Annual report

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Annual report
International Rice Research Institute
Place of Publication:
Los Baños Philippines
The Institute, 1962-1988.
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27 v. : ill. ; 26 cm.


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Rice -- Research -- Periodicals ( lcsh )
Rice -- Philippines ( lcsh )
serial ( sobekcm )


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Electronic resources created as part of a prototype UF Institutional Repository and Faculty Papers project by the University of Florida.
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The International Rice Research Insitute.

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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 Bahios, Philippines.

The International Rice Research Institute Annual Report for 1973

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


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
2 Grain protein 3 Grain quality
9 Seed and plant metabolism
16 Cropping systems program
16 Lessons from traditional technology 25 Varietal testing of component crops
26 Crop management techniques
28 Agronomic and economic factors
36 Factors limiting farmers' yields
39 Variability in protein content
42 Yield response to nitrogen
44 Soil heterogeneity
45 Designs for multiple cropping trials
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.
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
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


Nyle C. Brady, Ph.D., director Bienvenido 0. Juliana, Ph.D., chemist
Dilbagh S. Athwal, Ph.D., associate director Gloria B. Cagampang, MS., assistant chemist
Marcos R. Vega, Ph.D. assistant director Consuelo M. Perez, MS., senior research assistant
Faustino M. Salacup, B.S., C.P.A., executive officer and BernarditaV Esmama, B.S., research assistant
treasurer Ruth U. Monserrate, B.S., research assistant
Zosimo Q. Pizarro, LL.B. associate executive officer Evelyn P. Navasero, MS., research assistant Pedro G. Banzon, LL.B., administrative associate Adoracion P. Resurreccion, MS., research assistant
Ifor B. Solidum, LL.B., administrative associate* Lyda B. Suzuki, MS. research assistant*
Purita M. Legaspi, B.B.A., C.P.A., assistant treasurer Alicia A. Perdon, U.S., research aide Hermenegildo G. Navarro, B.S., property superintendent Rebecca C. Pascual, M.S., manager, food and dormitory ENTOMOLOGY
services Mano D. Pathak, Ph.D., entomologist
V. Arnold Dyck, Ph.D., associate entomologist
AGRICULTURAL ECONOMICS Fausto L. Andres, U.S., senior research assistant
Randolph Barker, Ph.D., agricultural economist Gerardo B. Aquino, U.S., research assistant
Thomas H. Wickham, Ph.D., associate economist Carlos R. Vega, U.S., research assistant
Robert W. Herdt, Ph.D., visiting agricultural economist Denis T. Encarnacion, B.S_ research assistant Rodolfo D. Reyes, M.S., senior research assistant Tomas D. Cadatal, M.S., research assistant
Teresa L. Anden, A.B., research assistant Caesar D. Pura, MS., research assistant*
Violeta G. Cordova, B.S., research assistant Arlando S. Varca, B.S., research assistant
Ricardo A. Guino, B.S., research assistant Henry C. Dupo, U.S., research assistant
Abraham M. Mandac, B.S., research assistant Gloria C. Orlido, B.S., research assistant
Fe A. Bautista, B.S., research aide Conrado R. Nora, B.S., research assistant
Geronimo E. Dozina, Jr., B.S., research aide Lourdes A. Malabuyoc, B.S., research aide
Oscar B. Giron, B.S. research aide
Eloisa M. Labadan, B.S., research aide EXPERIMENTAL FARM
Adelita C. Palacpac, B.S., research aide Federico V. Ramos, MS., associate agronomist andfarm
Alfredo B. Valera, B.S., research aide superintendent
AGRIULTRALENGNEEINGOrlando G. Santos, B.S., associate farm superintendent AGRICULTURAL ENGINEERINGJunMLaiBSsiofrmupvsr Amir U. Khan, Ph.D., agricultural engineer Juai M. ars, .S. ,farm supervisor
Bart Duff, M.S., associate agricultural economist Filomeno 0. Planting, U.S.,frm supervisor
Fred E. Nichols, B.S., associate evaluation engineer
Joseph K. Campbell, M.S., visiting associate agricultural INFORMATION SERVICES
engineer Steven A. Breth, MA., editor
Jose S. Policarpio, B.S., assistant design engineer* Thomas R. Hargrove, MS., associate editor
Antero S. Manalo, M.S., assistant agricultural engineer Corazhn V. Mendoza, MS., assistant editor Jose R. Arboleda, M.S., senior research assistant Ramiro C. Cabrera, UFA., graphic designer
Nestor C. Navasero, B.S., senior research assistant Arnulfo C. del Rosario, B.S., artist-illustrator
Norberto L. Orcino, B.S., senior research assistant Federico M. Gatmaitan, Jr., artist-illustrator
Consorcio L. Padolina, M.S., senior research assistant Urbito T. Ongleo, U.S., photographer Edgardo G. del Rosario, B.S., research assistant* Feliciano J. Toyhacao, assistant photographer
Guillermo J. Espiritu, B.S., research assistant Simeon N. Lapiz, assistant photographer
Simeon A. Gutierrez, B.S., research assistant Sesinando M. Masajo, B.S., rice information assistant
Zenaida F. Toquero, M.S., research assistant
Ida E. Estioko, B.S., research aide* LIBRARY AND DOCUMENTATION CENTER
Bibiano M. Ramos, B.S., research aide Lina Manalo-Vergara, M.S., chieflibrarian
Benigno T. Samson, B.S., research aide Milagros C. Zamora, MS., assistant librarian
Luzviminda F. Lumang, research aide Mila M. Ramos, ULS., catalog librarian
Benjamin D. Buan, B.S., draftsman Carmelita S. Austria, ULS., order librarian
Fernando S. Cabrales, B.S., draftsman Fe C. Malagayo, ULS., circulation librarian
Feliciano C. Jalotjot, draftsman Rosalinda M. Temprosa, USE., indexer
Jukyu Cho., translator (in Japan) *
AGRONOMY Masatada Oyama, D.Agr., translator (in Japan)*
Surajit K. De Datta, Ph.D., agronomist Mieko Honda, B.A., indexer (in Japan)
Jose A. Malabuyoc, M.S., assistant agronomist Kazuko Morooka, indexer (in Japan)
Jesus T. Magbanua, B.S., senior research assistant*
Pablo M. Zarate, B.S., research assistant MULTIPLE CROPPING
Paul C. Bernasor, B.S., research assistant Richard R. Harwood, Ph.D., agronomist
Rene Q. Lacsina, B.S., research assistant Gordon R. Banta, MS., visiting associate agricultural
Wenceslao P. Abilay, B.S., research assistant economist
Ernesto I. Alvarez, B.S., research assistant Wilhelmino A.T. Herrera, U.S., senior research assistant
Wilma N. Obcemea, B.S., research aide Avelito M. Nadal, U.S., research assistant*
Clarissa G. Custodio, B.S., research aide* Roberto T. Bantilan, U.S., research assistant
Mae T. Villa, R.S., research aide Maximo B. Obusan, B.S., research assistant


Samuel P. Liboon, B.S., research assistant PLANT BREEDING
Manuel C. Palada, M.S., research assistant Gurdev S. Khush, Ph.D.,plant breeder
PLANT PATHOLOGY Te-Tzu Chang, Ph.D., geneticist
Shu-Huang Ou, Ph.D., plant pathologist W. Ronnie Coffman, Ph.D., associate plant breeder
Keh-Chi Ling, Ph.D., plantAntonio T. Perez, Ph.D., assistant visiting scientist Harold E. Kauffman, Ph.D., plant pathologist Rodolfo C. Aquino, MS., assistant plant breeder
Fausto L. NuqueM, ., assistant p athologist Rizal M. Herrera, B.S., senior research assistant
Fauestio Nuquer, MS., assistant platiaologist Jose C. de Jesus, Jr., B.S., senior research assistant
Celestino T. Rivera, M.S., assistant virologist
Jose M. Bandong, M.S., senior research assistant Esperanza H. Bacalangco, B.S., research assistant
Vladimarte M. Aguiero, B.S., research assistant a Cruz, B.S., research assistant Toribio T. Ebron, B.S., research assistant Agapito M. Gonzalvo, Jr., B.S., research assistant
Silvino D. Merca, B.S., research assistant Vicente T. Librojo, Jr., B.S., research assistant
Marina P. Natural, B.S., research assistant* Genoveva C. Loresto, MS., research assistant
Manolito P. Naral, B.S., research assistant Carmen M. Paule, B.S., research assistant
Alberto G. de la Rosa, B.S., research assistant Eugenio S. Surreal, B.S., research assistant
Sonia P. Ebron, B.S .,research aide Oscar 0. Tagumpay, B.S., research assistant
Soni P.Ebro, BS., eserch ideEspiridion T. Torres, B.S., research assistant PLANT PHYSIOLOGY Reynaldo L. Villareal, B.S., research assistant
Shouichi Yoshida, D.Agr., plant physiologist Alicia A. Capital, B.S., research aide
Benito S. Vergara, Ph.D., plant physiologist Angelita P. Marciano, B.S., research aide
Masaki Hara, Ph.D., visiting scientist
Francisco T. Parao, M.S., assistant plant physiologist STAFF IN INTERNATIONAL PROGRAMS Victoria P. Coronel, B.S., research assistant BANGLADESH
Evangelina de los Reyes, B.S., research assistant Rufus K. Walker, MS., rice adviser*
Aurora M. Mazaredo, B.S., research assistant EGYPT
Romeo M. Visperas, B.S., research assistant Kunio Toriyama, D.Agr.Sc., project specialist
Vernon E. Ross, M.S., rice production specialist Emiterio V. Aggasid, B.S., experiment station development
Inocencio C. Bolo, B.S., assistant rice production specialist engineer Eduardo R. Perdon, B.S., assistant rice production specialist Henry M. Beachell, MS., plant breeder Eustacio U. Ramirez, B.S., rice production technician Jerry B. Fitts, Ph.D., agronomist Leopoldo M. Villegas, M.S., rice production technician Russell D. Freed, Ph.D., plant breeder Jose I. Calderon, B.S., rice production technician John M. Green, Ph.D., corn breeder and seed certification
Rizalino T. Dilag, Jr., B.S., rice production technician specialist Leonardo T. Almasan, research aide Robert I. Jackson, Ph.D., joint coordinator, National Rice
SOIL CHEMISTRY Research Program
F. N. Ponnamperuma, Ph.D., soil chemist Cezar P. Mamaril, Ph.D., research administration specialist
Ruby U. Castro, M.S., assistant chemist Jerry L. McIntosh, Ph.D., agronomist
Rhoda S. Lantin, M.S., senior research assistant Richard A. Morris, Ph.D., statistician
Myrna R. Orticio, B.S., research assistant INDIA
Oscar C. Reyes, B.S., research assistant* Reed C. Bunker, Ph.D., entomologist*
Nicolas M. Chavez, B.S., research assistant Wayne H. Freeman, Ph.D., joint coordinator, All-India
Socorro S. Raval, B.S., research assistant Coordinated Rice Improvement Prqiect
SOIL MICROBIOLOGY Ernest W. Nunn, B.S., agricultural engineer*
Tomio Yoshida, Ph.D., soil microbiologist Hiroshi Sakai, Ph.D., plant physiologist*
Hitoichi Shiga, D.Agr., visiting scientist PHILIPPINES
Teresita F. Castro, B.S., senior research assistant Reeshon Feuer, Ph.D., crop production specialist
Diana C. del Rosario, B.S., research assistant SRI LANKA
Wilbur B. Ventura, M.S., research assistant William G. Golden, Jr., M.S., rice specialist
Benjamin C. Padre., Jr., research assistant James E. Wimberly, MS., rice processing adviser
Kwanchai A. Gomez, Ph.D., statistician Robert P. Bosshart, Ph.D., agronomist
Emerito V. Tipa, B.S., research assistant* Dwight G. Kanter, Ph.D., rice breeder
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 *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 International Development Research Centre (Canada), and the Japanese government. 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 PRELUDE 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 worldwide 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 population 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 countrywide 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.


-A r





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.


Rice truly means life itself to the world's poorest and most densely populated regions. RICEA third of mankind-1.3 billion people-depends on rice for more than half of its FOOD OF 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. INCOME
Rice is the primary or secondary staple food of nine-tenths of the low-income people MASSES 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


Index (log scale, 1961= 100)
150 Price (I year later) I

Production I



55 57 59 61 63 65 67 69 71 73

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
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


Diseases Insects Soil problems
Variety Lodging Bacterial Bacterid Grassy Green Brown Stem Alkali Salt Iron ReducBlast b lghtorr stunt Tungro ree injury injury toxicity cts
Ils bl t sreak tut hopper harpper prouuct





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 planthopper 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


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 conditions. 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 interdisciplinary cooperation, which has always been a strong feature of IRRI's rice improvement 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



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 conditions (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.




STUDIES PA= Problem area scientists
IMPROVED (PB) PB= Plant breeders

5. The flow of germ plasm through the GEU.


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 susceptible 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 resistance into new lines so they will remain resistant in different regions and seasons. The line IRI514A-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.


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 resistance 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 (BJl 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


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 nutritional 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.


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 semidwarfs 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 IR1661-1170, IRI531-86-2, IRI646-623-2, and IRI721-11-6. IRI646-623-2 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,


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
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 experiments 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 traditional unimproved lowland rices.


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. Improved 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 highyielding 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 incorporated 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


Soil surface --- -2.5 cm.


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
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
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 perthane, 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


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 directseeded 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 measurement 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 Administration (NIA), the University of the Philippines at Los Bailos 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.


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 determine 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, significant yield increases were obtained from adding either phosphorus or potassium without nitrogen. Such nutritional response to phosphorus or potassium is not common 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 management. 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 slowrelease fertilizers as one dose, even though the split dose requires more labor. Slowrelease 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


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.


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 equipment. 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 versatile 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 subcontracted 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 implements 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.


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 acceptance 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 technology 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 application and cultural practices, which are within the farmer's direct control; environmental 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


9% Insects and
Weed 9% 34 t/ho

Nitrogen Water
21% 26%

73 t/ha 3.9 t/ha

Insects and ---- --
S disease.7sh
Weed 17t/h

Nitrogeen 1ESPTIC

5.0 t/ha 3.3 t/ha

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 others, ctors 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 half a 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


Yield (t/ha)

8 1

Water controI RCE
ERisk, costj


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 favorable 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 Philippine government's successful "Masagana 99" program ("Masagana" means "bountiful 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.


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 seedlings 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 transplantedirrigated 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 Mar Apr May Jun Jul Aug Sep Oct Nov Dec DIRECT SEEDING HARVESTING


60 Bulocon
(27- year overage)


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.


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 following 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 longrange 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


700,0oo ha

UNITED1200000 h 34,000,000 h
740,000 ha 1,500,000 h. 000 ha


5,200,000 o 4,000,0T0 e

,00,000 ha
370000000 ha
6,800,000 h
1,200,000 ha

[I =0,00 h~tres ,200000 0 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 International 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 international 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 Internacional 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 requ,.st 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 scientists. Our scientists at Los Batios serve as "back stop" subject matter specialists when
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.



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

International International
Observational Rice
Nursery Yield

Breeding Programs

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 insecticide 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 OrganiRESEARCH 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 processing and marketing; Indonesia-$90,200 which is part of a 2-year grant for an accelerated 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 22 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.


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 government 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.


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 Cooperative 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.


Crop weather

During 1973, 2,206 mm of rain fell, compared Table 1. Number of rainy days (0.25 mm or more). IRRI,
with the 7-year average of 1,981 mm. Most of the 1966-1972 (avg). 1972, and 1973. rain fell in October, November, and December Rainy days (no.)
while most of last year's rain fell in June, July, Avg 1966-72 1972 1973
and August. Twice as much rain fell during January 13 14 9
October and December this year compared with February 6 4 6
the same months last year. On November 21, 236 March 7 7 7
mm of rain fell in a single day, the largest April 5 9 6
May 16 18 9
amount in 26 years. The rainfall was fairly June 20 18 16
uniform starting in August which helped both July 24 31 19
rainfed lowland and upland rice, which are August 20 21 24
September 22 22 23
entirely dependent on rain for moisture supply. October 18 15 22
There were more rainy days (0.25 mm and November 19 24 21
December 18 11 23
Solar radiation ( kcal cm-2 wk- )
4 1973greater) during August and December this year
than the averages for the previous 7 years (see 3_19W6-72 table). Long-duration rice varieties grown under
upland conditions at IRRI farm were helped by 2 f 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 01 1 year benefited the ripening period environment
Rainfall (mm /wk of the dry-season crop. Because of high rainfall
200 in September and October, solar radiation was
lower this year than last year. In December, there 100 was 4.0 kcal/sq cm less solar radiation than a
year earlier and 2.5 kcal/sq cm less than the 120 1973 December average for the past 7 years. The low
sunlight in December was not harmful to most of 80 a1966ag the wet-season crop, except the very late-maturing crop.
Tropical depressions occurred on October 7, 4v October 24, and November 19 this year. The

0 tropical depression on October 7 caused severe
Jan Feb Mar Apr May June July Aug Sept Oct Nv damage to many wet-season crops which were Solar radiation and rainfall (three-point moving weekly maturing and to those close to harvest. Neveraverage) at IRRI 1973 and 1966172. Shaded area shows the theless, 1973 can be considered a year of few standard deviation of the 71year average, typhoons.


Nutritional studies in preChem istry 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 activity 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. l Parboiling caused a loss of thiamine and a diffusion of thiamine to the endosperm both of which depended on the severity of heat treatment. El 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. El 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. L Starch synthetase bound to the starch granule was solubilized with retention of activity by dispersion of amorphous starch in 75 percent dimethylsulfoxide with ultrasonic waves.

GRAIN PROTEIN In this year's trials three milled rice samples
with 7.7, 10.3, and 11.9 percent protein were
More than 21,000 rice samples from breeding used in a diet which had a constant rice-to-fish and genetic studies were analyzed for Kjeldahl ratio of 100:17. The fish fillet (surgeon, Acanprotein in 1973 as part of a cooperative program tlurus bleaker) had 20 percent protein and 10 to raise the protein content of rice by 2 percen- percent lysine in its protein. Rice was fed at the tage points. daily rate of 10 g/kg body weight. Each diet was
Protein quality. The microbiological quality fed to each child for an adaptation period of 4 of milled rice samples differing in protein con- days, then for 6 days feces and urine were tent was assayed by 0. Mickelsen and D. collected. Composite diets were also analyzed
Makdani (Michigan State University, U.S.A.). for amino acid composition. Each child was fed The growth rate of Streptococcus zymogenes the low protein rice, and then either the high
was used as indicator of protein quality with protein or the intermediate protein rice. Results casein as the standard (100 0). They found that so far indicate that diets with higher rice protein microbiological quality corresponded well with content had a lower chemical score (Table 2). chemical score based on lysine except for the Percentage nitrogen absorption and retention, high value for IR480-5-9 milled rice (Table 1). however, were maintained so that higher protein The correlation coefficient with microbiological content of rice gave a higher value for nitrogen quality was0.86** for chemical score and 0.75* balance. Nitrogen intake was probably madefor protein content. The drop in microbiological equate in the lower protein rice diets and part of value was only about 10 percent for an increase the protein was probably used for energy. The in protein content of over 100 percent. IR8 diet gave the widest range of nitrogen
Nitrogen balance studies in pre-school chil- balance values.
dren were started with C. L. Intengan, Food and High-lysine rice. We previously found that in Nutrition Research Center, Manila. In earlier two successive crops, the varieties ARC 10525 trials in which IR480-5-9 milled rice with 11.9 and Kolamba 540 had 0.5 percentage point percent protein (N x 6.25) was used as the sole higher lysine content of protein than IR8. In the source of protein (mean intake of 314 mg N/kg 1973 dry season, brown rice from the best three body weight daily) for four children, nitrogen single plant selections identified in 1972 from absorption was 75 percent of nitrogen intake and thesevarieties were screened forlKjeldahl protein nitrogen retention was 37 percent of intake. But and dye-binding capacity (lysine) and the best difficulty was encountered because some chil- samples were analyzed for lysine by column dren needed more than three feedings a day to chromatography. We found that the best samreach the required intake of nitrogen. piles still had lysine contents only 0.5 percentage
point higher than that of 1R8 and they were no
Table 1. Biological value of milled rices differing in higher than that of pooled sample. Because of protein content and chemical score of protein based on the limited reproducibility of existing screening relative growth of Streptococcuszymogenes (0. Mickelsen
and D. Makdani, Michigan State Univ., U.S.A.). methods and the inherent variability in lysine content within a variety, attempts to breed high
Protein Lysine Chemical io lysine varieties cannot be justified unless an
Sample (% N x 6.25) (g/16 g N) scored (%) value (%)of percentage point is possible.
Milled rice protein of these two varieties also
Intan 5.97 4.07 74 71.8 had higher lysine content than that of 1R8 rice
IR8 7.69 3.59 65 68.7
IR22 7.88 3.75 68 69.4 (Table 3). Extraction of milled rice protein with
IR22 10.0 3.87 70 70.0 5 percent sodium chloride solution and subIR8 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 fractions revealed that the cause of the higher
BPI-76-1 15.2 3.19 58 63.4 lysine content of ARC 10525 protein was its
aBased on 5.5g lysine/16g N (1973 pattern) as 100%. "Based higher level of salt-soluble protein (specifically on 100% for casein. globulin). Kolamba 540 tended to have a higher


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 absorbed' retained' 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. based 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 perature for 5 minutes, and then cooled in an (residual) protein than IR8. Disc electrophoresis ice-water bath for 15 minutes. Consistency is showed no varietal differences in the protein measured by the length in a test tube of the cold
bands of the soluble protein fractions of the gel held horizontally for 30 minutes or I hour
three varieties. over ruled paper graduated in millimeters (fig. 1).
The coefficient of variability was 4 percent of the
GRAI QUAITYmean of duplicate runs. One hundred samples a GRAIN QUALITYday can readily be run in duplicate by one Gel consistency. A rapid, simple test, which is technician. complementary to the test for amylose content, The consistency values are correlated with
was developed based on the consistency of a cold amylograph setback viscosity (fig. 2) and can 4.4 percent (dry basis) milled-rice paste in 0.20 differentiate three consistency types-high (26 N KOH. This test can be used to distinguish to 35 mm), medium (36 to 50 mm), and low (51
differences in the texture of cooked rice of to 100 mm). The test is especially useful for
nonwaxy varieties that have the same amylose differentiating samples that have 24 to 30 percent
content. To conduct the test, rice powder (100 amylose. For example, of 38 lines having 24 to
mg at 12 % moisture) is placed into 13 x 100 mm 30 percent amylose with BPI-121-407 as parent culture tubes and wetted with 0.2 ml 95 percent (24 to 26% amylose and low gel consistency), ethanol containing 0.025 percent thymol blue. nine had high consistency, 12 had medium
The tube is shaken to suspend the starch, then consistency, and 17 had low consistency. Aging
2 ml of 0.2 N KOH is added and the mixture is of raw rice has little effect on gel consistency.
dispersed using a Vortex Genie cyclone mixer And, samples of the same variety differing in
(setting of 6). The tubes are covered with glass protein content by as much as 5 percentage marbles and placed for 8 minutes in a vigorously points gave similar gel consistency values. boiling water bath to reflux. The samples are Consistent atypical gel consistency values
removed from the water bath, set at room tem- 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 tR8.
Total protein Albumipn-globulin Lysine content'
Variety Of milled rice Lysine content' Of total protein Lysine content' of residual protein
(%) (g/16.8 g N) M%) (g/16.8 g N) (g/1 6.8 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%): 0.379g/16.89g N.


_141__1. Typical 4.4", pastes of rice with high, medium, and low gel consistency.

of the same variety in three of the varieties tested. U.S.S.R., and U.S.A. Egyptian rice with poor Samples of the same variety also differed widely eating quality (25 % amylose) had high gel in amylograph setback viscosity. consistency. The French variety Arlesienne
Resurvey of world rice. In the early 1960's we (240; amylose) also had high gel consistency. obtained rice samples from rice producing The Italian variety Raffaello (2500 amylose) had countries to check the amylose content of medium gel consistency. varieties. This year we resurveyed the amylose Among tropical rice varieties, low amylose content of world rice after the introduction of prices of good eating quality such as Khao Dawk the semidwarf rice varieties using the more Mali 105 from Thailand and Chhuthana from accurate simplified assay for amylose developed Khmer had low gel consistency. Among tropical in 1971. Amylose content can be classified as prices with an amylose content above 24 percent, low (< 20%), intermediate (20 to 25%), moder- most had a low gel consistency, even those with ately high (25 to 27%), and high (27 to 33 %). Gel above 27 percent amylose. Four out of five consistency values were also determined on these market samples of fine-grain rice in Hongkong samples. (28 to 30% amylose) had low gl consistency and
The amylose contents of the indica and the fifth sample had high consistency. The new japonica rices overlapped (Table 4). The highest Indian variety lET 1991 and the premium South amylose content for a japonica variety was 27 Vietnamese variety Tau Huong had low gel percent for Ponta Rubra from Portugal. Most consistency. Both had high amylose content. japonica varieties, except those from Egypt, Among the IRRI varieties, the gel consistency France, and Italy, gave low gel consistency of IR5 and IR24 was low; of IR26, low to ratings. Hence, amylose content differentiates medium; of 1R20, medium; and of 1R8 and varieties better than gel consistency for rices 1R22, high. The amylose content of IR24 was from Japan, South Korea, Bulgaria, Portugal, low; of IR20 and probably vR26, moderately


high; and of IR5, IR8, and IR22, high. The Arnylogroph setback scosity Brobender its
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- 0
pines at Los Bafios gave highest scores for cooked rices with low gel consistency, followed by those with medium consistency, and then 0
those with high consistency. The check variety C4-63G (25 00 amylose) with a high preference
score also had low gel consistency. The upland varieties Azucena, C22-51, Dinalaga, Man- I I
garez, and Palawan were verified to have 30 40 50 60 70 80 90 100
intermediate amylose content (23 to 25 %). The l-*ih-I*nflidej, Length of gel (mm)
prized aromatic variety Milagrosa had 24 per- 2. Relation of gel consistency (length of 4.4% milled-rice gel
cent amylose and had low gel consistency. in 0.20 N KOH) to amylograph setback viscosity of 9%
The results indicate the applicability of gel paste. consistency in differentiating varieties of similar amylose contents above 24 percent amylose. In intermediate (700 to 74'Q for indica rice (Table
general, low gel consistency is preferred over 4). High gelatinization temperature (>74*C)
medium or high consistency among these rices. was restricted to waxy and low amylose prices.
A notable exception is Basmati-type rice which Mutants differing in grain shape. Workers in
may give medium gel consistency. India have produced mutants of indica and
Final gelatinization temperature was mainly japonica prices differing in grain shape which they
low (<700C) for japonica rice and either low or 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
cuty(no.) (% dry basis) types temperature types
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 LI
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 LI
I= low; M = medium; I =intermediate; H =high.


amylose content from the parent. These mutants degree of milling (Table 5) because parboiling were termed "indica" or "japonica" depending caused thiamine to diffuse inwardly. Both the on the shape of their grain. Because of the poor degree of loss and the degree of diffusion decorrelation between amylose content and grain ended on the severity of heat treatment. This shape, we analyzed a crop of mutants of Tainan inward diffusion was verified by thiamine assay 3, TNI (Taichung Native 1), and IR8 grown at of three successive outer milling fractions and of IRRI. The three "indica" mutants of Tainan 3 the residual grain of raw and parboiled IR22 rice. had 12 to 17 percent amylose while Tainan 3 The bran-polish of parboiled rice had a higher
itself had 19 percent. The three "japonica" fat and protein content than bran-polish of raw mutants of TNl had 28 to 29 percent amylose rice at the same degree of milling (Table 5). The while TNI itself had 28 percent. Similarly IR8 starchy endosperm of parboiled rice has a greathad 29 percent amylose and its four fine-grain er resistance to milling, hence the bran-polish mutants had 28 to 30 percent amylose. The and the germ were more completely removed.
amylograph set-back viscosity of these mutants Milled parboiled rice, however, was not sigwere similar to that of the parent sample. Hence, nificantly lower in protein content than milled the amylose contents of the mutants were similar raw rice. The starch content of bran-polish from to those of the parent varieties, in spite of the parboiled rice was lower than that of bran-polish change in grain shape so it is misleading to call from raw rice. them indica or japonica mutants. We verified that the degree of parboiling and
Parboiling and nutrients of grain. Previous percentage of parboiled grains are measured by a studies (1968) showed that parboiling causes modified alkali test developed by Indian worklittle or no redistribution of protein in the rice ers. Soaking milled rice for 1 hour in 1 percent grain. This year we studied whether water- KOH caused some disintegration in parboiled soluble vitamins such as thiamine (vitamin B,) rice and no swelling in raw rice even for IR22 diffuse into the endosperm during parboiling. which has a low gelatinization temperature. Aside from laboratory samples, parboiled rice Flattened parboiled waxy rice. Five waxy prices samples from U.S.A. and Sri Lanka were ana- from the 1972 wet season crop were studied for lyzed. We found that parboiling decreased the physicochemical properties and suitability for thiamine content of brown rice due to heat making pinipig (a Philippine flattened parboiled degradation (Table 5). The least degradation waxy rice). Storage of the pinipig for a few weeks was shown by samples from hot-sand parboiling amplified sample differences in stickiness of (a method developed by IRRI agricultural pinipig after hydration. The final gelatinization engineers) with a heating time of less than 0.5 temperature of starch granules of Philippine minute. Parboiling for 10 minutes at 121*C waxy lines was either low (<70*C) or high caused greater loss of thiamine than parboiling (74.5*-79*C). Pinipig processors preferred Mafor 20 minutes at 100'C. lagkit Sungsong because as hydrated pinipig it is
Milled parboiled rice, however, contained more tacky or sticky than pinipig from other more thiamine than milled raw rice at the same waxy rice even after storage (Table 6). CoinTable 5. Effect of parboiling method on nutrient content and distribution in brown rice (at 14% moisture).

Treatment Degree of oThiamine (pglg) Protein (%) Bran-polish
milling Brown rice Milled rice Milled rice Bran-polish fat as
Laboratory method (hot soak) (iR20 and p l222)
Raw (check) 11.6 3.80 0.58 9.0 13.4 16.6
Treated brnpls 11.1 3.60 0.95 8.7 13.6 17.4
Treated 121 f no12.0 3.17 2.94 8.6 15.0 19.8
Heated-sand drying (h20 and dree 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
nSi (5%) 0.8 0.39 0.55 0.9 0.5 2.7


pared with the four other rices it had higher and steamed. A consumer panel gave higher
alkali spreading values corresponding to a lower scores to samples that had low gelatinization gelatinization temperature of starch granules. temperature than to those that had high gelatiThe amylopectins differed in molecular size, as nization temperature, but the scores for the
indexed by sedimentation constant, and in mean two types overlapped (Table 7). Measuring
chain length. Using a 9-percent neutral rice gel stickiness using a beam balance technique gave we found that increasing stiffness of the gel similar results. In previous tests freshly boiled
corresponded to a decrease in stickiness of waxy rice gave similar taste panel scores regardhydrated pinipig. Malagkit Sungsong also had a less of gelatinization temperature. But the softhigher level of hot-water soluble starch than the ness of suman which had been stored at 4*C for other samples. several days clearly differentiated samples that
Thus waxy rice suitable for pinipig-making has had high gelatinization temperature from those a low gelatinization temperature and a low gel with low gelatinization temperature, with the
consistency (of 9 0 paste). The relatively low exception of 1R833-6-2. Softness was determined molecular weight of amylopectin in the samples by an improvised penetrometer. Waxy rice with
with low gelatinization temperature probably low gelatinization temperature is preferred for
contributes to the stickier texture and softness of the preparation of waxy rice cake because it has hydrated pinipig. a slower rate of retrogradation or hardening of
Waxy rice cake. Thirteen waxy lines from cooked rice as compared with prices with high
1973 dry-season yield trials of the University of gelatinization temperature. Values for hotthe Philippines at Los Bailos were assessed for water-soluble starch (11.3 to 13.4% glucose)
suitability for suman (a Philippine waxy rice overlapped among the two gelatinization-temcake) by home technologists at UPLB. Three perature classes.
parts milled rice were cooked with five parts The behavior of the IR833-6-2 sample was
coconut milk, then wrapped in banana leaves anomalous because it was one of the better lines

Table 6. Physicochesical properties of waxy prices differing in the quality of hydrated stored pinipig.
Milled rice Starch
Stickiness of Alkali Gel Final Sedimentation
Variety or line hydrated pinipig spreading consistency gel. constant, S
(g/g hydrated pinipig) valued (mm) temp. ( ps)
Malagkit Sunglong 336 6.0 68 61 82
eR833-6-2 192 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. 'Modified 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. 10.5% solution in dimethylsulfoxidle.

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 consistency (mm) score (g/cm ) index (mm)
Four lines high 2.7 0.20 37w 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
TR833-6h2 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

T200 mg rice in 2 ml 0.1 N potassium acetate. Total of 12 assessments per sample. 39judges given four sampleseach with scores between
1.03 to -1.03 (Mrs. A. M. del Mundo, home technology depot. University of the Philippines at Los Bancs). oSample mean.


Peak viscosity ( Brabender units protein content on these properties was not
1200 clear-cut.
During steaming, however, waxy and low
1100 -amylose prices were not able to retain the enIR22 trapped gas (GO2) while rice with 24 to 26
IR24percent amylose (C4-63G, Intan, BPI-76-) 1000showed adequate gas retention resulting in good 1R833 volume expansion. Intermediate amylose content also insured a soft texture for the steamed
900cake. These prices also had low gel consistency, IR480except for R20 which had medium gel consistency.
800Mechanism of rice aging. Most studies on the changes rice undergoes during storage have been
made with milled rice although rough rice and
700brown rice are known to undergo the same changes during storage. To obtain a general
mechanism of rice aging, rough rice, milled rice,
600surface-defatted milled rice, and rice starch of
0 2 4 6 four samples with 0, 19, 24, or 29 percent
Months of storage amylose from the 1972 dry season crop were
3. Effect of storage on amylograph peak viscosity of 9%
starch paste of four rices differing in amylose content. differing in protein content were also included. IR833-6-2 milled rice is waxy, IR24 has 18% amylose, Ingeneral, all samples showed similarchanges IR480-5-9 has 24% amylose, and IR22 has 29% amylose. regardless of the form of storage, amylose content, or protein content. Most notable was
for pinipig preparation. But the low preference the increase in amylograph peak viscosity rescores coincided with its poor stickiness index. gardless of amylose and protein contents (fig. 3 With IR833-6-2 excluded (n = 12), the cor- and 4). Denaturation of the a-amylase of brown relation coefficient with softness was 0.92** for rice flour by acidification and subsequent neualkali spreading and 0.92** for gel consistency. realization did not result in an increase in The corresponding values with IR833-6-2 in- amylograph peak viscosity of freshly harvested cluded (n = 13) were 0.78** and 0.83**. rice. Volume expansion and water uptake during
Fermented nonwaxy rice cake. Rice varieties cooking increased while dissolved solids desuitable for making fermented nonwaxy rice creased progressively, particularly in samples cake (puto) produce dough which retains gas stored at 28*C. Hardness values (as indexed by adequately during yeast fermentation and give percentage of powder coarser than 80 mesh after steamed cake with good texture. C4-63G is the grinding 20 seconds in a Wig-L-Bug amalgavariety manufacturers prefer. Among 10 rices mator) increased with aging. They were higher aged for a year prior to milling, gas retention for the high protein sample of each rice. Free during fermentation of the dough tended to fatty acids were highest in milled rice stored at decrease with increasing amylose content and 28'C compared with defatted milled rice at 28'C was higher for waxy rice. In addition, relative and control samples at 4*C. No trend was found viscosity of the dough using a pipette also was for in vitro digestibility of cooked rice with anegatively correlated with amylose content, amylase, amylose, and protein content, and in indicating cohesion between raw starch granules. the gelatinization temperature of starch. StickiSince rice dough, unlike wheat, has no gluten, gas ness measured by the beam balance technique retention during fermentation is probably due to showed no change in value for cooked waxy rice cohesion of starch granules in the dough as but showed significant decreases for the 19 and affected by amylose content. The effect of 24 percent amylose samples. The technique was


Peak viscosity ( Brabender units) of essential fatty acids (mainly linoleic) than
900 bran-polish oil. Since later studies elsewhere
showed the opposite relationship using chloro800 form/methanol (2/1 vol/vol) instead of petroLowleum ether, we restudied, by gas chromatoLow roten, soredgraphy, the fatty acid composition of oil extracted from bran-polish and milled rice of IR20 and
700 .
Low protein R22. Methyl esters were prepared by refluxing
no storage
oil in methanolic HC1.
60High protein, stored --The fatty acid composition of oils extracted from bran-polish and milled rice with petroleum
00.001.01ether were similar and the ratios of oleic acid to 500linoleic acid were about 1.0 (Table 8). Milled High protein, no storage rice oil extracted with methanol/chloroform, however, contained more linoleic acid and less
400oleicacid than oil extracted with petroleum ether.
0 1 1 1 1 1 1Thus, oil extracted by the polar solvent meth0 5 10 15 20 25 anol/chloroform was more unsaturated than
Amytose content (%/ dry basis)
Annyoseconent % dy bsisneutral oils extracted with petroleum ether.
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. SEED AND PLANT METABOLISM

Oxygen uptake, peroxidase, and grain dormancy.
not sensitive enough for flaky rice (2900 Studies last year indicated rice hulls have a high amylose). peroxidase activity and that dehulling increases
All the major fractions underwent changes germination of dormant grain. But oxygen
during aging. The solubility of starch in hot uptake, measured by Warburg manometry, did water decreased. Since high protein samples and not show a corresponding increase after desurface-defatted samples behaved similarly to hulling. Changes in oxygen uptake, peroxidase milled rice, and since starch also showed similar activity, and dormancy were examined during amylograph changes to those in milled rice, the the development of the grain (variety H4) in the starch fraction probably contributed more to 1973 wet season. Ripening grains were assayed the changes during aging than protein and fat, with and without air-drying. We measured
Composition of rice oils. Ten years ago we oxygen uptake by a polarographic assay with found that oil from milled rice has lower iodine the Clark oxygen electrode on grains which had value (is more saturated) and smaller amounts 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 R22 extracted with petroleum ether or methanol/chloroform.
Composition' (%)

Fatty acid Bran-polish oil Milled rice oil
pet. ether pet. ether methanol/chloroaorm LSD
nR20 sR22 IR20 R22 R20 R22 (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.


whole grain decreased progressively during dwarf varieties are less suitable for parboiling ripening. The dehulled fresh grain (brown rice) than grains of traditional rice varieties due to had 4 to 29 times higher rates of oxygen uptake greater dry matter loss during soaking. In than the whole grain and dehulled air-dried addition, the breakdown products act as subgrain had four to six times higher rates partic- state for microbial growth in the steeping ularly during the first 2 weeks of grain develop- water. Since the new varieties have weaker ment. Peak uptake for dehulled grain occurred dormancy and different starch properties (parabout 10 days after flowering (623 nmol/h 02) ticularly gelatinization temperature) than the
Germination of dehulled air-dried developing traditional varieties, we studied the rate of grain was nil in the 4-day grain (i.e., 4 days after release of free sugars and dry matter loss of flowering), 45 percent in the 7-day grain, 67 varieties differing in gelatinization temperature, percent in the 10-day grain, and 87 percent in presence of white belly, and amylose content at the ripe grain. Fresh grain failed to germinate. different degrees ofdormancyduring soaking for Peroxidase activity was constant during the I to 4 days in water at 30*C. first 3 weeks of grain development (1.2 to 1.4 Dormancy and endosperm opacity contribnmol purpurogallin min- seed- 1) but de- uted to differences in dry matter loss. Dormant creased during grain desiccation (to 0.22 nmol samples released sugar in the soaking water purpurogallin). The hull contributed from 80 to more slowly. In addition because another 90 percent of peroxidase activity of rough rice. contributing factor was their characteristic The results are consistent with the reported white belly, 1R8 and IR5 rice gave higher free viability and complete formation of the embryo sugar formation after 1 day of soaking than a I week after flowering. waxy rice sample. Presumably, the air spaces
A comparison of dormancy and 02 uptake of between starch granules in the white-belly ripe H4 seeds showed that the oxygen uptake of portion of IR8 and IR5 allow faster dry matter fresh rough rice (0% germination) was 8 nmol/h, loss than the air spaces in the starch granules of that of air-dried rough rice (1.3% germination) waxy rice. Nondormant IR22 grains with transwas 12 nmol/h, that of fresh brown rice plus hull lucent endosperm and low gelatinization tem(780% germination) was 34 nmol/h, and that of perature had similar rates of dry matter loss to air-dried dehulled rice plus hull (87% germin- nondormant H4 with intermediate gelatinization ation) was 53 nmol/h. Apparently the hulls of temperature. That indicates that gelatinization dormant grain are a barrier to oxygen uptake by temperature of starch is a minor factor in dry the rice seed thus retarding germination. Oxygen matter loss during soaking. uptake by nondormant rough or brown rice Enzyme changes during germination. We
increased progressively during the first 6 hours studied the endosperm enzymes, catalase and of soaking. cellulase, for changes in germinating IR8 grain.
Pricking brown rice at the distal end before Catalase levels increased progressively during soaking in water for 20 hours did not increase germination in light and reached a maximum oxygen uptake (42 nmol/h), but pricking at the (15 times that of the mature grain) on the sixth embryo end increased oxygen uptake to 56 day of germination. The changes followed a nmol/h. No difference occurred in seeds soaked trend similar to those of peroxidase. Cellulose for 2 hours. Since pricking brown rice near the activity, measured by release of reducing sugars embryo results in complete germination, the from carboxymethyl cellulose, showed a first aleurone layer and seedcoat, as well as the hull, peak on the third day of germination followed reduce the oxygen uptake of the embryo. Thus by a decrease during the fourth to the sixth day the apparent dormancy of the rice grain is not and an increase again in activity on the seventh seed dormancy, rather the covering structure of day. the nondormant embryo restricts oxygen dif- The sequence of production of phytase, lipase, fusion, thus preventing germination. and fl-l,3-glucanase was studied in embryo-less
Dry matter loss during grain soaking. Indian IR8 seed halves incubated in 0.2 PM gibberellin workers have reported that grains of the semi- A3. In germinating rR8 grains, they are pro10 IRRI ANNUAL REPORT FOR 1973

duced in the endosperm in the order: phytase, the aleurone layer were probably more damaged lipase, fi-glucanase. In the embryo-less seed during milling than those of the germ. halves, phytase was produced first, followed by Starch synthetase of grain. Starch synthetase fl-glucanase and lipase together. Lipase produc- is the key enzyme involved in converting tion was delayed and its activity was slower in nucleotide glucose derivatives into amylose. It this artificial medium. Phytase activity was lower is present mainly in a form bound to the starch but that of fl-glucanase was higher. Delayed granule in nonwaxy rice, but a soluble fraction is lipase production has been also reported in also found in developing rice grains. Previous wheat seed halves. Glutamine and hydroxyla- attempts to make the bound synthetase soluble mine (1 mM) which accelerated lipase production had limited success. in wheat had no effect on rice lipase production. In cooperation with Dr. E. J. del Rosario of Production of fl-glucanase coincided with pro- University of the Philippines at Los Baflos duction of -amylase in the embryo-less seed chemistry department, we isolated starch granhalves in gibberellin A3. Thus hydrolases in the rules from developing IR8 grains at the midmilky rice aleurone layer were produced in sequence stage and purified them by repeated washing during germination and during incubation in with water, and then with 0.1 M phosphate gibberellin A3. buffer (pH 7.2) containing 0.006 M magnesium
RNase (ribonuclease) is a key enzyme of chloride. The washed starch had 2.0 percent nucleic acid metabolism in developing and protein. The granules were made amorphous by germinating grain. RNase I or cytoplasmic placing 200-mg lots in a Wig-L-Bug amalgaRNase is found in large amounts in developing mator for 30 seconds.The granules were dispersed and mature corn. In a study on RNase I in using ultrasonic vibration at 20 kHz for 1 hour degermed IR480-5-9 grain, the highest activity in 0.05 M HEPES (pH 7.5) containing 75 percent was in a sample germinated 4 days in the dark dimethylsulfoxide and 0.001 M dithiothreitol, (46 AA260 30 min-' grain-'), followed by and then centrifuge. About half of the residual developing grain at midmilky stage (17 AA260' protein of the starch granules was dispersed by 30 min-' grain-') and least in the mature this treatment and it had a specific activity for grain (3AA 260 30 min-' grain '). Disc starch synthetase essentially the same as that of electrophoresis indicated the presence of one the washed granules. In the precipitate collected major fast-migrating, distinct, and very active by trichioroacetic acid addition to the protein RNase isozyme band in the endosperm of extract, the ratio of carbohydrate to protein
developing and germinating grain. The RNase was 5.5. isozyme was not distinct in the mature grain In a discontinuous sucrose-density-gradient although a corresponding protein band was centrifugation of the solubilized enzyme, two present in the extract. The major RNase band opaque bands were present between 35 and 45 was identical in both germinating and develop- percent sucrose and between 45 and 55 percent ing grain: the band had the same width in a sucrose. The lighter band corresponded to peaks mixture of the two extracts. Two minor, slower in protein content and starch synthetase activity migrating RNase bands were present in the in the absence of added glycogen primer. This developing grain but absent in the other samples. band was also the fraction with highest amyloseLipase production in bran. The foregoing iodine blue color. The heavier protein band had results on rice seed halves incubated in gibber- no synthetase activity even in the presence of ellin A3 indicated a delayed production of lipase primer. The results indicate that the lighter compared with the germinating seed. Since fat enzyme fraction is tightly completed with hydrolysis by lipase is the major reason for the amylose which functions as primer for the poor keeping quality of rice bran, the nature of synthetase assay. lipase production in rice bran was examined. Disc electrophoresis of the solubilized enzyme Preliminary studies indicated that the aleurone had three bands which stained for both protein layer produced free fatty acids at least three and carbohydrate. Two other faint bands were times faster than the germ fraction. The cells of obtained. The band of slowest mobility showed


the most intense staining. glutamate dehydrogenase activity was at least
Seedling test for grain protein content. In as high as in control plants.
studies elsewhere on corn and wheat, the highest Leaf proteins. A study was made of the proactivity of nitrate reductase occurred in 1-week- tease and fraction I protein of rice leaf blades. old seedlings and correlated with grain protein Protease was extracted from active (second) leaf content. Since our previous studies with 2.5- blades with 0.1 M phosphate buffer (pH 7) with week-old seedlings showed no relationship 5 mM glutathione. Its activity was highest in the between grain protein and seedling protein protein fraction that precipitates from solution levels, we studied this relationship in younger between 60 to 80 percent saturation with ammoseedlings grown in Hoagland's solution contain- nium sulfate. Optimum pH was 7.0. Disc electroing 40 ppm of either ammonium or nitrate nitro- phoresis of the fraction indicated that protease gen. Low and high protein seeds of IR8 and corresponds to protein bands of intermediate IR480-5-9 were used. We found greater differ- to high mobilities. No difference in electroences and higher nitrogen levels in 1-week-old phoretic pattern was noted in the protein seedlings than in 2-week-old ones. The total isolated from plants at maximum tillering, protein of the active leaf (topmost fully expanded panicle initiation, and booting stages. leaf) was higher in IR480-5-9 than in IR8 due to a Fraction I protein constitutes 45 to 50 percent heavier leaf and a somewhat higher protein level. of the soluble chloroplastic protein of vascular The difference in protein level and weight of total plants. It contains the central enzyme in phototops was not significant. The high protein synthetic CO2 fixation of the rice plant-ribulose samples of the two rices tended to have lower dry 1,5-diphosphate (RuDP) carboxylase. Workers matter production. Better foliage growth occur- elsewhere have been able to crystallize fraction I red in the ammonium medium than in nitrate, protein from tobacco leaves by dialysis against and leaf protein levels were higher. Levels of water. We tried such a procedure on IR20 leaf leaf nitrate reductase and root glutamate dehy- blades. Ammonium sulfate fractionation showed drogenase were not related to grain protein that the fraction precipitating between 20 to 40 content. percent saturation with ammonium sulfate had
Repetition of the screening using 21 promising 56 percent higher RuDP carboxylase activity high protein lines did not reveal a trend between than the crude extract. Disc electrophoresis foliar nitrogen and grain nitrogen. Hence showed that fraction I protein contains two seedling vigor was not simply related to grain major bands. Loss of RuDP carboxylase activity protein content and the trend found for IR8 and of fraction I protein after freeze-drying the fresh IR480-5-9 was due mainly to lower weight.of the leaf blades was associated with the loss of the active leaf and tops of IR8. slower migrating band. Storage of the crude
We also found that 1-propanol (5%) gave extract for more than 4 days at -20*C also higher values than two commercial surfactants caused this slower migrating band to precipitate. as wetting agent in the in vivo assay for nitrate The ammonium sulfate fraction was desalted reductase in segments of rice leaf blades. in Sephadex G-25, concentrated by treatment
Effect of herbicides on seedlings. Two weeks with polyethylene glycol, and induced to crysafter flooded soil in which 2.5-week-old IR22 tallize by dialysis against dilute buffer. No seedlings were growing was treated with 0.075- crystals formed from fraction I protein of rice ppm simetryne or 0.15 ppm benzomarc, the indicating that it is albumin-like, in contrast
leaves of the plants had higher total dry matter with fraction I protein of tobacco which is but the same nitrogen level as leaves of the un- globulin-like and hence becomes insoluble and treated control. In addition, levels of chlorophyll crystallizes out as salt concentration decreases and free amino acids were higher in leaves of the slowly during dialysis. treated plants. The glutamate dehydrogenase Resistance to brown planthopper. Studies with activity was lower in roots of treated plants due IRRI entomologists on the isolation of a to the lower level of soluble protein since specific chemical factor in rice plants for resistance to the


brown planthopper (Nilaparvata lugens) were blade dropped from 76 percent to 62 percent continued. Attempts to air-dry plants on large during 5 days infestation, as measured by the scale caused a large decrease in recovery of the #-gauging method. The amount of honeydew factor compared with extraction from fresh collected daily from the feeding insects and its tissues. Methanol (50%) extracts of Mudgo x content of sugars and amino acids were variable. IR8 plants continued to show higher activity on Total amino acid, particularly proline level, was brown planthoppers than extracts of IR8. Hot higher in leaf blades of infested plants than in extraction gave higher recoveries than cold leave blades of control plants. Nondestructive extraction, but the difference in activity between methods--gauging, leaf diffusive resistance, IR8 and Mudgo x IR8 extracts was reduced. and leaf temperature-were less sensitive than
Hopperburn. Further studies were made with chemical measures such as proline content for IRRI entomologists on the changes in leaf blades indicating stress in the plants. Leaf blades of and sheaths which occur during brown plant- rice plants subjected to water stress by IRRI hopper infestation, using Taichung Native 1 agronomists have also shown higher proline seedlings. In experiments using nondestructive content. methods, the moisture content of the active leaf


M u ltip le The cropping systems program is
using the resource utilization apc ro p p mn g roach 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. O 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 arrangement. 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 difficultto-control grasses and sedges with intensified cropping. The control of crop leaf area index coupled with proper management techniques has potential for this control. l 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 with natural rainfall and with irrigation, in a low
We are developing improved and intensified p
cropping patterns to increase the welfare of rice these practices by small farmers (throughout the farmers in Southeast Asia. Cropping systems tropics) leads us to wonder about their efficiency technology is being organized to use farmers' in meeting their needs. The often-used practice resources more efficiently in meeting this goal. of intercropping has been chosen for study under resurpec pngown more efficientl our resource utilization model. Its biological
Multiple cropping-growing more than one
cropon he sme iec of andin yea-istheas well as resource-use characteristics have been crop on the same piece of land in 1 year-is the eautd most common method.
A small, or "disadvantaged," or "poor" Types of intercropping. We have investigated farmer, typified by the average Asian rice farmer, two types of annual-crop intercropping patterns.
sell ony a mal shae o wha heprodcesThe first, which is most widely used by farmers, sells only a small share of what he producesinldsatl-rwg(omat)cpada because his land holding is too small, because he lacks other production resources, or because he shor statured second oina lacks technology, or, more often, a combination tion also has a dominant and a secondary crop, of the three may apply. with the secondary crop being harvested either
We are striving to develop technologies at the same time as the dominant crop or earlier adapted to specific farm types, which are grouped by the degree to which a farmer (fig. 1)i participates in a market economy as well as by odectioi Toal procyiatbas his physical resources. Based on yields from several replicated trials,
crop combination can increase land productivity LESSONS FROM TRADITIONAL from 30 percent to 60 percent over monoculture
TECHNOLOGY cropping (Table 1). The land equivalent ratio
In the process of developing cropping systems (LER) is the total land required using monotecholoy fo th "smll"farmr w exaineculture to give total production of the same crops technology for the "small" farmer we examine his current cropping practices to see if clues can equal to that of I hectare of intercrop. It is
be fundas t ho hi lotmaybe mproed.Thecalculated by determining the ratio of the yield of be found as to how his lot may be improved. Theacrpiamxtetotsyldnmncuue Javanese small farmer serves as our model. We ancr in am e togit ieds monocltr find him using labor-intensive methods to grow er the sae mgmn cuue frity several field crops in various combinations, both ratios of all
crops in the mixture are then added to give the A. Dominant crop harvested first land equivalent. For example in a corn-soybean

Corn intercrop (Table 2), corn yielded 5.28 t/ha and
the soybeans yielded 0.85 t/ha. The monoculture Peanut, sweet yields (at optimum populations, but at the same
potato or rice ,~management level) were 5.52 t/ha for corn and
2.33 t/ha for soybeans. The ratios of intercrop B Dominant crop harvested lost yields to monoculture yields were 0.96 for corn and 0.36 for soybeans. The sum is 1.32. Total Corn productivity is thus 32 percent higher, and the
Mung orland equivalent is 1.32 hectares.
soybeans These results indicate that during the dry
season under irrigation, intercropping (alternaterow planting) is usually more productive than
0 1 2 3 4 monoculture.
Months Wet season rainede) trials in a farmer's field
1. Common types of interoropping patterns showed similar results from corn-rice inter16 IRRI ANNUAL REPORT FOR 1973

Table 1. Land equivalent ratio (LER) under good man- cornpopulation. Wehaveplottedcornandmung agement for five crop combinations with corn (95-day yields as a fraction of their monoculture checks maturity). IRRI, 1973 dry season. (at the same management level) for several levels
Crop Maturity (days) LER of weed control andfertility in figure 2. Points
Dry soybeans' 90 1.3 on a curve represent differences in corn populaGreen soybeans0 65 1.6 tons only. As corn population increases, its
Mung bean' 60 1.5
Sweet potato 120 1.5
Peanutb 110 1.6 linear fashion (as shown by the high r values).
*From a single management level, four replications. bAvg of
four levels of weed management, three nitrogen levels, and urges show the relative increase in productivity eight corn populations and row spacings. over the monoculture check (lines of equal
LER). At 270 kg/ha of nitrogen and with weed
Table2. Effectof intercropping field corn' insoybeans.b control (1.5 kg/ha a.i. of butachlor) the advanIRRI, 1973 dry season. stage of intercropping remained 20 to 30 percent

Crop Grain yield' (t/ha) above monoculture. Only with no weed control
combination Corn Soybean LER
Soybean alone 2.33 Table 3. Yield and gross returns from upland rice-corn
Field corn alone 5.52 intercropping. Farmer's field. Laguna, Philippines. 1973
Soybean + field cornd 5.28 0.85 1.32 wet season.
'Variety Thai Early Composite (87-day maturity). bVariety Yield' Value
Multivar 80 (85-day maturity). CMeans of four replications. (t/ha) (P/ha)
dl -m spacing.
Corn (Thai Early Composite) 4.3 4300
Rice (fR442-2-58) 3.9 3100
cropping (Tables 3 and 4). IRRI trials of Corn and 4.0
rice 2.2 5800
intercropping patterns have thus shown that Corn (Penjalinan) 1.7 1710
under Los Bafios conditions, with highly pro- Rice (IR442-2-58) 3.8 3055
ductive improved varieties having approximately Corn and 1.4
the same growth duration as farmer's varieties,
intercropping makes better use of a farmer's At the best management level.
land resources. A higher return on cash inputs
may even be possible (Table 5). Table 4. Corn (Early Thai Composite. 85-day maturity)
Plant spacing and time of planting. The timing and rice (IR442-2-58. 120-day maturity) intercropped
of the overlap period and the crop configuration at varying levels of nitrogen. Farmer's field. Laguna,
(row spacing, population) are important to the 1973 wet season (avg of four replications.
successof these patterns. In ourtrials, both crops Crop Yield (t/ha) Total value
in the combinations were planted at the same Rice Corn (P/ha)'
time. With corn-mung, the mung reaches the 60 kg/ha N
flowering stage (30 to 35 days after planting) Corn 3.9 3900
before being shaded by corn. The yield reduction Rice 4.2 3300
Rice and corn 1.5 2.9 4100
in the mung (as compared with monoculture) is 120 kg/ha N
usually about 50 percent if nothing hinders the Corn 4.0 4000
mung growth relative to that of corn. If mung is Rice 4.4 3500
Rice and corn 2.2 2.8 4600
planted after corn it will not yield well because of 180 kg/ha N
its sensitivity to shading in the seedling stage. Corn 4.3 4300
Since mung usually covers the ground rapidly it Rice 3.9 3100
would not be effective to plant corn later because 240 kgh N
the corn is equally sensitive to shading in the Corn 4.4 4400
seedling stage. Rice 3.0 2400
The total productivity of corn-mung when Rice and corn 2.0 3.4 4900
planted together is rather independent of the P804/ of rice, P1 000/t of corn.


Corn yield in intercropping as a fraction of Table 5. Peso return per peso of added nitrogen in
its monoculture check corn-rice intercropping. Farmer's field, Laguna, 1973
N $* wet season (avg of four replications).
1 No weed control, 180 kg/ha N
\, (r=-0984*) and 270 kg/ha N Return (P/ P added nitrogen)
1.6 (r=-0.997*) Nitrogen increment
.4(kg/ha) Rice alone Corn alone Intercrop
%%60-120 2.2 1.1 5.6
Weed control, 180 kg /ho N 120-180 -4.4 3.3 13.3
%% r-9*)180-240 -7.8 1.1 -10.0
1.2 % Weed control, 70 kg /ha N
1.2 ( r = -0.953*)
r -0-953The normal crop configuration used by farmers, when mixing crops, is to plant a solid stand (as in monoculture) of the low-statured "minor"~ 0.8 -crop and then introduce the major crop at vary0.8
ing populations and row spacings. We have followed this practice in the intercrops of corn Weed control with mung, soybean, peanut, sweet potato, or
270d kg/hao N 60* rice. Although the time of planting should be the
270 kg/ho N
0.4 (r=-0.978*) same for corn and mung, with corn-soybean, the
soybeans start more slowly and a delay in the
+ 40%
+4% planting of corn seems beneficial (fig. 3). When + 0% DMR-2 corn was planted 20 days after soybeans
(Shih Shih) and the soybeans were harvested as a 0 green vegetable, the productivity of the combina0 0.2 0.4 0.6 0.8 10 1.2
Mung yield in intercropping as a fraction of its monoculture check tion was 102 percent higher than that of either 2. Relations between the yields of corn and mung in an crop alone and 80 percent higher when harvested intercrop combination as a result of different corn row dry as shown by LER values of 2.02 and 1.8 spacings and populations at three levels of nitrogen and two respectively (fig. 3). The 20-day delay allowed the levels of weed control. IRRI, 1973 dry season, soybeans to get a start before being shaded by
the faster growing corn.
and high nitrogen levels was there a marked Physiology of intercropping. When the growing
increase in productivity with increasing corn and reproductive stages of both crops coincide,
population. Although the relative advantage of as with combinations such as corn-mung and
intercropping is greater under low management corn-soybeans, and when the populations of
than it is at high management (100% vs. 30 to both crops are high, the relationship between
40 %) the actual productivity may be lower the yields of the two crops is linear at a nearly
(Table 6). constant level of productivity for a given manTable 6. Return per hectare for corn-mung intercropping averaged over corn-plant populations (after deducting the cost of nitrogen). IRRI. 1973 dry season.

Retunb (P(/ha)
Crop( 70 kg/haaN 180 kg/ha N 270 kg/ha N

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

acorn variety, DMR2 (97-day maturity). Mung variety MG50-1 OA (65-day maturity). bCorn = P0.79/kg. Mung = P2.25/kg. cButa. chsor at 1.5 kg/ha a.i.


Fraction of monoculture check Corn yield as a fraction of
its monoculture check
1.2 Dry soybean .0

Green soybeanR1.2
LER .27
LER 1.0

0.4 Corn with dry

0 I IJ I 0.4
Soybean LER

Soben 80 6 40 20 0 I
I/0 0.2 0.4 0.6 0.8 1.0
Mung yield as a fraction of its monoculture check
1. dry
4. Relations between yields of sweet corn and mung in intercrop combinations under different corn populations (with mung population remaining constant). IRRI, 1973
1.0 dry season.
Soybeans t0 60 40 20 0
alone closely when the growing periods have less over3. Effect of time of delay of corn planting in corn-soybean Thesi coric-sswet isofarticula intres intercrop. IRRI, 1973 dry season. checks
because of its widespread use. Two experiments were conducted to study its crop-interrelationageient level. In other words, productivity is ship effects. The Indonesian corn variety Penmaximized at that level of light, water, nutrients, jalinan (70-day maturity to dry corn) was used and other resources in the experiment for that with IR442-2-58 rice. These varieties fit the given crop combination. Sweet corn-mung at usual maturity pattern for this combination in
high fertility with complete weed control illus- farmer's fields. The two crops are planted totrates the principle. As the corn population is gether and the corn is mature just before the rice changed, the relationship between corn and flowers. The rice is not appreciably shaded by the
mung yield is linear at a productivity level 27 corn until about the maximum tillering stage so percent above that of the monoculture checks the period of maximum competition occurs
(fig. 4). A static and an "unsaturated" produc- during the time when rice is least sensitive to tivity are both illustrated by the corn-soybean shading. interrelationship (fig. 5). When planted at the In the first experiment the area in rice was 43
same time, the productivity was 40 percent above percent, 71 percent, or 100 percent (solid plantmonoculture. Corn was favored at 1-meter row ing of rice with corn added in addition) with each
spacing of the corn; the balance shifted towards of three corn populations and two row spacings. soybeans at the 2-meter row spacing with pro- At most corn populations and row spacings, a ductivity remaining constant. A 20-day delay in larger rice area increased total productivity corn planting resulted in a new relationship with without a corresponding decrease in corn yield an 80-percent increase in productivity. (fig. 7). This indicated that the system was not
The relationships do not seem to hold as saturated (at its maximum total productivity


Corn yield as a fraction of level) except at the 43,000-corn population at
its monoculture check 1.4-r row spacing. The absolute productivity at

saturation obviously depends on the productive 1.0 +25% +50% + 75% +100% capacity of the varieties. Table 3 shows the yield
Plate tgehe range for Penjalinan in rice as compared with
Planted together
(I-rn corn row spacing) that of Thai Early Composite. The total pro08 -ductivity of the two different combinations was 20- day delay about the same but was arrived at in different Planted together ways. The productivity of Penjalinan was low,
0.6 (2-rn corn row spacing) but the rice compensated for it. This shortstatured corn variety detracted little from the rice yield; every kilogram of corn yield was a 0.4- bonus. With Thai Composite the rice yield
0 decreased more but the corn was higher yielding.
40-daydelay In another experiment the area in corn and
0.2 -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 00 .6 08 10 1 alternating with 3 rows of corn, 9 rows rice with
02 rows corn, 5 rows rice with 1 row corn, or
Soybean yield as a fraction of its monocature check rows rice with 1 row corn (in this arrangement 5. Effect of intercropping corn and soybeans with different the corn was at equidistant spacing). The objeclength of delays in corn planting after soybeans were planted. tive was to test the hypothesis that the advantage IRRI, 1973 dry season. of intercropping (in a compatible combination)

is derived from achieving maximum contact Corn yield as a fraction of between species. In our experiment the contact
its monoculture check between seiswas maximized witheqistn
16 spce eqiitn

.4 Corn yield as a fraction of
its monoculture check
+40r =0-04669ns 1.0
1.2 +4%+20% +40% +600/
+20% 0.8

l l p aCorn pon. Area
0.4 plant/hal (/)in rice
0.4tf h4,000 E o
0.4- 020,000 V V V
43,000 0 03
02c- Corn spacing
0.2 -1.4m

0 0.0 .r
0 02 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0
Sweet potato yield as a traction of its moraculture check Rice yield as a fraction of its m ionojuure 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.


Table 7. Effect of row arrangement on the gross return Corn yield as a fraction of from corn-rice intercropping with each crop occupying its manocuture check 50 percent of the area. IRRI, 1973 wet season. .2
+20 +40 +60 +80
( 2rs x 0
Return' (P/ha) (2rx Ic) Qs

Crop Row Corn population (plants/ha) 1.0
15,000 60,000

Corn alone Solid stand 710 1400
Rice alone Solid stand 2380 2380 .8
3 x 3b, 15 rice x 3 corn 1560 1580 (5rxlc)
2 x 2c 9 rice x 2 corn 1540 1940 C p
1 X 1e 5 rice x 1 corn 2160 3080 60,000/ha
x d 2 rice x 1 corn 3590 3160

aCorn at M1.00/kg. Rice at P0.80/kg. bThree beds of rice alternated with three beds of corn. cl.4-m row spacing for (9r x 2c Cor pop.
corn. do.7-m rows for corn. .4

corn spacing (two rows of rice with one row of 05r (
corn) at the low corn population. .2 9rs2c I r ( sc
Productivity increased with increasing contact between the corn and rice (fig. 8). The 80-percent gain in productivity when half of the area was 0 1 1
covered with rice, and corn was planted at 15,0000 plants/ha (when compared with solid corn at Rice yield as a fraction of its monoculture check
plats/a (hencomare wih slidcor at 8. Effect of row arrangement on productivity of corn-rice
60,000 plants/ha and a full stand of rice) was intercropwitheachcropplantedto50"%ofthearea(r= rows
surprising. It is evident that in corn-rice, the .of rice, c = rows of corn). IRRI, 1973 wet season. timing of the overlap of these varieties seems to be optimum, but we did not expect that the light interception. Intercropped combinations
increasing contact between species would show usually have a higher total light interception
such dramatic results. The gross return from (Table 8) as well as a more efficient pattern over
these yields confirms the trend (Table 7). the entire season. They thus appear to make
Light interception. At least part of the differ- better use of light resources.
ences in performance between monoculture and Weed response. Light interception also partiintercropping can be explained by differences in ally explains the differences in weed response

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

Crop Corn Corn-row a ra n of
population spacing Above lower canopy Ground level
(103 plants/ha) (in) 44 D5" 63 DS 30 DS 44 0S 63 IDS

Corn 40 1 52 32 26
Corn 20 2 77 57 45
Peanut 60 21 9
Mung -- 49 12 23
Sweetpotato 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

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


seen in intercrop plantings. Mung bean by itself Table 9. Gross returns for corn, mung. and corn-mung is less responsive to weed control than corn alone intercrop averaged over corn populations and nitrogen (Table 9). The corn-mung intercrop has little levels. IRRI. 1973 dry season.
response to weed control because the mung sup- Gross return (P/ha) Increase
presses the weeds, and the total productivity is No weed Weed M
higher. The ability of mung to compete with control control'
weeds, however, depends both on the growing Corn' alone 1300 2450 88
conditions and the type of weeds. Wet weather MUngb alone 2480 2930 18
and low light intensities reduce early mung growth and favor growth of weeds. In the dry P0.79/kg. bP2.25/kg. cButachlor at 1.5 kg/ha a.i.
season with high light intensities and a predominance of annual grasses and sedges which Corn borer infestation normally begins with
are shade-sensitive, the effect of mung on weeds egg-laying moths which select fields by, perhaps, is dramatic. This plant-weed competition, how- the sight and smell of host plants. To examine the
ever, is markedly influenced not only by the type effect of visual stimuli, we placed brown or green of crops in the combination, but by fertility level. burlap between rows in corn plots. We found that
The actual weed response interaction with the moths preferred corn plots with green intercrop and nitrogen level is shown in figure 9. row cover less than those with brown inter-row
Weed yields did not increase significantly under combination with nitrogen level are also importcorn as nitrogen level increased. The increase ant for weed control (fig. 10). Gross returns are
with mung was slight, but peanut failed to sup- always higher from intercrop combinations but press weeds at high fertility levels. Within crop the returns from weed control depend both on combinations a higher population still lowers the population of corn and the nitrogen level.
weed growth(Table 10). The interactions of crop Traditional crop combinations thus have
definite weed competition properties, partly resulting from their light interception patterns. Dry weed wt (t/ho) Crop combinations and insect interactions.
Z Earlier IRRI findings that the traditional interTl9cropping of peanut with corn decreased corn borer infestation have led to more detailed LO 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 popula24 Z tion performance were examined: adult oviposition behavior, larval feeding and establishment on corn, its principal host plant, and effects and interactions of predation by spiders (Lycosa

1.6 spp.) and insecticidal treatments.
z .2 Z
Z Table 10. The effect of corn population and spacing on
weed growth for different intercrop combinations at intermediate nitrogen. IRRI. 1973 dry season.
0a8 f orn w Con rol ( 1 Dry weedwt(t/ha)in
population spacing Mung Sweet potato Peanutb (10t plants/ha) (f) + corn + corn + corn
Ex10 1 1.3 1.8
60 1 0.8 0.6 0.5
010 2 0.5 1.6 1.5
Corn Peanut Corn + Maig corn-I- 20 2 0.3 0.7 1.0
Peanut Mung
9. Interaction effects of crop combination, weed control, Sweet potato alone. 1.8 t/ha of weeds. bPeanut alone. 2.7 and fertilizer level on weed weight. IRRI, 1973 dry season. t/ha of weeds.


Gross return (P/ha) Table 11. Influence of green and brown visual cues on
5000 opposition preference of the corn borer (based on
Cornexamination of 50 plant samples avg of two repli(with weed control) nations). IRRI June-September.1973.
Corn +Mung
400-- (noweedcontrol)
4000(noweedconrolBorer egg masses on corn
Color of inter-row (no.11 00 plants) Decrease
(with weed control burlap cover Corn alone Corn with
3000 peanut
29 days after seeding
None 13 6 54
2000Brown 14 5 64
(no weed control) Brown and green strips 11 6 45
Green 8 6 25
Comn 35 days after seeding
1000None 16 2 88
Brown 46 21 54
Brown and green strips 27 22 19
Green 27 19 30
0 I I I
100 200 300 400 500 42 days after seeding
Nitrogen level (index) None 58 26 55
Brown 44 38 14
10. Nitrogen response of corn, mung and their intercrop at Brown and green strips 49 43 12
two levels of weed control (Nitrogen index: for corn, 50 kg/ha Green 46 42 10
N = 100; for mung, 20 kg/ha N= 100; for corn+ mung, 70 52 days after seeding
kg/ha N = 100). IRRI, 1973 dry season. None 42 42 0
Brown 38 30 21
Brown and green strips 50 51 0

cover (Table 11). When peanuts were planted Green 51 45 12
between the corn rows with and without green burlap, the corn plots with both peanuts and Table 12. Comparison of spider (Lycosa spp.) influx and
green burlap had lower infestations than the preference for solid corn stand or corn-peanut intercorn plots with only peanut, suggesting that the crop. IRRI. June-September. 1973.
moths responded to olfactory cues as well as visual cues. The effects, however, diminished as Spider
the plants grew older perhaps because of the m tlnwt
increasing spread of the corn canopy. 39-43 days after seeding
The survival and establishment of young, From neighboring fields (influx)b 30 32
first-instar larvae which were artificially intro- Within field (preference)c 33 32
duced on the plants were not influenced by the 45-51 days after seeding
peanut intercrop. That is, substances from pea- From neighboring fields (influx)b 35 58
nut in amounts toxic to feeding corn borer larvae 52-5i fays after seein
on corn are not evidently involved. From neighboring fields (influx)' 34 48
A preliminary survey in our experimental corn Within field (preference)c 28 26
fields revealed at least 19 kinds of spiders. Two Avg of four plots, each 12 24 M. bCatches of 20 traps set
species of wolf spiders (Lycosa spp.) were the at both ends of corn rows. cCatches of 20 traps set between
most active and the most frequently observed corn alone and corn-peanut plots.
preying on various insect pests, including young corn borer larvae. Trapping showed that wolf its interaction with the effects of peanut interspiders from neighboring fields move more fre- cropping, borer infestation was compared
quently towards corn plots with a peanut inter- among plots in which spider predation was minicrop than to plots without the intercrop (Table mized by a spider barrier (20-cm-high plastic
12). Within the corn field, however, the spiders wall) and parathion sprays at planting and 1
moved from one plot to the other at more or less week later, or encouraged by allowing free
equal frequencies. spider movement and not treating the field with
To assess the effects of spider predation and insecticides. We found that spider predation conMULTIPLE CROPPING 23

Table 13. Effects of peanut intercropping and spider feasible approaches. Results of our studies idipredation on corn borer infestation. IRRI, 1973 wet cate that one spray treatment with Orthene season.
(O-S-dimethyl N-acetyl phosphoramido-thioBorer infestation ate), a broad-spectrum insecticide, at 35 to 45
Borer stage (no./100 plants) Decrease days after seeding had little or no detrimental
and damage Without With (%) effects, while one insecticide application at 30
peanut peanut
intercrop intercrop days after seeding with or without additional
Spider predation minimized treatments later markedly diminished, if not
Egg masses' 21 16 21 completely nullified, these benefits (Table 15).
Larvae-pupae-pupal cases 69 50 27 Economic implications. Our data on the
Pupal cases onlyb 53 36 33
Tunnels in stalks 115 109 6 eoom retir frm intco ing hacome
Spider predation encouraged
Egg masses 10 7 23 Initial results indicate that the relative profitaLarvae-pupae-pupal cases 80 49 ability of monoculture and intercropping depend
Pupal cases only 58 28 52
Tunnels in stalk 115 89 22 on the management level or on the general growing conditions. With a high level of management aAverage of eight replications: egg mass data based on exami- and good growing conditions, monoculture nation of 120 to 160 plants per replication at 28 days after seeding. bFrom dissection of portion of stalk below ear of 30 seems to give better returns above variable costs sample plants per replication at harvest (88 days after seeding). (Table 16). Return per hectare per day is about
the same, but return per unit of labor is higher tributed to the decreased borer infestation with monoculture. At lower management levels,
(Table 13). Thus the beneficial effect of the pea- or where heavy rains or wet soil conditions renut intercrop was enhanced by encouraging the strict crop growth, intercropping appears superactivities of predatory spiders. On the other ior for total return above variable costs, return
hand, the regular use of the broad-spectrum above variable cost per hectare per day, and
insecticide, azinphosmethyl, diminished these return per unit of cash expense. It is about the
benefits; even the use of the more selective bio- same as monoculture in return per unit of labor. logical insecticide, Bacillus thuringiensis, was The amount of labor used is higher in intercropdetrimental but not as much as the nonselective ping. It seems likely, based on very limited data,
insecticide (Table 14). Evidently, to maintain that intercropping may best fit in land-limiting,
and encourage beneficial effects of intercropping labor-surplus situations. It also may be far more on insects as management levels are increased, productive under situations where management
considerable planning and judicious insecticide is less than optimum for monoculture.
treatments are required. Proper timing and placement of insecticides seem to be the more 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 Table 14. Influence of insecticide treatments and spider season. predation on decrease in corn borer infestation from corn-peanut intercropping. IRRI, 1973 wet season. changein
Date of spraying larval feeding holes in
Change due to peanut intercropping* (%) stalk due to peanut interTreatment Survival 29 DS 36 DS 44 DS 50 DS cropping' (%)
ovipositionb Late instare Early instard 24
~/ --22
Azinphosmethyl* -10 9 -12 -36
B. thuringiensis! -42 -13 -18 -17
No insecticide -51 -26 -32 V -19
./ -25
From paired comparison of plots, 12 mx 24 m each, of corn 6
alone and corn-peanut intercrop; corn population, 40,000/ha. V -25
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, Days after seeding. bprom paired comparison of plots. 5 x 6 m and 62 days after seeding. e0.05% a.i. solution. 'Dipel applied each, of solid corn stand and corn-peanut intercrop, mean of 22, 23, and 38 days after seeding. readings at 50, 57. and 72 days after seeding.


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

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 CES 16-23, were high yielding but susceptible to
Mungdisease. CES 16-103 has an excellent plant type frm ndi band Durng the year, d 47 cmngllcin with a stiff, erect stem. Thirty vegetable soybean from India and from the U.S. world collection tyewreiroudfomsban reig
were added to our collection, bringing the total tatos intpa.e re earlyan yeed
to more than 600. The best 12 lines from two well. in ave high pre and lowloil
seasons of testing were compared in solid stands conTe ans have less viai prol
and also interplanted in corn (Table 17). The inte trpishan he es withihigherolevs Philippine varieties MG50-10A and CES 55 fo temperat es.pMs ofth ereely
continued to yield well in solid stands as well as m at and s st onm data
when interplanted in corn. Interplanting did not show a sstatured t
change the time to flowering, but caused the plants to grow taller, to have heavier infestation the aves a the tea level and
of leaf disease, to have fewer pods, and to become senescent earlier (Table 18). Seed size was marketing the whole stem for an extremely high reduced only slightly. The interplant trials were grown with 40,000 plants/ha of Early Thai Com- Table 17. Highest yielding mung bean varieties. IRRI. posite corn at a high fertility level, shifting the 1973. balance in favor of corn. Data from other trials Yield' Relative yield when
indicate that a decreased corn population would Variety (no corn) planted in corn
not change overall productivity but would shift (t/ha) (%)
the balance in favor of mung. Testing mung CES 28 1.70 28
varieties under a corn population that would MG50-10A 1.60 36
allow mung to yield 50 to 60 percent of that in a M 350 1.59 24
CES 55 1.58 37
pure stand would probably show varietal differ- M 198 1.56 33
ences better than the 37-percent average that was MD 15-2 1.55 26
achieved for the 18 varieties we tested (Table 18). -8 (yellow) 1.53 24
MG50-10A (yellow) 1.41 42
Soybean. Of the soybean varieties previously M 304 1.39 41
tested, Multivar 80 continued to yield well M 79 1.37 40
(Table 19). Two new breeding lines from the M 205 1.29 43
University of the Philippines at Los Bafios M_157_1.24_41
(UPLB) College of Agriculture, CES 16-103 and Mean yields from two seasons of replicated trials.


Table 18. Response of 18 mung bean varieties to inter- Table 19. Highest yielding soybean introductions. IRRI. cropping in corn. IRRI, 1973 dry season. 1973 dry season.

Character Mung With Variety Yield Maturity Plant Pads Rust
alone corn (t/ha) (days) ht (cm) (no/plant) rating
Yield (t/ha) 1.5 0.6 CES 16103 2.94 80 51 34 3.8
Time to flowering (days) 31.1 31.2 Kuro-daizuc 2.94 109 120 71 4.0
Maturity (days) 63.4 55.8 Multivar 80 2.89 84 84 28 3.0
Height (cm) 65.2 72.4 CES 16-23 2.70 90 108 44 2.2
Pods (no./plant) 11.6 5.0 Higo-daizu 2.39 70 46 30 1.0
1000-seed wt (g) 53.5 49.2 Shirodaizul 2.30 98 114 48 4.0
Cercospora and rust, 3.8 4.5 Hsih Hsih 2.31 73 39 30 1.0
Lodging 2.4 2.4 Ao-daizu 2.22 90 36 24 3.0
______________________________ Kimusume 2.20 69 48 28 1.0
'1 = slight, 5 = severe. 1= little, 5 = heavy. 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
return. Protein production per day as well as Higo-musume 2.09 69 38 29 1.0
per unit of labor is high. lyo-daizu 2.04 74 34 37 3.0
Cowpea. Two groups of cowpea accessions Gin-ai 1.99 82 4 3 3.0
were tested. Of 18 breeding lines and accessions Tainung 3 1.92 84 66 39 2.8
from UPLB several appeared promising (Table Fuji 1.90 68 42 27 1.5
20). From 143 lines received from the Asian Haiga 1.85 80 4 3 2.5
Vegetable Research and Development Center E.G. Special 1.68 78 70 29 4.0
in Taiwan, 13 appeared to have promise. The TK5 1.58 80 66 41 3.5
lines were tested in an early rainy season plant- LSD (5%): 0.24. b1 = slight, 5 severe. cSuitable for late ing when light intensity was low, tending to make planting. the varieties viny and indeterminate. That perhaps explains why few of these lines looked good. Binongko, and Penjalinan, were introduced and Cowpea is the crop in our systems with the increased. Penjalinan appeared to be the most
greatest need for varietal improvement. The promising. It matures in around 70 days, prolack of determinate growth habit and suscepti- during 3 t/ha in the dry season and about 2 t/ha
bility to virus and soil-borne disease limit its in the wet. Its only use appears to be in intercrop usefulness in intensive systems. combinations, but it is questionable whether the
Sweet potato. In trials of sweet potato varieties, 10-day shorter growing period compensates for BNAS 51 was consistently superior under both the lower yield when compared with Thai Early
wet and dry conditions. In a time-of-harvest Composite. It fits better the growth cycle of rice
trial, BNAS 51 yielded far better than Centennial in intercropping than does Thai Early Compoat all harvest times (fig. 11). The nitrogen level site. necessary for high yield seems critical. Nitrogen
levels above 100 kg/ha reduced yield of tubers
even with intercropping. The required fertility Ridge-and-furrow rice growing. A final year of management of sweet potato intercrop combina- testing of the ridge-and-furrow method of growtions thus appears to be quite different from that ing rice strengthened the notion that it has little of corn-rice or other combinations. application on the heavy Maahas clay soil of the
Corn. The key corn varieties we use are Thai IRRI farm during the wet season. Early in the Early Composite and DMR-2, a 97-day maturity 1972 wet season, we began to prepare the soil in
variety from the Philippines. Thai Composite an upland condition with broad furrows separadeveloped black layer in 85 to 87 days. Its yield ted by narrow ridges at I-meter spacing. On potential is 6.5 to 7.0 t/ha in the dry season and September 7 after several aborted attempts at 4.0 to 4.5 t/ha in the wet season under Los land preparation, weed control, seeding, and
Bailos conditions. DMR-2 is resistant to downy reseeding, a uniform stand of rice was finally
mildew, but is later and has a lower yield established. During July and August, each time
potential. Three Indonesian varieties, Pakelo, after the fields had been prepared and the rice


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

Growth Disease rating Plant ht Days to Erect or
Accession character' Mosaic virus Wilt (cm) maturity' creeperd
Mecan pea SD 1 1 200 75 SC
Red cowpea 6-1 D 2 1 65 71 E
Cowpea #18 D 2 2 59 68 E
Red cowpea #6-14 SD 1 2 110 66 E
Cowpea #16 D 2 2 63 65 E
Red cowpea 6-12 W D 1 2 80 69 E
Virginia 67-3 D 2 2 70 71 E
Cowpea #15 D 1 2 60 69 E
Cowpea #23 D 1 1 62 76 E
Cowpea #21 D 2 2 51 66 E
Cowpea # 14 D 1 2 63 72 E
Virginia crowder D 2 3 59 70 E
Cowpea #33 D 2 3 60 72 E
Red cowpea SD 3 2 136 71 SC
Cowpea #32 D 3 3 54 71 E
Red cowpea 6-12G D 3 2 52 69 E
Cowpea #22 D 2 2 555 71 E
*SD = semi-determinate; D = determinate. b1 = 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 type of ridge and furrow. Vegetables (cabbage
which restricted rice emergence because of and Chinese mustard) were planted on the
waterlogged soil and a thinly puddled surface ridges in a portion of each plot. Rice yielded
layer. To have the precision of land preparation better in the puddled furrows (Table 21). The required in this method it should be done with higher yield with vegetables is a result of higher
irrigation before the rains start. The narrow nitrogen levels in these treatments. Considerably
range of soil moisture that allows good work- more water was required to maintain standing
ability of Maahas clay limits the time when it can water in the puddled treatments as compared be prepared once the rains start. On a lighter, with maintaining the upland area at close to
better drained soil the method may be feasible field capacity by flushing with water every 3 to
either with irrigation in the dry season or at the 4 days. At higher nitrogen levels, however, start of the monsoon.
In the trial, rice responded to nitrogen only Tube yield tha)
up to 100 kg/ha levels. There was a response to 6
seeding rate up to 90 kg/ha but only at nitrogen levels below 100 kg/ha. Both IR8 and IR20 showed similar responses. 28
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 20
furrows, was tried in the hope that this might add stability to the system during rainy periods. Here, Centential
again, however, the problems of soil and water 12
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 _L
0 60 70 80 90 00 110 120
direct-seeded in all treatments, with three differ- Days after transplanting
ent seeding methods on puddled furrows and 11. Growth rates for the two best yielding sweet potato
the standard three-row planting on the "upland" varieties.


Table 21. The effect of seedbed preparation and seeding method on rice yield and water-use efficiency. IRRI, 197273 wet and dry seasons.

Total Water-use efficiency
Planting method Rice yield (t/ha) Water use (mm/kg of rice)
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 crops with rice at the end of the rice-growing treatments. On heavy, low-lying, poorly drained season is common. We tested crops relayed into soil, management difficulties and high risk pre- 1R8 rice at different times before harvest to comclude the use of complex management systems. pare their relative tolerance to shading during The more simple and straightforward the method early growth stages. Mung bean had little tolerthe greater the long-term payoff. dance to shading past the first week (fig. 12). SoyRelay cropping after rice. In intensive cultiva- beans and cowpea showed more gradual tion systems in Taiwan, relay planting of upland reductioninyieldwithincreasingtimeofoverlap.
Corn was especially sensitive to shading but Yield (t/ha, log sole) sorghum was relatively tolerant for 14 days.
7.0 Sweet potato showed little effect of overlapping.
6.0 Soybeans (green) Rice yields were not affected. The rice canopy
5.0 -was completely closed over the narrow ridges 4.0 Sorghum (of the ridge-and-furrow system). This together
with the low light intensities of the late rainy 3.0 season heightened the competitive effect of overlap on the crops that followed rice.
2.0 Effect of puddling on crops after rice. To test
the Taiwan method of building "Poa" ridges in Cornpuddled rice for following crops, we compared this method following puddled rice with crops 1.0 grown on nonpuddled soil following upland
rice. The building of ridges in puddled soil before rice harvest required 450 to 512 man-hours/ha Cowpeadepending on the method used. These ridges had 0.5 to be cultivated after the rice was harvested. The
nonpuddled plots required 13 h/ha of handtractor use to prepare the seedbed. It was mung 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).

0 7 14 21 Crop residue problems. To reduce the cash outlay
Number of days overlap fo nirgni. nesv rpigssesa
12. Quadratic relationships between yields of different cropsfonirgnnitesvcopngytmsa and number of days of overlap with rice, IRRI, 1972 wet well as to conserve a commodity which will season. become increasingly scarce and more costly in


the future, we are attempting to use grain legumes Table 22. Yield of crops following rice on puddled and more frequently. unpuddled soil. IRRI, 1972 wet season.
One problem we encounter with grain legumes Yield (t/ha)
that yields drop when they are grown more Ntoe ple is tayilsdowhnteargrw moe (kg/ha) Corn Sorghum Green soybeans Mung
frequently than once a year. When cowpeas were
used, soil-borne disease built up rapidly, but this 60 2.6 2.8 4.8 0.6
did not seem to happen with mung and soybean. 100 2.4 3.5 5.7 .4
Nematode build-up was likewise ruled out. To 150 3.0 3.1 5.5 .5
study the effect, we planted mung, cowpea, and 60 2.6 3.1 4.2 .5
corn for one season in a split-plot design. Then 100 2.2 2.7 4.1 .5
after harvest the same three crops were planted 150 3.2 3.1 4.8 .7
again in each of the plots at three levels of nitrogen. The yields of mung and cowpea were much
lower after mung or cowpea than after corn Weed management. On experiment stations,
(fig. 13). Corn yields were not affected by the standard cropping with high levels of chemicals, previous crop. There was no significant inter- intensive tillage, and relatively low leaf area action between the effect of previous crop and indices nearly always results in a shift of weed nitrogen level, indicating that the difference was species to predominantly grasses and sedges. not due to nitrogen. Otherwise, corn would have With high rainfall during the monsoon on a shown an even greater differential than did the heavy soil these species are extremely difficult to legumes, since it is generally more nitrogen re- control. In farmer's fields, where field crops make sponsive. Rice grown in the third season after full use of the seasonal moisture supply, this type these combinations showed no effect at all from of weed climax is seldom found, even if several previous crop combinations. The effect seems crops a year are grown in intensive patterns. especially prevalent on heavy soil that has Instead weed communities are composed of a moderately poor drainage. Corrective studies very few species, usually broadleaved weeds. In indicate that the response may be different de- many areas traditional cropping patterns apparpending on the crops causing the effect. Mung gently have this built-in weed balance. Our goal following certain combinations of crops re- is to learn how to manage this shift while giving sponds to ferrous sulfate in addition to complete economic control in each crop. fertilizer. There seem to be no interactions in In a continuing year-round experiment at sensitivity between mung varieties and the IRRI, we have imposed four levels of weed residual effect. management on two cropping patterns. We have

Sweet corn ears t/ ho Mung yield kg/ha) Cowpea yield (t/ ha)
12 10
(gh after corn G000
60 2. 2. 4. 0.6
1080430 .7 .

I after m cn rn
,f6 2.6e 3.1pe 4.0.

8 I
T15 3I 3.O0 1 4. .7

0 50 125 200 0 250 025 50
Nitrogen peied (kg/ho)
13. Yield of sweet corn, mung, and cowpea as influenced by nitrogen level and preceding crop. I RRI, 1973 dry season.


Table 23. The effect of density of leaf canopy on indi- died for one crop or even flooded for several vidual weed species. IRRI, 1973. weeks during the rice season, the effect on the

Weeds under low weed community and on subsequent control
density crop requirements is dramatic.
Weed species canopy (no./sq m) Ratio To learn how to manipulate the shift of weeds
1st 2nd 1st 2nd under different cultural practices we are studyseason season season season ing several species which are predominant in Digitaria sanguinalis 1325 79 0.80 0.40 fields having "experiment station" technology Echinochloa colonum 181 48 0.60 .69
Eleusine indica 39 40 1.22 .69 and also some from farmer's fields. Weeds vary
Portulaca oleracea 126 153 1.06 .65 in response to population and to shading. PortuAmaranthus viridis 17 23 0.19 .29 laca oleracea shows little increase in dry weight as
Cyperus rotundus 59 138 0.93 .22 plant population increases above a low level but
80f weeds at high crop density compared with weeds at low its response to nitrogen is nearly linear up to crop density. 150 kg/ha (fig. 14). It is quite sensitive to shade
(fig. 15). That helps explain why it becomes prehigh and medium levels of management using dominant in intensive systems under high
chemicals and mechanical tillage under crop fertility and low leaf area index, for example,
patterns of high and low leaf area index. The where vegetables are grown intensively. Cyperus combination of control method and leaf area iria has a much greater population response but
index after two seasons has already caused a it responds to nitrogen only up to 75 kg/ha in the
marked shift in weed species (Table 23). Several wet season. Ipomoea triloba shows a shadeshade-sensitive grass species and sedges, especi- tolerance pattern. Shade may have an even ally Cyperus rotundus, have decreased markedly greater effect through reduction of seed yield and under the high leaf area index. It may be possible subsequently on population shift than through to shift the year-round, seasonally changing reduction of dry matter.
weed pattern toward species which are more Management of arthropods in crop liter. In
easily controlled during the early growth stages intensive cropping patterns, the handling of crop of each crop. In patterns where the soil is pud- stubble becomes a problem, especially where

Dry weed wt (g/sq m) Reduction in dry wts
500 100
requiement is dramatic.
400~T le r howh tonit manipulate thee shif of weeds,

high density Portulaca leroce l

its rsoe to ntoe is low density 40 t

15 kg/h (fig.04 1p4i noe t o sa
(fig 15). TYP h eus iwa
dmnlow density 20i

01 0
0 75 150 0 20 40 60 80 tOO
Nitrogen level Shade s)
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.


power is limited. Burning is seldom used in Table 24. Total nitrogen content of above-ground plant
intensive systems except in lowland rice. One parts in corn-rice intarcropping at maturity. IRRI, 1973 reason is that during wet weather the intensive we,_season, schedule does not permit drying. Another is that Crop Nitrogen content (kg/ha)
following burning, nutrient loss by leaching is Corn Rice Corn + rice
much higher. It appears that on small farms 60 kg/ha N
cutting the crop and allowing the stubble to Corn 104
decay between the rows of the succeeding crop Rice 95
Corn + rice 52 61 113
will continue to be a common practice. 120 kg/ha N
In intensively cultivated soils, organic litter Corn 81
turn-over rate decreases, which may affect Rice 62
Corn + rice 58 54 112
natural buffering capacities of soils and bene- 180 kg/ha N
ficial biotic relationships in cultivated fields. For Corn 95
this reason the role of arthropods in hastening Rice 68
Corn + rice 85 56 141
organic decay is important. 240 kg/ha N
A survey of arthropods associated with de- Corn 99
composingcorn,mung, and peanutlitterrevealed Rice 91
Corn + rice 73 67 140
that stratiomyid flies, oribatid mites, and collembolans are the dominant agents of litter
breakdown. Careful counts revealed representatives of 11 orders of macroarthropods and two been biased in favor ofmonoculture. The greater orders of microarthropods. There were four sub- efficiency of uptake in the intercrop was reflected orders of Acarina represented by 27 genera. Pre- in a higher gross return (Table 5). datory arthropods like spiders, dermapterans, Power source interactions. The farmer's power and macrochelid mites were also abundant. As source plays a critical role in intensive systems. expected, the population of these arthropods In a replicated trial with large plots, six crops varied with the type of litter; they also responded were grown under irrigation during a 1-year differently to a treatment of the litter with period. Rice was started in June and relay molasses as a food energy source (1 : 3 mixture planted with sweet potato. This was followed in of molasses and water) which was applied as a February with corn interplanted with cowpea drench to boost initial microbial activity. Stra- and in May by corn interplanted with mung. We tiomyid larvae, for instance, increased more compared three power sources-hand labor, rapidly on peanut litter than on corn. hand labor plus carabao, and hand labor plus
Nitrogen utilization. Some intercrop combina- hand tractor.
tions like corn-rice not only have a higher total The three sources showed little difference in productivity but also make more efficient use of total costs and returns (Table 25). Since the nitrogen. In the corn-rice trial, the total nitrogen methods were about the same in net return, the uptake was considerably higher with intercrop- choice of power source can be made on other ping (Table 24). This cannot be explained solely criteria. The cash flow of the systems, assuming by greater total light interception, since the that a farmer hired the labor, carabao, and traccombination did not have a much higher level tor, was slightly in favor of hand labor. Less than rice alone except during the early weeks of money would be required to pay for the early growth. Probably, light interception was not land preparation and thus a smaller cash outlay only slightly higher but also more efficient. The would be required early in the season. Return on rice crop in the trial was affected by an early labor was of course greater with the machines infection of blast at nitrogen levels above 60 than with carabao or hand labor (Table 26). kg/ha. Fungicidal sprays kept incidence low Return per unit of cash expense was higher with enough to give later recovery at higher nitrogen hand labor than with other methods (Table 27). levels. The incidence of blast was greater with Different power sources thus fit different recorn interplanting, so the response may have source patterns.


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

Consideration of timing of operations, how- that of labor and power inputs, indicating an
ever, gives a quite different picture. If a farmer unrealistically high proportion of energy, for has 1 hectare of land and three man-units of Southeast Asia, from modern chemical inputs.
labor in addition to one carabao or one hand These relationships have important implications
tractor, the advantage weighs heavily in favor on a national scale. of the mechanized operation. With one tractor Economic comparisons of modem intensive
the cropping pattern would have been roughly as production. In evaluating economic returns from accomplished at IRRI with the land being cropping patterns it is best to take data from
unplanted 7 percent of the time. With a carabao farmers' fields which are in routine production. and three men, I additional month would have With new patterns, however, the farmer must be
been required, with the land idle 16 percent of induced to grow them or the researcher must do the time. With hand labor only, 2 more months it himself. We are currently using both methods,
would have been required, with the land idle with the more complex irrigated patterns being
22 percent of the time. If weather conditions tested at IRRI.
were not favorable for field operations all of the The managed plots at IRRI are set up in four time, the hand labor system would take still replication. The first replication is 25 x 25 m longer since field preparation could not be car- and is used for yield and for labor-use studies. ried out during the expected brief periods when The remaining three replication are 7 x 25 m. weather conditions were favorable. With hand The 25-i-row length permits hand tractor or
labor only, and a limitation on labor, two crops carabao operations so that management simuper year is a more reasonable pattern. latest that of a farmer's field. During 1972-73,
The total energy balance of the three methods five 1-year patterns were set up to compare is surprisingly similar (Table 28). Hand labor productivity and returns (fig. 16). The level of has a slight advantage in efficiency over other management was patterned after what a good power sources but not as great as some reports farmer might use. The patterns included comindicate. The energy equivalent of the cash binations of rice and legumes; rice, legumes, and
input was, surprisingly, three times higher than
Table 27. Return over variable cost per peso of cash
Table 26. Return over variable cost per hour of labor, expense.
Return (S thh'e) Return (P/P cash expense)
Crop Hand labor Hand labor + Crop Hand labor Hand labor +
Hand labor + carabro hand tractor Hand labor + carabao hand tractor
Rice 0.80 1.20 1.70 Rice 0.00 0.30 0.30
Sweet potato 4.30 6.40 9.00 Sweet potato 7.50 5.10 5.10
Cowpea and corn 2.10 3.30 4.40 Cowpea and orn 2.00 1.90 2.00
Mung and corn 1.70 1.50 2.20 Mung and corn 7.50 1.50 1.50
Total pattern 2.20 2.60 3.70 Total pattern 3.50 2.80 2.00


vegetables; and rice, a root crop, and a feedgrain. PATTERN Cash and labor inputs were expected to vary RICE COWPEA SWEET CORN
widely between patterns.
Yields and returns were affected not only by PATTERN 2 the season and amount of rainfall, but also by RICE
the market price at the time of harvest (Table 29). S O.
Labor requirements and returns varied from 36 PATTERN 3 man-hours at P3/man-day to 275 man-hours at W I ;TBELN Z
P25/man-day. Rice yields and returns were low because of a severe outbreak of grassy stunt PATTERN 4
virus. The highest return was P104/man-day on RICE BS
112 hours for corn-sweet potato. With many TAO
legume crops like mung, the cash return and PATTERN 5
protein production were considerably higher when intercropped. Otherwise mung is profitable ICE TOMATO MUNG TOMAT
only with little management. The soybeans were I
low yielding presumably due to the residual J A S 0 N D J F M A M J J A
effect of the preceding cowpea crop. Normal 16. Crop sequence and timing of five irrigated cropping protein production of green soybeans should be patterns.

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

Energy balance (MCaI/ha)

Power Power Other variable Total energy Marketable energy
source i nputs 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-0.1 75 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/ P1.

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

Crop Yield Labor Return above variable Marketable digestible
(Iha) (man-day/ha) cost (P/ha) Protein Nutrients
Total Per man-day Total Per day (kg/ha) Tomato 24 133 3,320 25 67 0.8 70
Tomato and 20 256802 3 4
bush sitao 0 256802 3 4
Okra and 21275,22047 .176
mung 0.5275,22047 4176
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 71111601424 .918
sweet potato 251111601424 1918
Corn and 564150296 .400
cowpea 064150296 1400
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


Table 30. Labor requirements, productivity and returns from five irrigated cropping patterns.

Cropping Labor Marketable digestible Total return Return above variable cost ( P)
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 with legumes alone. Careful mixtures of legumes, the combination are extremely high in produc- grain crops, and root crops have exciting potention of total digestible nutrients. trial, not only for high levels of nutrient producVarious measures of returns for the overall tion, but also for total productivity.
cropping pattern showed similar trends (Table Using the resource-utilization approach, it
30). Rice followed by legumes (pattern 3) gave seems evident that for many farmers novel types
the lowest return on labor and cash expense as of technology may be quite relevant. It is also
well as lowest total nutrient production. Total clear that huge gaps exist in our knowledge of return and return on investment are not closely cropping systems for the Asian rice farmer. The related to nutrient production, especially when effect of soil tillage properties on cropping pathigh-return vegetables are included. If a vege- tern potential has not been studied. To reach table market were not available, and especially our long-range goal of eventual modeling of if labor supply was limited, pattern 2 seems far cropping systems, we must fill in several of these more attractive than the other patterns. If labor gaps before our model can hope to be useful. For is more plentiful, pattern I offers increased the present, however, there seem to be several
employment with a high return. ways in which simple changes can be made to
It thus appears that protein and total nutrient improve production efficiency for the Southeast productivity can be made profitable, but not Asian rice farmer.


S as i 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 management. We used a factorial combination of several cultural practices each at two levels: the farmer's level and the recommended level. El While both genetic and non-genetic variances of protein content are smaller than those of grain yield, the ratio of these variance components is much more favorable for grain yield than for protein. Moreover, 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 response functions in 1,047 out of 1,304 response curves examined.

FACTRS IMIINGFARMRS YILDS seedling management, each at two levels, was
FACTORS LIMITING FARMERS YIELDS conducted at several farms in the 1972 dry and
Despite the rapid adoption of the improved rice wet seasons. In the 1973 wet season, only four varieties, farmers achieve only a small fraction factors were tested (water management was of the varieties' yield potential. The usual way to excluded). The sample farms were purposely study the causes of low farm productivity is a selected based upon reported yield levels. The survey in which information on yield and cultural two levels of each factor tested were (i) the practices are obtained from sample farms, farmer's practice, that which the farmer of the usually through interviews. But yield variation sample farm actually used (thus it varied from among farms can not be totally explained by one sample farm to another), and (ii) the "imcultural practices alone-climatic and soil differ- proved" practice, the standard practice used in ences are at least as important. To remedy this, IRRI field experiments. The improved practice some studies include the monitoring of the consists of 120 kg/ha N in the dry season and
physical environment throughout the growing 90 kg/ha N in the wet season, 3 to 5 cm of standseason. The major disadvantages of that ap- ing water maintained up to 2 weeks before
proach are that monitoring climatic conditions harvest, as close to weed-free condition as is laborious and time consuming, and that data possible, maximum protection against insects on physical environment can be highly useful and diseases through application of insecticides, only if its relation to yield and other cultural and use of dapog seedlings, 10 to 13 days old, practices is known beforehand. grown from breeder's seed from IRRI or from
Since the limiting factors that are of major the University of the Philippines at Los Bafios. interest to rice researchers and farmers are those Aside from yield, data on weeds, off-type that are within human control-management plants, rat damage, and insect and disease
and cultural practices-we have evaluated a incidence were collected. A complete record of
procedure for removing the complications eman- all management and cultural inputs from seedating from large climatic and soil differences ling preparation to harvest was kept for both the from one sample farm to another. The procedure farmer's practices and the improved practices. consists of obtaining sample farms as is norm- Relative contribution of inputs to yield increase.
ally done in surveys and conducting field plot In the dry season, improved practices greatly experiments on the farms to obtain information increased yields in farmers'fields compared with from actual measurements instead of from the farmers' practices (Table 1). On one farm imfarmer. proved practices gave a yield of 9.6 t/ha. The
A factorial experiment involving (i) insect absolute yield increase ranged from 2.4 t/ha to control, (ii) water management, (iii) weed 4.4 t/ha (about 50 to 300%). Each input gave
control, (iv) fertilizer, and (v) seed source and some yield increase but insect control, fertilizer,

Table 1. Contribution of five management inputs toward improving rice yields in farmers' fields. Laguna, Philippines. 1972.
Fwet se.Grain yield (ttha) Contribution (t/ha)
no. planted Farmer's Recommended Difference Insect Water Nitrogen Weed Seedling
inputs inputs control management fe ilization 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 IR18 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


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)
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
'Data not available.

and water management, were the most crucial minimized, yields on these farms were raised
in raising rice yields in these farms. They contrib- 1 t/ha, irrespective of season. In the dry season, uted an average of 83 percent to the total yield improvement in water management could raise increase. Their effects, not unexpectedly, varied yields 0.9 t/ha and the use of higher nitrogen greatly from farm to farm, since the level of rates could raise yields 0.7 t/ha. Improvement in farmers' management varied greatly among weed control management as well as in seed
farms. source and seedling management compared with
In the wet season, the level of yield increase the farmers' practices did not seem to give due to improved practices was generally low, appreciable effects.
averaging only 0.6 t/ha or 14 percent. Of the five Evaluation of techniques. An important aspect factors tested, insect control and weed control of the proposed procedure is the experimental caused the entire yield increase, although the design or the choice of treatments to be tested. increase was not large. As expected, water If interactions among the various inputs exammanagement was not as big a problem in the med are appreciable, then factorial treatments,
wet season as in the dry season. Moreover, while whether complete or incomplete, may be more in the dry season, some improvement in the desirable than the discrete management packfarmers' nitrogen fertilization practices (avg: 87 ages. The use of complete factorial treatments, kg/ha N) was possible, it was not so in the wet of course, may enlarge the size of the experiment season (when farmers used an average of 65 which is undesirable, especially for trials in
kg/ha N). farmers' fields. During 1973 wet season we
The 1973 wet season trial confirmed these experimentally evaluated some of the possible
results (Table 2). Again, insect control ranked interactions among the management inputs with as the most crucial factor in improving rice the average farmers' level as control. We found
yields in the farms, giving an average yield that weed-control level gave a large differential
increase of 1.3 t/ha, which is 68 percent of the effect on the nitrogen response of rice (fig. 1), total yield increase. Weed control was the second indicating that an optimum nitrogen rate derived most important factor with an average yield from fertilizer trials conducted at experiment
increase of only 0.3 t/ha. stations under high management levels may not
The greatest yield constraint in farmers' fields necessarily be appropriate under farm conditions in the study area seems to be control of pests and having lower levels of other management inputs. diseases. When pest and disease problems were Virus incidence (grassy stunt) was observed to


Groin yield (t/ha) the agreement between grain yield of farmer's
paddy and that from experimental plots receivWeeded ing the farmer's level in all the factors tested.
92.53 + 0.0122N(R2=0.932**) Results of 1973 wet season indicated no bias in
the simulation technique (Table 4). In most
farms, the agreement was good; only three farms 3 0 0 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
0 simulate. Application made 1 or 2days later than
2-01 Non-weeded the farmer could make a great difference since
Y= 1.50+0.0295N-0.00019 N2 the effectiveness of insecticides depends on (R2 =0973*) weather conditions, particularly rainfall.
Placing plots with low insect control level (farmer's practice) adjacent to those with high 0 insect control level (improved practice) tended
0 30 60 90 120
Nitrogen applied ( kg/ha) to give a slight overestimation in yield (Table 5).
1. Nitrogen response of rice (IR20 and IRi561-228-3) grown Moreover, because ofthe difficulties encountered under intermittent irrigation, as affected by weed control insimulatingfarmer'sinsecticidepracticesitmay levels. IRRI, 1973 wet season. be more practical to have the insecticides applied
by the farmer himself even on the experimental be higher under continual flood irrigation condi- plots. These findings suggest that the two sets of tion than with intermittent irrigation, and slightly plots according to the insect control level should higher in weeded plots than in nonweeded plots be separated to avoid a possible bias in yield as
(Table 3). These results seem to indicate a great well as to facilitate the farmer's insect-control dependence of the benefit of one input on the operation.
levels of other inputs, and the danger of extra- For conducting this type of experiments in
polating results obtained under experimental farmers'fields, aplotsize that gives a net harvest
conditions to farmers' fields where the level of area (after exclusion of border rows) of 6 to 8 input use is generally lower. Because of the sq m per plot seemed sufficient (fig. 2).
apparent importance of interaction effects, In two seasons of tests in 1972, the experifactorial treatments should be used in this type mental procedure was not satisfactory for
of experiment. assessing the contribution of water management
The validity of the proposed approach de- to farmers' yields. We had great difficulty in
pends greatly on the success of the simulation of maintaining the desired water level for farmer's practices, which can be measured by "improved" plots because water was not availTable 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).
thed simuatio techVirus incidence (%)
level management 0 kg/ha N 30 kg/ha N 60 kg/ha N 90 kg/ha N 120 kg/ha N_ Avgb
Non-weeded Continuous flooding 3.9 2.7 5.2 4.8 5.7 4.5 c
Intermittent t 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 da
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
MMostly grassy stunt. bMeans followed by a common letter are not significantly different.


able at all times. Other procedures should be Experimental error g/Sq M
evaluated, such as sampling from farms that have been stratified into various categories of water availability. 1200

Two problems widely believed to hinder the improvement of grain protein in rice are that protein content is highly influenced by environ- 800 (R2=Q993*)
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 4
between protein content and grain yield.
Phenotypic variance within varieties. Experimental data on protein content and grain yield of IR8 and IR480-5-9 from experiments conducted by the agronomy and varietal improvement departments were analyzed. We found that the 0 L J
0 3 6 9 12
variability due to environment constituted a Harvest area per plot sq m
substantial portion of the total variability in both 2. Relation between experimental error and net plot size for protein content and grain yield. In 964 experi- rice experiments in farmers' fields. Bay, Laguna, 1972 dry
mental plots of IR8, brown rice protein ranged season.
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 grain yield and protein content, we found that
(fig. 3). Protein content varied greatly among improved water management and weed control
locations (Table 6) and among cropping seasons increased both (Tables 8 and 9) too. On the other
(Table 7). In addition to plant density, nitrogen hand, improved pest and disease control infertilization, and method of nitrogen application creased grain yield without affecting significantly previously shown by IRRI agronomists to affect protein content (Table 10).

Table 4. Grain yields obtained in farmer's paddy and from simulation of farmer's practices in experimental Table 5. Yields of plots in farmers fields receiving low plots, under varying farm conditions. Laguna, Philip- levels of insect control adjacent to or separated from pines. 1973 wet season, plots receiving maximum insect control. Laguna,
Philippines, 1973 wet season.
Variety Yield (t/ha) Grain yield (t/ha)
planted Simulated Farmer's Variety
farmer's plots paddy Difference planted Adjacent Separated Difference
IR20 5.0 4.2 0.8 1R20 5.3 4.9 0.4
IR20 1.5 1.3 0.2 IR20 2.2 1.5 0.7
IR22 4.1 3.9 0.2 IR22 4.9 4.1 0.8
IR22 1.9 1.7 0.2 IR22 2.2 2.1 0.1
IR1561-228-3 4.5 5.5 -1.0 IR22 2.5 2.2 0.3
IR1561-228-3 3.4 3.5 -0.1 C4-63G 2.9 1.7 1.2
C4-63G 1.7 1.2 0.5 C4-63G 2.0 2.1 -0.1
C4-63G 2.2 2.4 -0.2 C4-63G 2.9 2.7 0.2
C4-63G 2.3 3.1 -0.8 C4-63G 3.0 3.3 -0.3'
C4-63G 2.2 1.8 0.4 C4-63G 2.7 2.2 0.5
Avg 2.9 2.9 0.0 Avg 3.1 2.7 0.4


Experimental plots (no.)

R=8.2% X=56t/ho R=459kg/ha
150- cy= 13% cy=28% cy-32%



5.9 69 79 89 99 10.9 119 09 2A 3.3 46 58 70 82 94 124 268 412 556 700 844
Brown rice protein (%) Grain 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 application significantly influenced experimental only was generally lower than that of grain yield errors of both grain yield and protein content (Table 11), its magnitude was also less influenced with the lowest errors obtained when nitrogen by the cultural practices employed. While the was applied in split dose-basal and at panicle
experimental error of grain yield was greatly initiation (Table 13). Thus the test condition reduced with nitrogen fertilization (Table 12), that minimizes experimental error for grain yield that of protein content was not appreciably is also appropriate for protein.
affected. On the other hand, method of nitrogen Data from 964 experimental plots of IR8 and
538 plots of IR480-5-9 grown under varying
Table 6. Brown rice protein and grain yield of IR8 environmental conditions at IRRI farm revealed (unfertilized) grown in agronomy trials at four locations quadratic relationships between grain yield and in the Philippines. 1969 wet season (Data are averages percentage protein content (fig. 4). Grain yield of three replications). and protein content increased simultaneously
Location Protein (%) Yield (t/ha) only up to a point beyond which an increase in
IRRI 7.5 + 0.2 4.7 0.1 protein content resulted in a decrease in grain
Bicol 7.1 0.3 4.6 0.5 yield. This suggests that there is a protein
Maligaya 6.7 + 0.1 5.2 + 0.1
Visayas 5.5 + 0.4 4.0 0.2 threshold representing each variety's grain protein potential. For IR8, this protein threshold
was estimated at about 8.5 percent, with a
Table 7. Brown rice protein and grain yield of six rice corresponding average grain yield of 6.6 t/ha in varieties as affected by crop season. IRRI. 1971-1972 the dry season and 5.1 t/ha in the wet season. (Data are averages over two trials each with three For IR480-5-9, a promising high-protein line, replications).
replications).____________ the protein threshold was about 10.3 percent
Dry season Wet season with average grain yield of 6.5 t/ha for the dry
Variety Protein Yield Protein Yield season and 4.3 t/ha for the wet season.
(%) (t/ha) (%) (t/ha) Phenotypic variance among varieties. A series
IR8 7.1 5.02 7.8 3.62 of experiments were conducted in cooperation
IR22 7.6 4.03 8.6 3.52 with the agronomy and chemistry departments
IR24 7.4 4.67 9.0 4.00
IR20 7.6 4.69 9.1 3.64 at the IRRI farm for four consecutive seasons in
C4-63G 7.4 4.70 8.8 3.49 1971 and 1972 to examine the different comRD-3 7.8 4.05 8.8 3.37
Avg 7.5 4.05 8.7 3.61 ponents of variance and covariance in both
tha m iz experimenlprotein content and grain yield. In each experi40 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).

Weed control Protein (%) Yield (t/ha)
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 Fertilized' 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

8Average 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 the large environmental variance as it is to the
conditions in three replications. Eleven varieties small genetic variability. were common throughout the four trials while As expected, the total phenotypic covariance
the rest varied from one trial to another. To between grain yield and protein content was
ensure a wide range of phenotypic variability, large and negative. The separation of this covarithe varieties were chosen primarily for their dance into its genetic and environmental comlarge differences in both protein and grain yield. ponents (including genetic x environment interMoreover, varying levels of nitrogen and plant action) indicated that all of the negative associaspacing, the major cultural practices affecting tion between grain yield and protein content was both characters, were included. Protein content due to the latter component-the genetic covariranged from 6.1 to 15.9 percent and grain yield dance was small and positive. Except for nitrogen from 0.51 to 7.17 t/ha (Table 14).
This series of experiments confirmed previous Table 10. Brown rice protein and grain yield of three
findings that environmental variance of grain rice varieties grown in farmers' fields under different
yield is larger than that of protein content (Table levels of pest and disease control. Laguna, Philippines.
15).It as lea, hoeve, tat he gnetc vri- 1973 dry and wet seasons (Data are averages of 8 to 16 15). It was clear, however, that the genetic va- replications. ance of grain yield is also much larger than that
of protein. In fact, the difference between genetic Protein (%) Yield (t/ha)
variances of grain yield and protein content was Variety season isc ie isc ie
more pronounced than that between environ- control control control control
mental variances. As a result, the ratio of genetic C4-137 Dry 7.6 7.4 5.5 6.2
to environmental variances was more favorable IR20 Wet 8.3 8.2 4.8 6.0
for grain yield (1.0 : 2.8) than it was for protein IR1561-228-3 Wet 8.9 9.0 4.4 5.6 (1.0: 5.2). Thus, the difficulty in the improvement IR20 Wet 9.3 9.3 1.5 5.8
of protein content of rice is not as much due to Ag e envirl v e a 0 i


Table 11. Experimental error of protein content and Groinyield Ct/ho) grain yield estimated from seven series of rice field 7 o *
experiments. IRRI, 1971-1972. DRY SEASON
6 N%#
Coefficient of variation (%) 6

Experiment Degrees of Protein Yield 0 0 % o
no. freedom Dry Wet Dry Wet o 0 0
Year season season season season
4 R8
Y=~-2I.e6+6.72X o.40X2 0
CR2 =0.794*~
1 1971 110 6.3 5.9 8.9 12.4
2 1971 130 5.4 5.9 7.7 9.1 3 1R40
3 1971 120 8.3 7.5 13.6 15.4 (R2 0.748*
4 1972 110 6.6 5.7 8.5 9.4
5 1972 130 7.9 6.5 10.2 9.4 2
6 1972 120 5.4 7.7 11.6 14.9 0t11 I
7 1972 326 7.3 6.9 9.3 8.4 6
Combined 1046 6.9 6.6 9.8 10.7

Table 12. Experimental error$ of grain yield and brown 0
rice protein estimated from agronomytrials, asaffected by the rate of nitrogen application. IRRI, 1971-1973. 3 0

Nitrogen applied Yield Protein Y=-1203+395X-0,23X2
(kg/ha) Mean (t/ha) cv (%) Mean (%) cv (%) 2 R20766 IR480

Dry season 9 =-22.01+507X-024x2
0 4.54 14.7 7.8 7.4 1R2=0.967*l
60 5.77 10.8 8.4 5.7
90 6.35 10.0 8.8 7.5 0
120 6.63 8.7 9.2 6.2 05 6 7 8 9 10 11 12 1314
150 6.55 8.3 9.5 7.4 Brown rice protein (%)
Wet season 4. Relations between protein content and mean grain yield
0 3.52 13.7 7.6 5.9 of IR8 (from 964 observations) and 1R480-5-9 (from 538
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 fertilization, which increased both characters

aData are averages over six trials for grain yield and four trials simultaneously, all other environmental factors, for brown rice protein, each trial consisting of 14 varieties tested with four replications.
yield, depressed protein content and vice versa.
Because of the important implications of these
Table 13. Experimental error (based on 90 degrees of freedom) of grain yield and brown rice protein estimated from agronomy trials, as affected by the time of through breeding, it is necessary that these nitrogen applications. IRRI, 1969-1970. results be confirmed in further studies with the

Time of Yield Protein inclusion of more genotypes and environments.
application Mean (t/ha) cv (%) Mean (%) cv (%)
1969 wet season (60 kg/ha N) YIELD RESPONSE TO NITROGEN
Basal 4.37 14.0 9.4 9.0
Basal + panicle We examined nitrogen response curves taken
initiation 4.54 10.7 9.5 6.5 from 154 fertilizer trials conducted by the
Basal + heading 4.72 10.5 9.7 6.5 agronomy department from 1966 to 1972,
1970 dry season (150 kg/ha N)
Basal 6.00 8.6 8.6 7.1 involvingdifferentvarietiesandselectionsgrown
Basal + panicle under widely different management and environinitiation 6.24 6.9 9.0 6.5 mental conditions. In all trials, at least four
Basal 4 -e-ding+5.75X10.209.6O6.

Basa + eadng .75 0.2 9.6 6.9 nitrogen levels were tested. We found that the


yield response to nitrogen in rice is described Table 14. Range and mean of grain yield and brown rice
appropriately by the quadratic functions: protein of 11 rice varieties end lines tested under varying environments. IRRI. 1971 and 1972 dry and
Y = a + bN + cN2, where Y is grain yield, N is wet seasons.
nitrogen rate, and a, b, c are the regression
parameters. In 1,047 of the 1,304 response curves Designation examined, quadratic response functions accoun- Range Mean Range' Mean
ted for more than 80 percent of the yield vari- R8 2.56-6.73 4.41 7.0-11.1 8.5
ability. The curves that had coefficients of 1324 3.13-6.46 4.27 7.6-10.6 9.0
determination (R2 values) from quadratic fits R20 2.53-7.17 4.39 7.6-11.5 9.1
of less than 80 percent came mostly from trials C4-63G 1.88-5.76 3.89 7.4-12.6 8.9
which involved traditional varieties or which 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
were made in the wet season. For improved Intan 0.51-3.67 1.68 6.1-10.9 8.5
varieties or selections grown in the dry season IR480-5-9 3.00-6.31 4.00 8.2-13.1 10.5
quadratic functions can be expected to give R667-98-1 2.47-6.36 3.98 7.7-12.5 9.6
satisfactory fits about 90 percent of the time;
under other conditions, satisfactory fits can be 'Over 16 environments composed of four test conditions and expected in only 65 to 75 percent of the time. four cropping seasons, each replicated three times.
Several types of nitrogen response curves were
observed (fig. 5): A) Grain yield increased with Ym. (the maximum yield), and Y, (increment nitrogen level, although the yield increment of yield increase based on Nmax rate) were
became less and less as higher nitrogen rates were satisfactory. The use of these parameters in used, and finally reached a point where further distinguishing nitrogen responses in the dry and increase in nitrogen brought about a reduction wet seasons under various conditions is illusin yield. This type of curve, which was the most treated in figure 6. The dry season crops required common, is necessary for estimating economic- a higher nitrogen rate to attain the maximum
ally optimum nitrogen rates. B) The response yield (Nax of 112 kg/ha N for dry season and
was still in the linear phase, that is, grain yield 75 kg/ha N for wet season), while the maximum increased at the same rate throughout the range yield, as well as the returns in terms of kilograms of nitrogen levels used. Optimum nitrogen rate of grain per kilogram of nitrogen, was also
can not be derived from this type of curve since higher (Ymax of 6.6 t/ha in dry season and 4.8 maximum yield has not been reached. To avoid t/ha in wet season; and Y1 of 18.2 kg grain/kg N
getting type B curves, the maximum nitrogen in the dry season and 13.6 kg grain/kg N in the
rate tested in the trial should be sufficiently high. wet season). This indicates clearly that yield C) Yield was reduced as nitrogen rates increased. response to nitrogen application in the dry This type of curve occurred mostly with tradi- season is better than in the wet season. Of the
tional varieties grown in the wet season. various factors examined, the two major ones
To find one or more measures for comparing affecting nitrogen response are crop season and
and describing a large number of nitrogen varietal type. The differences are illustrated in
responses, several parameters were examined. figure 7 for crop season and figure 8 for varietal
Nmsx (the nitrogen rate that maximizes yield), type.

Table 15. Components of variance and covariance of grain yield and protein content of rice.
Degrees Brown rice protein Grain yield Grain yield x protein
Component of
freedom Variance cv (%) Contribution (%) Variance cv (%) Contribution (%) Covariance Contribution (%)
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)





0 50 100 150 200 0 50 100 150 0 50 100 150
Nitrogen applied (kg/ha)
5. Three major types of nitrogen response curves of rice.

SOILHETEOGENITYeach of these plantings, 1R1514A-E597 was SOIL HETEROGENEITY
grown throughout each area.
Planting an area to varieties differing in growth Thedryseason dataindicated some differences duration by more than 10 days increases soil in grain yields from plots planted to the six heterogeneity in the following season (1972 varieties in the previous wet season (Table 16). Annual Report). This year, we evaluated the Yields of 1R1514A-E597 from plots in which effect of growing varieties differing in both IR747B2-6-3 (having the shortest growth duragrowth duration and tillering ability under tion) had been grown previously were the highest, different plant spacings. even though 1R747B2-6-3 had the largest tiller
In the 1972 wet season, IR8, C4-63G, IR478- number. Difference in tillering ability did not 68-2, IR127-80-1, IR1561-228-3, and IR747B2- seem to give appreciable residual effect relative 6-3, were grown under three plant spacings, to growth duration. 10 x 10 cm, 20 x 20 cm, and 30 x 30 cm, in On the other hand, in the wet season trial three replications. In 1973 dry season, IR127- where the four varieties tested not only had a 80-1, IR841-5-1, Ratna, and IR1561-228-3, were longer growth duration but also a smaller range grown at 10 x 10 cm, 20 x 20 cm, and 30 x 30 of growth duration than the six varieties in the cm in I11 replication. In the season following 1972 dry season trial, there was no significant

Freqiexcy M%)
25 XI3
20- R=112
X=75 R=&68
Wet A .
10i gi f p
seasonni w
Y id ofIl1AE9 rmpoin hc

even thoug IR4B-- ha h ags ile

0 50 100 150 200 02 4 6 8 10 03 9 15 212733 39
Nnab kg/ Dho) max (t hat Yi kg grain/ kg n)
6. Frequency distribution of three nitrogen response parameters, based on 564 response curves ofdifferent varieties grown under varying conditions, by crop season. 1966-1972.


Grain yield (t/ha) Grain yield (t/ha)
7 8

6-/ Dry seasonIpoe ait
Y=4.57 +0.036 N -00002 N2 6


44 .
Wet season / %
Y=3.81 +0027 N-00002 N2 Non-improved variety

0 Il
0 50 100 150 200
Nitrogen applied ( kg / ha )
7. Estimated nitrogen response of rice for dry and wet season 0 crops, based on data from 564 response curves of different 6 varieties grown under varying conditions. 1966-1972. WET SEASON

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 2
although average yield reduction was otly about 0.2 t/ha. On the other hand, there was no significant difference between 20 x 20 cm and 30 x 30 cm spacings. 0
0 50 100 150 200
CROPPING 8. Average nitrogen responses for improved and nonimproved varieties based on 195 response curves, by crop Most statistical procedures developed for agri- season. 1966-1972. cultural research are primarily meant for experiments involving single crops. Multiple cropping ments are generally undertaken. Second, large technology, however, requires the simultaneous experimental error can be expected when several testing and evaluation of several crops following crops which differ in plot techniques and cultural a prescribed combination or sequence of plant- requirements are tested together. Third, since ing. Thus, instead of being concerned only with economic data are much more important in the environmental factors surrounding a single crop, evaluation of multiple cropping systems than in multiple cropping research demands a technique single-crop experiments, the experimental proby which many types of crops and crop cedure must conveniently permit measurement
sequences can be tested under varying environ- of economic data. ments. Three major difficulties are encountered To cope with the large number of multi-factor
in multiple cropping experiments. First, since treatments involved in a multiple cropping trial, crop combinations and crop sequences usually we developed a modification of the standard
have large interactions among themselves as well fractional factorial design for a test which was as with environmental factors, multi-factor conducted by the multiple cropping department
experiments involving a large number of treat- in 1973 dry season. The test involved 63 interSTATISTICS 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
1R747B2-6-3 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
IRS41-5-1 11 111 3.16 3.45 3.42
Avgc 3.15 b 3.32 ab 3.37 a

'Days after transplanting. bThree replications. cMeans followed by a common letter are not significantly different at the 5% level. d1 1 replications.

cropping systems (composed of three crops- able size without losing information on some
mung, sweet potato, and peanut-grown singly important interactions.
or intercropped at different durations of overlap Although the measurement of economic data and under seven planting arrangements of corn) may require plot sizes larger than that of agronotested under three fertilizer levels and four weed mic data, replication may not be necessary for control levels. Over 750 treatment combinations achieving the required precision in the former. were possible, but our suggested design consisted Thus more than one plot size should be used in of only 256 treatments, half of which were a trial-larger plots (without replication) for the
replicated while the rest had no replication. The collection of economic and agronomic data, and evaluation of the design showed its potential for smaller plots (with replication) for agronomic reducing the number of treatments to a manage- data.


Pl n tThe grain yield of an early maturing line, P lan t IR747B2, planted year-round at Los Bafios
was highly positively corphysioloy related with solar radiation and negatively correlated
with daily mean temperature during the 25-day period before flowering. The derived formula of climatic productivity index predicts that a combination of high solar radiation and low daily mean temperature will give high yields. O 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. FO Further studies on varietal difference in net assimilation rate indicate that large difference exists only under strong sunlight. OZ 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. F Studies on the biology of S. Maritimus showed that flowering can be induced by cutting the 140-dayold plants, coinciding with the rice harvest. This weed grows at a faster rate than rice. The growth is very sensitive to light intensity.

CLIMTIC NFLENCEON YELDfilled grain percentage is determined at and after CLIMATIC INFLUENCE ON YIELDflowering. Among the yield components measIn past studies, great emphasis was placed on urged, grain number per square meter was most effect of solar radiation on ripening and hence variable, 1,000-grain weight was somewhat vanrice yield. In our analysis of grain yield of IR8, able, and filled-grain percentage was fairly conhowever, grain number per square meter was stant. highly correlated with yield, and there was not Multiple regression analysis indicated that much variation in filled-grain percentage or 81.4 percent of the total variation in yield could 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. 1
In the past, the effect of temperature on grain number has been totally neglected. Controlled environment studies, however, have shown that 8 C0
temperature during panicle development affects grain number (1972 Annual Report). 4 I
To examine climatic influence on yield components and yield, an early maturing line,
IR747B2-6, was planted in the field every 2 Lf area index weeks, giving 26 crops in 1 year from July 1972. 0 Seven crops were excluded from the analysis because of severe lodging and damage by diseases and insects. 6
Growth characteristics of IR747B2-6. 4
IR747B2-6 matures in 96 days from sowing to harvest at Los Bafios throughout the year. It 2 develops 13 leaves on the main culm (fig. 1). 0 Panicle initiation occurs about 20 days before Tillers (no/sq m) flowering. The estimated date for necknode 000 differentiation stage is 25 days before flowering, 800 about 7 to 8 days later than that for mediummaturing varieties. At 10 x 10 cm spacing and 600 with 100 kg/ha N, it develops sufficient leaf area 40o index and enough tillers for maximum yield (1970 Annual Report).
Yield and yield components. Grain yields of 19 0
crops (fig. 2) ranged from 4.6 to 7.1 t/ha. Plant- Total dry wt kg/sq m ings from December through March gave high yields. Grain yields were highly correlated with 1.2 total dry weight (r = 0.856**), indicating that high photosynthetic production was simply 0.8 related to high grain yield. Grain yield of rice can beexpressed: 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 0 20 40 0 80 too
conditions, grain number is determined before ays from seeding
flowering, 1,000-grain weight is determined 1. Growth process of 1R74712-6 planted at 10 x 10 cm partially beforeandpartiallyafterflowering, and spacing with 100 kg/ha N at IRRI.


be explained by N, F, and W. The relative Yield (t/ha)
importance of the three variables, as evaluated 8 from standard partial regression coefficients, was
0.614 for N, 0.212 for F, and 0.345 for W. Thus, C
grain number per square meter is almost twice as important as grain weight and approximately 6 three times as important as filled-grain percentage in estimating yield.
By means of correlation coefficients as well as multiple regression analysis, we computed the percentage contribution of yield components, 4 individually or in combination, to yield. N alone explained 60% of yield variation (Table 1) while the combination of all the yield components 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 0 most important yield component limiting yield N-A4-M--J--J---A I Sin this experiment.Harvest
inths xprien.2. Grain yield s of I R747B12-6 plIanted every 2 weeks. Shaded
Climatic influence on yield. To examine effects crops were damaged by lodging, insects, and diseases. IRRI, of solar radiation and temperature on yield and 1972 to 1973. yield components, the growth of the IR747 line was divided into three 25-day periods: 1) trans- climatic productivity index was 0.888**. planting to necknode differentiation, 2) neck- Using 18.1 g for 1,000-grain weight and 86 node differentiation to flowering, 3) flowering to percent filled grains (the mean values of the 19 maturity. crops in this experiment), we can estimate grain
We found a high correlation between grain yield of the IR747 line: Y = S2 (278-7.07 T2). number per square meter (N) and solar radiation 0.86-18.1.10--. Since the computed yield is during period 2 (S2) and temperature during expressed in terms of solar radiation and tempperiod 2 (T2) (fig. 3). This relationship can be erature, it is called climatic productivity index. written N/S2 = f(T) = 278-7.07 T2. This This index is highly correlated with actually
equation implies that grain number per square measured yield (fig. 4) which implies that yield meter is positively correlated with solar radiation of the IR747 line at Los Bafios is positively corduring period 2, that is, 25 days before flowering, related with daily solar radiation and negatively and negatively with daily mean temperature with daily mean temperature during the 25-day during the same period. The negative correlation between grain number and temperature agrees well with the results of controlled environment Table 1. Contribution of each yield component to grain studies (1972 Annual Report). The above yield.
equation is rewritten N = f(S, T) = S2 (278- Vble Contribution to total
7.07 T2). This implies that grain number of the variationinyield_(%)
IR747 line can be estimated in terms of solar N 60.2
radiation and temperature. Since grain number F 21.2
N and F 75.7
determines potential grain yield, the proposed N and W 78.5
function, f(S, 7), is called potential climatic N and F and W 81.4
productivity index. The correlation coefficient N = grain number per square meter; F = filled grain percenbetween measured grain number and potential tage; W = 1,000 grain weight.


N/S2 Grain yield (t/ho)
120 8

Sy =13+0.81 X 110 -r 0901
7 0

0 *

90 0 0

70 -0
0 2 0 9

1 278 -707 XX
r =0.829** 0
70 4

0 4 5 6 7 8
60_ ~Climatic productivity index ( t/hao)
0T4, 1 4. Grain yield in relation to climatic productive ity index.
0 24 25 26 27 28 29
Temperature (*0)
3. Grain number per square meter (N) and solar radiation
(S2) in relation to daily mean temperature during the period differentiation to flowering. Solar radiation of 25 days before flowering. during the ripening period has a slight effect on
ripening, but less than previously believed. This period before flowering. We also obtained a high conclusion seems to be valid when daily solar correlation between grain yield and solar radia- radiation is more than 300 Cal- cm2 .day-'. tion during the ripening period (r = 0.834**). In our experiment, the size of sink (grain Although many workers have reached the same number) was most limiting to grain yield, and result, we found that solar radiation during the hence solar radiation and temperature during ripening period is highly correlated also with the period when the sink size is determined are potential climatic productivity index in our the strongest influences on grain yield at Los experiment at Los Bafios (r = 0.831**). Thus Baios. the high correlation between yield and solar A combination of high solar radiation and
radiation during ripening period may be only low temperature gives high grain yields (fig. 6). superficial. The concept of climatic productivity index proTo examine direct effect of solar radiation on videos a way to assess relative rice productivity yield, the correlation coefficient was computed for different localities under different climatic for ripening grade and solar radiation during environments. 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 Leaf resistance and moisture stress. Under most correlated with solar radiation during ripening conditions the major path of water loss by the period (fig. 5). plant is stomatal transpiration. Stomatal transThe evidence seems to indicate that grain piration is controlled by stomatal aperture which number is the most important factor limiting is in turn regulated by light and moisture supply. grain yield, and it is highly correlated with solar To study relationships between leaf resistance radiation and temperature during the 25-day (combined resistance of stomates and cuticle), period before flowering, that is, from necknode moisture stress, and solar radiation, IR5 plants


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

Field moisture capacity Dry wt (g/pot) Tillers Plant ht Leaf area
during treatment (%) Leaf Culm Root Total (no.) (cm) (sq cm)
Flooded 21.1 29.9 18.2 69.2 69 84 6200
70 14.7 22.4 8.4 45.5 53 72 4200
50 10.6 16.6 5.0 32.2 49 66 2700
35 6.3 8.6 2.5 17.4 37 60 1700

'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 2.5 to 5.0 s/cm. This implies that the rice plants
conditions at near-field capacity for 35 days. The grown in the flooded soil had little or no moisture plants grown under upland conditions were then stress, and hence the stomates were open during
subjected to one of three water regimes-70 per- the daytime. Under such conditions, the plants cent, 50 percent, or 35 percent of field moisture may use solar radiation for photosynthesis at capacity-for 3 weeks. Plants under flooded maximum efficiency. The plants grown under
conditions were allowed to continue to grow upland water regimes showed similar diurnal
normally for the same period. changes in leaf resistance on very cloudy days.
The 3-week moisture stress greatly affected On sunny days, however, leaf resistance values
leaf area and dry weight (Table 2). Plant height of those plants started rising rapidly in the afterand tiller number were less affected. noon or even in the morning depending on
On cloudy days, visible symptoms of moisture weather conditions. These measurements show stress occurred only on plants grown at 35 per- that even under the same soil water regime, 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 500 Cal* cm 2day
on cloudy and sunny days during the stress 7
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 6 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
Y = 13.1+ 0.00656 X
1T r = 0.480*
16 0
0300 350 400 450 500 550 0 25 27 29
Solar radiation (cal. cm2 day1) Temperature
5. Ripening grade in relation to solar radiation during 6. Climatic productivity index in relation to solar radiation ripening period. Ripening grade is the product of filled-grain and daily mean temperature during the period of 25 days percentage and 1,000-grain weight. before flowering.


Leaf resistance (s /cm)

60 -70% of FMC I


I I /
Flooded I#

s I
0 ~II /

0400 0800 1200 1600 0400 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 through stomates on leaves, and transpiration stress on sunny days than on cloudy days. Thus, should be affected by increased leaf resistance under conditions of moisture stress, a high level under moisture stress. To study how internal of solar radiation will induce stomatal closure moisture stress affects photosynthesis of rice during the daytime, and hence radiation will not leaves, we grew IR5 plants in pots for 34 days be used by the plant for photosynthesis. There- with sufficient water and then induced moisture fore, relationship between solar radiation and stress by withholding water from the pots. Leaf plant growth in flooded conditions should be resistance was taken as an indication of internal quite different from the relationship under moist- moisture stress and measured with a diffusive ure stress. Under flooded conditions, increasing porometer. The measured resistance values were amounts of incident solar radiation will increase multiplied by 1.71 to obtain the resistance to plant growth. Under moisture stress, however, carbon dioxide. high solar radiation will not have a favorable Both the maximum photosynthetic rate and effect on plant growth. Based on theoretical the saturation light intensity varied with varying consideration of the light-photosynthesis curve, leaf resistance (fig. 8) with increased leaf resistit is more likely that moderate incident solar dance, the photosynthetic rates reached maxiradiation is more favorable for plant growth than mums at low light intensities and the maximums high solar radiation. Thus, upland rice culture were lower than those with less leaf resistance. in partial shade such as under coconut trees This implies that high solar radiation is not fully merits more attention. used for photosynthesis under moisture stress.
Photosynthesis under moisture stress. Since In other words, a large proportion of strong leaf resistance increases under moisture stress, sunlight is wasted under moisture stress. Strong photosynthesis, or intake of Cs2 which occurs sunlight may even have adverse effects on rice


growth by raising leaf temperature and by Gross photosynthetic rate
inducing stomatal closure early in the day. (mg 002 dm 2* h )
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 2
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 0
resistance. Under severe moisture stress, as 0 20 40 60 80
indicated by high leaf resistance, degree of leaf Light intensity kis)
8. Photosynthetic rates of rice leaves under moisture stress rolling varied: 81B25 rolled more than IR20, at different light intensities (r. = resistance).
MI-48 rolled more than IR5.
If different degrees of leaf rolling occurs at a around flowering time, which induces high similar leaf resistance as we observed in this sterility, is the most critical for rice yield.
experiment, leaf rolling could be regarded as a desirable character for drought-resistant varieties. Leaf rolling should decrease transpiration loss, thus conserving moisture in the soil. Field assessment. To determine varietal differPlant changes induced by moisture stress. A fences in drought resistance under the field
series of physiological events occurs when the conditions, we grew 20 varieties at the IRRI farm
rice plant is subjected to moisture stress (Table under three water regimes. The degree of mois4). Except for sterility, all characters are highly ture stress was varied by changing frequency of dynamic and hence reversible. Once moisture irrigation. Plant height under moisture stress
stress is relieved, most characters return to relative to that under no moisture stress was
normal conditions. Therefore, moisture stress Table 4. Physiological and morphological changes Table 3. Leaf rolling and leaf resistance of four varieties inducedbymoisturestress. grown in pots. Without With
Water Leaf Leaf Feature moisture moisture
Variety withheld resistance rolling stress stress
(days) (s/cm) Visible features
Pot A Plant height Normal Reduced
IR20 1 2.5 None Tiller Normal Reduced
2 2.8 None Leaf area Normal Reduced
3 61.0 Half Lest rolling No Yes
818B25 1 2.8 Slight Sterility Low High
2 3.9 Slight Non-visible features
3 80.0 Complete Stomates Open Closed
Pot B Major path Stomatal Cuticular
IR5 1 3.4 None of water loss transpiration transpiration
2 3.9 None Leaf water potential High Low
3 75.0 Slight Lest temperature Low High
Ml-48 1 5.1 None Heat tolerance Low High
2 6.9 None Photosynthesis High Low
3 79.0 Complete Proline content Low High


Table 5. Drought resistance of 20 varieties as assessed resistance. The cuticular resistance values of by plant height reduction under moisture stress in mesophytes, to which most crop species belong, field, IR RI. 1973 dry season.
fiel, 11113, 173 ry saso. come in between the above two. Little attention
Plant ht (cm)* Relative plant htb has been paid to varietal difference in cuticular
Designation No Moderate Severe Mean resistance for a given species. Since rice grows
stress stress stress under diverse water regimes from upland to
E425 75 79 77 78 flooded conditions, a large variation in cuticular
Miltex 86 77 68 73
M1 -48 107 72 69 71
Jappeni Tungkungo 92 68 73 71 difference might be related in part to drought
OS4 89 68 67 68 resistance of rice varieties.
Palawan 97 69 66 68 Measuring cuticular resistance of rice leaves
Dular 96 70 61 66
Rikuto Norin 21 85 74 57 66 is difficult because the rice plant has stomates on
P1215936 55 74 58 66 both sides of its leaves. We measured cuticular
Azucena 105 67 61 64 resistance with a diffusive porometer in the dark
Azmil 88 73 54 64
IR5 62 70 56 63 and when the plant was fully turgid.
R127-80-1 84 69 52 61 The cuticular resistance values of 35 rice van811B25 88 65 54 60 ties varied from 30 to 68 s/cm (Table 6). Some
IR442-2-58 66 60 57 59
NARB 96 61 52 57 varieties that perform well under upland condi1R8 62 61 47 54 tons showed high cuticular resistance values.
IR1529-680-3 65 60 47 These were Azmil, Rikuto Nor 21, several
IR841-67-1 62 57 48 53
IR20 64 57 44 51 RP-79 lines, Azucena, M1-48, R442-2-58, Bala,
aMeasured 41 days after sowing. bTaking plant height at no ete suc h s P an me and vSi moisture stress as 100.
had a low cuticular resistance. Among these
varieties, Palawan and 0S4 are known to have
taken as a measure of drought resistance. Plant longer and more branched roots. It is not sunheight is one of the plant characters most uprising that more than two mechanisms confer
sensitive to moisture stress. drought resistance.
Most upland varieties seemed to be more Sorghum and corn are known to be much more
resistant to drought than lowland varieties resistant to drought than rice. Indeed, sorghum
(Table 5). Among lowland varieties, IR5 can be and corn have higher cuticular resistance values regarded as relatively resistant and IR20, as very (Table 6). Their cuticular transpiration is only susceptible. These results seem to agree well with one-half to one-fourth that of rice varieties. those obtained by the varietal improvement The measurements of the cuticular resistance
department. Some physiological characters, of rice varieties indicate that there is a considersuch as heat tolerance and quick closure of able variation in cuticular resistance of rice
stomates in response to moisture stress, confirm leaves among varieties, and high cuticular that E425, MI-48, OS4, and Palawan are resistance accounts in part for the resistance of
resistant and IR20 is susceptible (1972 Annual rice varieties to drought. It should be desirable Report). to combine cuticular resistance with long and
Cuticular resistance. High cuticular resistance well-branched roots in one variety.
of the leaf surface is a desirable characteristic for Proline assay. The proline content of plant drought resistance because when stomates are tissues increases when plants are subjected to closed under moisture stress, cuticular trans- moisture stress. Therefore, increase in proline piration becomes the major path of water loss by content can be an indication of physiological the plant. Significant differences exist in cuticular dryness. In barley, increase in proline content resistance among plant species. In general, in leaf tissues is positively correlated with aquatic species which live in water have small drought resistance. resistance values while xerophytic species that In a preliminary study to see if proline assay are adapted to dry climates have high values of can be used for screening drought-resistant rice


Table 6. Cuticular resistance of 35 rice varieties, and solution specifies the water potential of the sorghum and corn. system, a measure of moisture stress. Proline
Cuticular content in leaf segments did not increase down Variety resistance to 2 bars but below that proline content in(s/cm) creased sharply with decreasing water potential
Sorghum (Cosor 3) 116 (fig. 9).
Corn (Early Thai composite) 112
Azmil 68
Rikuto Norin 21 66
RP-79-1 9 66 Varietal difference in net assimilation rate. VanRP-79-14 63
RP-79-13 60 etal differences in the net assimilation rate of 12
RP-79-16 60 varieties selected from 313 varieties (1972 Annual
Azucena 60 Report) were further tested under and low
RP-79-23 57 solar radiation (Table 7). Varietal differences
Ml-48 56 were clearer under high solar radiation than
IR442-2-58 54 under low solar radiation. CP231 and Molaga
Bala 51
Sigadis 49 consistently net assimiTaichung Native 1 49 nation rates under both high and low solar
IR5 48 radiation. BJ1 vigorously
N-22 47
RP-8-8 47 a high net assimilation rate. High net assimilaIR841-67-1 47 tion rates were closely correlated with nitrogen
RP-7-2 44 content per unit leaf area. The effect of solar
1131529-680-3 43
Ri 529-628-3 43 radiation on specific leaf weight was also very
R1561 -228-3 43
JappeniTungkungo 42 clear. Specific leaf weight became much smaller
IR26 41 under a low solar radiation than under a high
IR38 37
1B283 solar radiation. In other words, the leaves be81B25 37
1R1541-76-3 36 came much thinner which, in turn, was corIR24 35 related with lower net assimilation rate under a
PI-215936 35
Palawan 33
IR127-80-1 33
E425 33
E425 33 Praline content (Akg/g fresh wt
IR20 32
Dular 30
Miltex 30
054 30 '300

varieties, we examined increase in proline content in rice leaves in response to moisture stressP We found that proline content in leaves of intact plants (sR747hy2-6) increased from 50 pg/g fresh weight without moisture stress to about 7,000 uglg under severe moisture stress.
Technically, it is difficult to subject many 100 intact plants to the same degree of moisture stress at one time. To simplify the technique of stress induction we examined use of leaf segments. Rice leaves were cut into 1-cm segments th
and 0.5 g of the leaf segments was placed in a 0 4 8 12 M 16
a high nettinin nutientsoluiWafer potenil (bars
9. Accumulation of proline in rice leaf segments when
polyethylene glycol for about 24 hours. The floating in polyethylene glycol solutions of different water
amount of polyethylene glycol added to nutrient potentials.


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.
At high solar radiations At low solar radiationb
(mg. cm-2. day-') (mg/dm2) (mg/cm2) (mg cm-2 day-) (mg/dm2) (mg/cm2)
CP231 2.00 24 4.6 0.94 16 3.1
Molaga Samba G18 1.96 20 3.7 .97 13 2.7
BJ1 1.76 20 3.9 .76 14 2.6
Siam 1.74 20 3.7 .80 14 2.8
IR747B2 1.55 19 3.4 .79 12 2.6
MTV7 1.50 17 3.2 .78 14 2.7
Gend Jah Banten 1.44 19 3.6 .86 14 2.9
Zenith 1.44 19 3.3 .87 14 2.6
IR5 1.42 18 3.1 .84 13 2.4
Sigadis 1.40 16 3.0 .77 12 2.4
0. glaberrima* (Acc. 100932) 1.38 16 3.2 .82 12 2.4
0. glaberrimal (Acc. 100989) 1.30 14 2.9 .71 10 2.2
1475 cal cm-2. day-,. b284 cal cm-2 -day'.

Nitrogen nutrition and stomatal resistance. rate of a rice leaf even after it has been fully Nitrogen application affects photosynthesis by developed. increasing leaf area and maintaining high photo- Soil carbon dioxideflux and rice photosynthesis. synthetic rate per unit leaf area. To study the In field photosynthesis, the atmosphere and the second function of nitrogen, we grew IR8 in soil are the source of CO, We estimated the culture solution at a low and a high nitrogen contribution of soil C02 to the photosynthesis concentration. We measured photosynthetic of rice when the field was kept flooded and when
rate, specific leaf weight, nitrogen content per it was drained. unit leaf area, and leaf area. We also measured Soil CO2 flux was increased by drainage (Table changes in stomatal resistance as affected by 9). Estimated contribution Of Soil CO2 to gross nitrogen nutrition. Specific leaf weight of fully photosynthesis was 5 percent for the flooded developed leaves was not affected by nitrogen plots and 7 percent for the drained plots. The supply (Table 8). Nitrogen supply changed effect of drainage may in part account for the
nitrogen content per unit leaf area, which in turn "mid-season drainage" effect on rice yield. The was closely correlated with photosynthetic rate. contribution Of Soil C02 could be greater when
Using the second leaf, we found that stomatal a soil is higher in organic matter content or when resistance of the leaf was not affected by nitrogen crop growth rate is smaller on cloudy days. The supply. This suggests that photosynthetic rate results of this experiment along with other of young rice leaves is simply related to nitrogen information indicate that the atmosphere is the content per unit leaf area, and not to either most important source Of C02 for photosynspecific leaf weight or stomatal control. With thesis of the rice plant, Soil CO2 released into the fourth leaf, however, low nitrogen supply atmosphere is of secondary importance, and decreased nitrogen content per leaf area, but C02 absorbed by roots is the least important. increased stomatal resistance. High nitrogen
supply had reverse effects. Stomatal behavior in
rice leaves apparently is partly controlled by NUTRITIONAL DISORDERS nitrogen nutrition. Thus, in rice, nitrogen content per unit leaf area, is the most useful para- Zinc deficiency or sulfur deficiency may be meter relating to photosynthetic rate. This induced by continuous and intensive rice cropexperiment demonstrated that nitrogen nutri- ping in a field. Since different nitrogen fertilizers tion has a pronounced effect on photosynthetic have different chemical compositions, they may


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
Treatment8 (mg CO2 dm -2 h-') (s/cm) (mg/cm2) (mg/dm)
(ppmN) 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- land varieties and found that the upland vanency or sulfur deficiency or other problems. ties have certain characteristics distinct from
To test effects of three nitrogen fertilizers, those of lowland varieties (Table 11). Whether ammonium sulfate, ammonium chloride, and these characteristics are necessary for drought
urea, on yield, total dry matter production, and tolerance and compatible with requirements possible nutritional problems, we set up a long- for high grain yields must be evaluated in detail. term field experiment at the IRRI farm. Data on The answers may lead to a better understanding total dry weight as well as grain yield were col- of what the ideal plant type for upland conlected to provide a realistic measure of photo- editions is. synthetic production. Plant height at harvest. The upland group was
Grain yield ranged from about 19 to 24 tons about 36 cm taller than the lowland group. The
per year while total dry matter production height of the upland rice varieties makes them
ranged from about 46 to 51 tons per year (Table susceptible to lodging although lodging is not 10). Ammonium sulfate produced slightly higher serious under upland conditions. Tall varieties,
total dry matter and grain yield than ammonium however, may be better able to compete with
chloride or urea. But none of the crops so far had weeds, an important problem in upland culture. any visible indication of nutritional problems. With the use of herbicides in modern agriculture, however, this advantage may no longer be so

UPLANDgreat. It is also possible that among the droughtUPLAN RICEresistant types, the tall varieties have higher grain Characteristics of upland rice. The differences yields.
between upland and lowland varieties and the Tiller number. The upland varieties tested
value of these differences for upland conditions tended to have fewer tillers than the lowland must be understood in order to improve upland varieties. Some workers have recommended
varieties. We studied nine upland and nine low- therefore that the tiller number of the upland

Table 9. Carbon balance between rice photosynthesis and soil COh flux.
Rate (g CH. m2 t dayo') Estimated contribution (%) ofoilCo, to
Soil condition Net dry matter Gross Daytime Net dry matter Gross
production photosynthesis soil Cog flux production photosynthesis
Flooded 22 36 2.0 9 5
Drained 26 44 3.2 12 7


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

Crop Month Variety Yield (t/ha) Total dry wt (t/ha)
no. planted Ammonium Ammonium Urea Ammonium Ammonium Urea
sulfate chloride sulfate chloride
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 1R1561-228-3 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
5 January 188 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 the transpiring surface of a plant, the more water
should be carefully studied since low tiller that is lost and the greater the effect of moisture
number may have a definite advantage when stress on the plant. A large leaf area, however,
water stress is severe. does not necessarily mean a high transpiration
Leaf characters. Upland varieties have fewer rate per plant since the plant may have other leaves per plant than the lowland varieties, a ways to reduce transpiration or increase waterconsequence of fewer tillers per plant. Upland absorbing capacity. varieties also have bigger and thicker leaves than An experiment was set up to examine leaf the lowland varieties. The big leaves possibly area in relation to plant damage when moisture indicate that more photosynthate is available per stress is imposed. Ml-48, a tall, low-tillering tiller of the upland variety, accounting for the upland variety, and IR442-2-58, a short, highheavier tiller, thicker culm, and taller plant. tillering lowland variety which has shown
The reduction in weight of leaves 2 hours after reasonably high yields under upland conditions, detachment showed that the upland varieties were used. The leaf area of one set of plants was
lose moderately less weight than the lowland reduced by 20 percent by removing all lower
varieties. This indicates that upland varieties blades. In another set, leaf area was varied by have better control of transpiration. planting four seeds per pot instead of only one
From the few characters measured it is appar- seed per pot. Watering of the plants was stopped ent that the upland varieties have definite for 9 days at 40 days after sowing.
characters which distinguish them from the low- Plants in which the leaf area was reduced by
land varieties. These and other characters should cutting showed moisture stress symptoms much be evaluated carefully in terms of their contribu- later than the intact plants. This is mainly the tion to drought tolerance and grain yield. result of small transpiring surface. Moisture
Leaf area and drought resistance. Leaf area may stress reduced the leaf area of the IR442-2-58 be an important aspect of drought resistance in line more than that of Ml-48 (Table 12). With the existing upland rice varieties. The greater no stress (control), R442-2-58 plants whose

Table 11. Differences between upland and lowland rice varieties.

Specific leaf wt Reduction in fresh
Variety Plant ht (cm) Tillers (no./hill) Leves (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 18.2 14.0-23.5 84 70-101 24 19-31 2.67 2.2-3.0 20.7 17.2-23.5
Difference 36- -9.6r -eu -44ce 21 0.38 -3.2v a


lower blades were removed had a significantly Table 12. Moisture stress and reduction in leaf area of greater leaf area than comparably treated M1-48 plants with intact leaves and plants with 20 percent plants, but moisture stress made the leaf areas reductioninleafarea. the same. Moisture stress also reduced the leaf Leaf Leaf areaa (sq cm/hill) Reduction
area of intact IR442-2-58 plants more than that treatment Moisture stress Control M of IR442-2-58 plants that had the lower blades Ml-48
removed. Intact 1410 2780 49
Thus a large leaf area has little advantage for 20% removed 1810 2430 26
plants subjected to moisture stress because Intact 9840 4300 77
moisture stress reduces the leaf area to a level 20% removed 1700 4120 59
comparable to that of varieties that start with 'LSD (5%) = 540. much smaller leaf areas.
Leaf area, especially under field conditions,
can also be changed through the seeding rate. are needed. Plant density is usually critical under An increase in tiller number per unit area with upland conditions, however. Since soil moisture higher seeding rate usually increases the leaf is the main limiting factor under upland condiarea. The effect of seeding rate on drought tons, plant density must be adjusted to available resistance was tested using one and four seeds moisture and not to available solar radiation and per pot. With no stress, sowing four seeds per nutrients for high yield nor for control of weeds. pot was definitely superior to one seed per pot, Increasing the tiller number or leaf area for as measured by dry matter production at field greater yield potential will make the upland. capacity. When moisture stress was imposed, varieties more susceptible to drought unless the however, plants in the pots with four seeds increase is accompanied by other factors that showed the symptoms of moisture stress earlier will increase the variety's water-use efficiency or than the plants in the pots planted with only one resistance to drought. seed. Compared with the corresponding control,
the decrease in dry matter production was 59
percent in the four-seed pots and 45 percent in Effect of planting methods. Previous studies the one-seed pots. After the moisture stress showed that rice seeds buried in the paddy soil period, the difference in total dry weight be- can germinate and grow as volunteer rice plants tweenoneandfourseedsperpotwasinsignificant. even after three cropping seasons. Our data
For the two plant densities, the decrease in showed, however, that volunteer rice will not be leaf area as a result of the moisture stress was a problem in transplanted rice provided the higher in the IR442-2-58 line (58o) than in volunteer variety and the planted variety do not M1-48 (46 o). Although IR442-2-58 plants had have the same plant type and growth duration. a larger leaf area before the moisture stress With the mechanization of rice culture, broadtreatment, afterwards it became smaller than cast and drilled sowing may become increasingly that of MI-48. The difference is greater when widespread. Under these conditions the probbased on leaf area per tiller. lems of volunteer rice may be serious. A field
Moisture stress decreased the tiller number trial indicated that the competitive character of per pot regardless of the number of the seedlings volunteer rice is not enhanced by drill-planting per pot or the variety used. But the four-seed (0.8 volunteer plants/sq m) as compared with the pots had a relatively larger reduction than the transplanted method (0.9 plants/sq i). Both one-seed pots. planting methods resulted in less volunteer rice
Under moisture stress, IR442-2-58 had more than the uncropped plot (2.8 plants/sq i). The tillers per unit area than MI-48, but for drought volunteer rice plants growing in the cropped tolerance high tillering capacity or a high seeding plots had few tillers compared with those growrate may actually be a disadvantage. Upland ing in the uncropped plots. The volunteer plants varieties generally have low tiller number. To suffered from competition of the planted rice increase grain yields, medium-tillering varieties crop.


Germination M00 Table 13. Germination of intact and dlehulled H4 seeds
100 IR 4(stored for 49 days after harvest) in air or nitrogen gas.
Seed Gas Germination( %
Naua 0Dehulled Air 96 a
N 65 b
80 /Intact Air 90a
4 Total N 10 c

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

surface. On the other hand, 1R8 seeds will
germinate even when deeply buried and no 40 possibility of elongating to the soil surface
404 1 exists. Since the viability of IR8 seeds in sub!!
Nitrogen merged soil is lower than that of H4, IR8 will
o give a lower percentage of volunteer rice in
20 -succeeding crops.
The role of the hull in inhibiting the germination of H4 was studied by germinating dehulled seeds in nitrogen gas. Dehulling increased the 0 111 germination percentage in nitrogen, but the
0 14 28 0 14 28 42 germination was not as high as in air (Table 13).
Days after harvest A reaction of the nitrogen with the hull definitely
10. Germination of I R8 and H-4 seeds incubated in natural air or nitrogen gas (total is germination in nitrogen plus inhibits germination. Probably, nitrogen has a germination in air after removal from nitrogen). separate reaction in the seed causing inhibition even when the seed is dehulled.
Thus in transplanted and drilled sowings, the The main difference between these two vannumber of volunteer plants is relatively small ties seems to be in the hulls and their ability to
and should not pose a serious problem for remain dormant when oxygen concentration is
farmers except those producing certified seed. low.
Survival of seeds buried in flooded soil. Previous
experiments showed that IR8 and H4 seeds Table 14. Flood damage to newly transplanted rice
remain viable even after 1 year in submerged (IR253-16.1) and rice at booting stage (C4-137).
soil, but H4 has a higher proportion of viable seeds. An experiment was conducted to find out urationco Degree of Survival Tillers
if IR8 and H4 have different oxygen require- (days)
ments. In nitrogen gas, no freshly harvested IR8 1R253- 16-1 (seedling stage)
seeds germinated (fig. 10). Twenty-eight days 21 total 1 1.2
after harvest, however, the dormancy of IR8 20 total 50 2.5
16 total 90 5.7
apparently was lost and the germination in 7 total 98 8.2
nitrogen was more than 60 percent. That is 2 leaf tips 100 20.2
nevertheless a low level compared with the above water
C4- 137 (booting stage)
control. 23 total 30 1.2
Germination of H4 was low in the nitrogen 20 total 90 2-5
gas regardless of the state of dormancy of the 20 leaf tips 100 3.7
above water
seeds. H4 definitely needs a higher oxygen con- 15 leaf tips 100 14.0
centration to germinate. That could mean that above water
H4 seeds buried in the soil will not germinate 15 most leaves 100 15.0
Tabe l.Grmiatioe ofiater ddbledH ed

and eventually die unless brought to the soil orove nitroge