73
M1-48 107 72 69 71
Jappeni Tungkungo 92 68 73 71
OS4 89 68 67 68
Palawan 97 69 66 68
Dular 96 70 61 66
Rikuto Norin 21 85 74 57 66
PI215936 55 74 58 66
Azucena 105 67 61 64
Azmil 88 73 54 64
IR5 62 70 56 63
1R127-80-1 84 69 52 61
81B25 88 65 54 60
IR442-2-58 66 60 57 59
NARB 96 61 52 57
IR8 62 61 47 54
IR1529-680-3 65 60 47 54
IR841-67-1 62 57 48 53
IR20 64 57 44 51

aMeasured 41 days after sowing. bTaking plant height at no
moisture stress as 100.

taken as a measure of drought resistance. Plant
height is one of the plant characters most
sensitive to moisture stress.
Most upland varieties seemed to be more
resistant to drought than lowland varieties
(Table 5). Among lowland varieties, IR5 can be
regarded as relatively resistant and IR20, as very
susceptible. These results seem to agree well with
those obtained by the varietal improvement
department. Some physiological characters,
such as heat tolerance and quick closure of
stomates in response to moisture stress, confirm
that E425, M1-48, OS4, and Palawan are
resistant and IR20 is susceptible (1972 Annual
Report).
Cuticular resistance. High cuticular resistance
of the leaf surface is a desirable characteristic for
drought resistance because when stomates are
closed under moisture stress, cuticular trans-
piration becomes the major path of water loss by
the plant. Significant differences exist in cuticular
resistance among plant species. In general,
aquatic species which live in water have small
resistance values while xerophytic species that
are adapted to dry climates have high values of

resistance. The cuticular resistance values of
mesophytes, to which most crop species belong,
come in between the above two. Little attention
has been paid to varietal difference in cuticular
resistance for a given species. Since rice grows
under diverse water regimes from upland to
flooded conditions, a large variation in cuticular
resistance may exist among varieties and this
difference might be related in part to drought
resistance of rice varieties.
Measuring cuticular resistance of rice leaves
is difficult because the rice plant has stomates on
both sides of its leaves. We measured cuticular
resistance with a diffusive porometer in the dark
and when the plant was fully turgid.
The cuticular resistance values of 35 rice vari-
eties varied from 30 to 68 s/cm (Table 6). Some
varieties that perform well under upland condi-
tions showed high cuticular resistance values.
These were Azmil, Rikuto Norin 21, several
RP-79 lines, Azucena, M1-48, IR442-2-58, Bala,
and IR5. On the other hand, some upland vari-
eties such as Palawan, E425, Miltex, and OS4
had a low cuticular resistance. Among these
varieties, Palawan and OS4 are known to have
longer and more branched roots. It is not sur-
prising that more than two mechanisms confer
drought resistance.
Sorghum and corn are known to be much more
resistant to drought than rice. Indeed, sorghum
and corn have higher cuticular resistance values
(Table 6). Their cuticular transpiration is only
one-half to one-fourth that of rice varieties.
The measurements of the cuticular resistance
of rice varieties indicate that there is a consider-
able variation in cuticular resistance of rice
leaves among varieties, and high cuticular
resistance accounts in part for the resistance of
rice varieties to drought. It should be desirable
to combine cuticular resistance with long and
well-branched roots in one variety.
Proline assay. The proline content of plant
tissues increases when plants are subjected to
moisture stress. Therefore, increase in proline
content can be an indication of physiological
dryness. In barley, increase in proline content
in leaf tissues is positively correlated with
drought resistance.
In a preliminary study to see if proline assay
can be used for screening drought-resistant rice

54 IRRI ANNUAL REPORT FOR 1973

Table 6. Cuticular resistance of 35 rice varieties, and
sorghum and corn.

Variety

Sorghum (Cosor 3)
Corn (Early Thai composite)
Azmil
Rikuto Norin 21
RP-79-19
RP-79-14
RP-79-13
RP-79-1 6
Azucena
NARB
RP-79-23
M1-48
IR442-2-58
Bala
Sigadis
Taichung Native 1
IR5
N-22
RP-8-8
IR841-67-1
RP-7-2
IR1 529-680-3
IR1 561-228-3
Jappeni Tungkungo
IR26
IR8
81B25
1R1541-76-3
IR24
PI-215936
Palawan
IR127-80-1
E425
IR20
Dular
Miltex
OS4

Cuticular
resistance
(s/cm)
116
112
68
66
66
63
60
60
60
58
57
56
54
51
49
49
48
47
47
47
44
43
43
42
41
37
37
36
35
35
33
33
33
32
30
30
30

varieties, we examined increase in proline con-
tent in rice leaves in response to moisture stress.
We found that proline content in leaves of
intact plants (IR747B2-6) increased from 50 pg/g
fresh weight without moisture stress to about
7,000 pg/g under severe moisture stress.
Technically, it is difficult to subject many
intact plants to the same degree of moisture
stress at one time. To simplify the technique of
stress induction we examined use of leaf seg-
ments. Rice leaves were cut into 1-cm segments
and 0.5 g of the leaf segments was placed in a
petri dish containing nutrient solution plus
polyethylene glycol for about 24 hours. The
amount of polyethylene glycol added to nutrient

solution specifies the water potential of the
system, a measure of moisture stress. Proline
content in leaf segments did not increase down
to -2 bars but below that proline content in-
creased sharply with decreasing water potential
(fig. 9).

PHOTOSYNTHESIS

Varietal difference in net assimilation rate. Vari-
etal differences in the net assimilation rate of 12
varieties selected from 313 varieties (1972 Annual
Report) were further tested under high and low
solar radiation (Table 7). Varietal differences
were clearer under high solar radiation than
under low solar radiation. CP231 and Molaga
Samba G18 showed consistently high net assimi-
lation rates under both high and low solar
radiation. BJ1 grew very vigorously and still had
a high net assimilation rate. High net assimila-
tion rates were closely correlated with nitrogen
content per unit leaf area. The effect of solar
radiation on specific leaf weight was also very
clear. Specific leaf weight became much smaller
under a low solar radiation than under a high
solar radiation. In other words, the leaves be-
came much thinner which, in turn, was cor-
related with lower net assimilation rate under a
low solar radiation.

Proline content (.ug/g fresh wt)

0 -4 -8 -12 -16
Water potential (bars)
9. Accumulation of proline in rice leaf segments when
floating in polyethylene glycol solutions of different water
potentials.

PLANT PHYSIOLOGY 55

Table 7. Net assimilation rate (NAR). nitrogen content per unit leaf area (N), and specific leaf weight (SLW) of 12
selected varieties under high and low solar radiation.

Variety

CP231
Molaga Samba G18
BJ1
Siam
IR747B2
MTV7
Gend Jah Banten
Zenith
IR5
Sigadis
0. glaberrima' (Acc. 100932)
0. glaberrima' (Acc. 100989)

NA
(mg cm-2
2.0(
1.91
1.71
1.7'
1.55
1.5(
1.44
1.44
1.42
1.4C
1.38
1.3C

At high solar radiationa
R N
Sday-') (mg/dm')
0 24
6 20
6 20
4 20
5 19
) 17
1 19
19
18
16
16
14

At low

SLW NAR
(mg/cm') (mg cm-2 day-')
4.6 0.94
3.7 .97
3.9 .76
3.7 .80
3.4 .79
3.2 .78
3.6 .86
3.3 .87
3.1 .84
3.0 .77
3.2 .82
2.9 .71

'475 cal cm-'2 day-'. b284 cal cm-' -day'.

Nitrogen nutrition and stomatal resistance.
Nitrogen application affects photosynthesis by
increasing leaf area and maintaining high photo-
synthetic rate per unit leaf area. To study the
second function of nitrogen, we grew IR8 in
culture solution at a low and a high nitrogen
concentration. We measured photosynthetic
rate, specific leaf weight, nitrogen content per
unit leaf area, and leaf area. We also measured
changes in stomatal resistance as affected by
nitrogen nutrition. Specific leaf weight of fully
developed leaves was not affected by nitrogen
supply (Table 8). Nitrogen supply changed
nitrogen content per unit leaf area, which in turn
was closely correlated with photosynthetic rate.
Using the second leaf, we found that stomatal
resistance of the leaf was not affected by nitrogen
supply. This suggests that photosynthetic rate
of young rice leaves is simply related to nitrogen
content per unit leaf area, and not to either
specific leaf weight or stomatal control. With
the fourth leaf, however, low nitrogen supply
decreased nitrogen content per leaf area, but
increased stomatal resistance. High nitrogen
supply had reverse effects. Stomatal behavior in
rice leaves apparently is partly controlled by
nitrogen nutrition. Thus, in rice, nitrogen con-
tent per unit leaf area, is the most useful para-
meter relating to photosynthetic rate. This
experiment demonstrated that nitrogen nutri-
tion has a pronounced effect on photosynthetic

rate of a rice leaf even after it has been fully
developed.
Soil carbon dioxide flux and rice photosynthesis.
In field photosynthesis, the atmosphere and the
soil are the source of CO2. We estimated the
contribution of soil CO2 to the photosynthesis
of rice when the field was kept flooded and when
it was drained.
Soil CO2 flux was increased by drainage (Table
9). Estimated contribution of soil CO2 to gross
photosynthesis was 5 percent for the flooded
plots and 7 percent for the drained plots. The
effect of drainage may in part account for the
"mid-season drainage" effect on rice yield. The
contribution of soil CO2 could be greater when
a soil is higher in organic matter content or when
crop growth rate is smaller on cloudy days. The
results of this experiment along with other
information indicate that the atmosphere is the
most important source of CO2 for photosyn-
thesis of the rice plant, soil CO2 released into
atmosphere is of secondary importance, and
CO2 absorbed by roots is the least important.

NITROGEN FERTILIZERS AND
NUTRITIONAL DISORDERS

Zinc deficiency or sulfur deficiency may be
induced by continuous and intensive rice crop-
ping in a field. Since different nitrogen fertilizers
have different chemical compositions, they may

56 IRRI ANNUAL REPORT FOR 1973

solar radiation
N
(mg/dm')
16
13
14
14
12
14
14
14
13
12
12
10

SLW
(mg/cm2)
3.1
2.7
2.6
2.8
2.6
2.7
2.9
2.6
2.4
2.4
2.4
2.2

---

Table 8. Effect of nitrogen supply on photosynthesis and stomatal resistance of single leaves.
Photosynthetic rate Stomatal resistance Specific leaf wt Nitrogen content of leaf
Treatment (mg CO2 .dm-2, h') (s/cm) (mg/cm2) (mg/dm2)
Treatm enta 2 --- -------- --------------
(ppm N) 0 4 7 0 4 7 0 4 7 0 4 7
days days days days days days days days days days days days
Second leaf
10- 10 27.1 24.5 20.4 3.8 4.4 4.1 2.35 2.41 2.27 8.1 7.9 7.0
100-100 43.6 41.6 42.4 3.1 2.7 3.1 2.69 2.85 2.80 15.5 15.5 15.5
100- 0 43.6 34.7 30.8 3.1 4.1 5.5 2.69 2.65 2.56 15.5 11.2 10.6
10-100 27.1 38.8 35.2 3.8 3.2 3.2 2.35 2.50 2.59 8.1 12.1 12.4
Fourth leaf
10- 10 11.4 9.8 15.4 27.5 2.02 2.12 5.8 5.0 -
100-100 37.1 30.8 31.5 3.9 4.6 6.8 2.61 2.83 2.53 14.1 13.5 13.0
100- 0 37.1 17.8 13.8 3.9 12.1 16.2 2.61 2.61 2.42 14.1 8.9 7.7
10-100 11.4 21.3 25.1 15.4 5.0 3.4 2.02 2.37 2.30 5.8 9.6 9.6

aThe plants were grown in culture solutionsof different nitrogen concentrations as indicated inthefirst column for4 weeks and then were
transferred to those as indicated in the second column.

differentially affect the incidence of zinc defici-
ency or sulfur deficiency or other problems.
To test effects of three nitrogen fertilizers,
ammonium sulfate, ammonium chloride, and
urea, on yield, total dry matter production, and
possible nutritional problems, we set up a long-
term field experiment at the IRRI farm. Data on
total dry weight as well as grain yield were col-
lected to provide a realistic measure of photo-
synthetic production.
Grain yield ranged from about 19 to 24 tons
per year while total dry matter production
ranged from about 46 to 51 tons per year (Table
10). Ammonium sulfate produced slightly higher
total dry matter and grain yield than ammonium
chloride or urea. But none of the crops so far had
any visible indication of nutritional problems.

UPLAND RICE
Characteristics of upland rice. The differences
between upland and lowland varieties and the
value of these differences for upland conditions
must be understood in order to improve upland
varieties. We studied nine upland and nine low-

land varieties and found that the upland vari-
eties have certain characteristics distinct from
those of lowland varieties (Table 11). Whether
these characteristics are necessary for drought
tolerance and compatible with requirements
for high grain yields must be evaluated in detail.
The answers may lead to a better understanding
of what the ideal plant type for upland con-
ditions is.
Plant height at harvest. The upland group was
about 36 cm taller than the lowland group. The
height of the upland rice varieties makes them
susceptible to lodging although lodging is not
serious under upland conditions. Tall varieties,
however, may be better able to compete with
weeds, an important problem in upland culture.
With the use of herbicides in modern agriculture,
however, this advantage may no longer be so
great. It is also possible that among the drought-
resistant types, the tall varieties have higher grain
yields.
Tiller number. The upland varieties tested
tended to have fewer tillers than the lowland
varieties. Some workers have recommended
therefore that the tiller number of the upland

Table 9. Carbon balance between rice photosynthesis and soil CO, flux.
Rate (g CH0O m-' day-') Estimated contribution (%) ofsoilCO, to
Soil condition Net dry matter Gross Daytime Net dry matter Gross
production photosynthesis soil CO, flux production photosynthesis
Flooded 22 36 2.0 9 5
Drained 26 44 3.2 12 7

PLANT PHYSIOLOGY 57

Table 10. Grain yield and total dry matter of four continuous crops a year with different kinds of nitrogen fertilizers,
IRRI. 1972 and 1973.

Yield (t/ha) Total dry wt (t/ha)
Crop Month Variety
no. planted Ammonium Ammonium Urea Ammonium Ammonium Urea
sulfate chloride sulfate chloride
1972
1 January IR8 9.1 8.9 8.8 17.9 18.3 17.1
2 May IR747B2-6 4.2 3.7 3.1 10.6 10.2 9.9
3 July IR1561-228-3 6.1 6.1 6.4 12.9 12.9 12.4
4 October IR747B2-6 4.7 4.3 4.5 9.6 8.9 9.1
Total 24.1 23.0 22.8 51.0 50.3 48.5
1973
5 January IR8 7.7 7.6 7.7 16.3 16.0 16.2
6 May IR747B2-6 5.0 4.0 4.2 11.3 11.5 12.0
7 July IR1561-228-3 5.1 4.5 4.8 12.2 11.3 11.7
8 October IR747B2-6 3.3 3.0 3.2 7.2 6.8 7.0
Total 21.1 19.1 19.9 47.0 45.6 46.9

varieties be increased. This recommendation
should be carefully studied since low tiller
number may have a definite advantage when
water stress is severe.
Leaf characters. Upland varieties have fewer
leaves per plant than the lowland varieties, a
consequence of fewer tillers per plant. Upland
varieties also have bigger and thicker leaves than
the lowland varieties. The big leaves possibly
indicate that more photosynthate is available per
tiller of the upland variety, accounting for the
heavier tiller, thicker culm, and taller plant.
The reduction in weight of leaves 2 hours after
detachment showed that the upland varieties
lose moderately less weight than the lowland
varieties. This indicates that upland varieties
have better control of transpiration.
From the few characters measured it is appar-
ent that the upland varieties have definite
characters which distinguish them from the low-
land varieties. These and other characters should
be evaluated carefully in terms of their contribu-
tion to drought tolerance and grain yield.
Leaf area and drought resistance. Leaf area may
be an important aspect of drought resistance in
the existing upland rice varieties. The greater

the transpiring surface of a plant, the more water
that is lost and the greater the effect of moisture
stress on the plant. A large leaf area, however,
does not necessarily mean a high transpiration
rate per plant since the plant may have other
ways to reduce transpiration or increase water-
absorbing capacity.
An experiment was set up to examine leaf
area in relation to plant damage when moisture
stress is imposed. Ml-48, a tall, low-tillering
upland variety, and IR442-2-58, a short, high-
tillering lowland variety which has shown
reasonably high yields under upland conditions,
were used. The leaf area of one set of plants was
reduced by 20 percent by removing all lower
blades. In another set, leaf area was varied by
planting four seeds per pot instead of only one
seed per pot. Watering of the plants was stopped
for 9 days at 40 days after sowing.
Plants in which the leaf area was reduced by
cutting showed moisture stress symptoms much
later than the intact plants. This is mainly the
result of small transpiring surface. Moisture
stress reduced the leaf area of the IR442-2-58
line more than that of Ml-48 (Table 12). With
no stress (control), IR442-2-58 plants whose

Table 11. Differences between upland and lowland rice varieties.

Specific leaf wt Reduction in fresh
Variety Plant ht (cm) Tillers (no./hill) Leaves (no./hill) Leaf size (sq cm) (mg/sq cm) wt of detached leaves (%)
type Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range

Upland 118 107-142 8.6 4.7-19.5 40 25-82 45 29-59 3.05 2.3-3.6 17.5 15.2-24.8
Lowland 82 68-102 182 14.0-23.5 84 70-101 24 19-31 2.67 2.2-3.0 20.7 17.2-23.5
Difference 36" -9.6" -44" 21 0.38" -3.2" -

58 IRRI ANNUAL REPORT FOR 1973

lower blades were removed had a significantly
greater leaf area than comparably treated M1-48
plants, but moisture stress made the leaf areas
the same. Moisture stress also reduced the leaf
area of intact IR442-2-58 plants more than that
of IR442-2-58 plants that had the lower blades
removed.
Thus a large leaf area has little advantage for
plants subjected to moisture stress because
moisture stress reduces the leaf area to a level
comparable to that of varieties that start with
much smaller leaf areas.
Leaf area, especially under field conditions,
can also be changed through the seeding rate.
An increase in tiller number per unit area with
higher seeding rate usually increases the leaf
area. The effect of seeding rate on drought
resistance was tested using one and four seeds
per pot. With no stress, sowing four seeds per
pot was definitely superior to one seed per pot,
as measured by dry matter production at field
capacity. When moisture stress was imposed,
however, plants in the pots with four seeds
showed the symptoms of moisture stress earlier
than the plants in the pots planted with only one
seed. Compared with the corresponding control,
the decrease in dry matter production was 59
percent in the four-seed pots and 45 percent in
the one-seed pots. After the moisture stress
period, the difference in total dry weight be-
tween one and four seeds per pot was insignificant.
For the two plant densities, the decrease in
leaf area as a result of the moisture stress was
higher in the IR442-2-58 line (58%) than in
M1-48 (46 %). Although IR442-2-58 plants had
a larger leaf area before the moisture stress
treatment, afterwards it became smaller than
that of Ml-48. The difference is greater when
based on leaf area per tiller.
Moisture stress decreased the tiller number
per pot regardless of the number of the seedlings
per pot or the variety used. But the four-seed
pots had a relatively larger reduction than the
one-seed pots.
Under moisture stress, IR442-2-58 had more
tillers per unit area than M1-48, but for drought
tolerance high tillering capacity or a high seeding
rate may actually be a disadvantage. Upland
varieties generally have low tiller number. To
increase grain yields, medium-tillering varieties

Table 12. Moisture stress and reduction in leaf area of
plants with intact leaves and plants with 20 percent
reduction in leaf area.

Leaf Leaf areaa (sq cm/hill) Reduction
treatment Moisture stress Control (%)
M1-48
Intact 1410 2780 49
20% removed 1810 2430 26
IR442-2-58
Intact 9840 4300 77
20% removed 1700 4120 59
'LSD (5%) = 540.

are needed. Plant density is usually critical under
upland conditions, however. Since soil moisture
is the main limiting factor under upland condi-
tions, plant density must be adjusted to available
moisture and not to available solar radiation and
nutrients for high yield nor for control of weeds.
Increasing the tiller number or leaf area for
greater yield potential will make the upland
varieties more susceptible to drought unless the
increase is accompanied by other factors that
will increase the variety's water-use efficiency or
resistance to drought.

VOLUNTEER RICE
Effect of planting methods. Previous studies
showed that rice seeds buried in the paddy soil
can germinate and grow as volunteer rice plants
even after three cropping seasons. Our data
showed, however, that volunteer rice will not be
a problem in transplanted rice provided the
volunteer variety and the planted variety do not
have the same plant type and growth duration.
With the mechanization of rice culture, broad-
cast and drilled sowing may become increasingly
widespread. Under these conditions the prob-
lems of volunteer rice may be serious. A field
trial indicated that the competitive character of
volunteer rice is not enhanced by drill-planting
(0.8 volunteer plants/sq m) as compared with the
transplanted method (0.9 plants/sq m). Both
planting methods resulted in less volunteer rice
than the uncropped plot (2.8 plants/sq m). The
volunteer rice plants growing in the cropped
plots had few tillers compared with those grow-
ing in the uncropped plots. The volunteer plants
suffered from competition of the planted rice
crop.

PLANT PHYSIOLOGY 59

	Front Cover
	Half Title
	Title Page
	Table of Contents
	Board of trustees
	Personnel
	About this report
	Research highlights
	Crop weather
	Chemistry
	Multiple cropping
	Statistics
	Plant physiology
	Agronomy
	Soil chemistry
	Soil microbiology
	Plant pathology
	Plant breeding
	Agricultural engineering
	Agricultural economics
	Entomology
	Rice production training and...
	Training programs
	International activities
	Information resources and experimental...
	Publications and seminars
	Index

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