APPROPRIATE TECHNOLOGIES FOR DEVELOPMENT
New CrOP Production
INFORMATION COLLECTION & EXCHANGE REPRINT R-6
INFORMATION COLLELMION & EXAG
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CROP PRODUCTION HANDBOOK
CROP PRODUCTION HANDBOOK
GUIDE FOR FIELD CROPS
IN THE TROPICS
AND THE SUBTROPICS By:
Information Collection and Exchange Office of Training and Program Support
Information Collection and Exchange
The New Crop Production Handbook combines the best of two previous ICE Reprints, Crop Production Handbook and Guide for Field Crops in the Tropics and Subtropics.
Guide for Field Crops in the Tropics and Subtropics was developed by the Office of Agriculture, Technical Assistance Bureau, Agency for International Development. The first three chapters of that manual are incorporated here as general introductory chapters.
The-Crop Production Handbook was developed under contract by the staff of Development and Resources Corporation specifically for the Peace Corps. This revised manual contains those chapters of the Handbook which are dedicated to the production of specific crops.
The New Crop Production Handbook also includes references, conversion factors, an appendix and a glossary of terms taken from the original manuals.
TABLE OF CONTENTS
INTRODUCTION . SECTION I .
I - SOILS.
Introduction . Soil Formation . w . Soil Classification . Soil - Water Relationships . Physical Properties . Soil Reaction . Soil Fer.tility . Application of Fertilizers . Soil Organisms . . .q . Soil Conservation .
II - PLANTS
Introduction . Classification of Plants Coloration in Plants . How Plants Grow . Leaves . Stems . Roots . Flowers . Seeds . . Vegetative Reproduction . Weed Control . Plant Diseases .
. i .
. . V . W . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
o . . . . o . . . . . . . . . . . . . . . . . . . .
o . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
o . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . ; o . .
. . . . . . . . . . o . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . o o . . . . . . . . .
III - ENTOMOLOGY
Introduction . .
Insect Classification and Structure . Metamorphosis . Insect Control . w . o . Common Crop Insect Identification . -
81 101 113 125 131 137
143 151 157 165 173 183 191 199 207
65 66 67 68 71
SECTION II - SPECIFIC CROPS . .
IV - CEREAL CROPS
Rice . Maize . w . Sorghum . - *Millet . Wheat . ; . I . Barley .
V - FOOD GRAIN LEGUMES
Field Beans . Cowpeas . Chickpeas . Lentils . Broadbeans . i . Mungbeans . Pigeon Peas . Field Peas . Secondary Food Legumes .
CHAPTER VI - OIL SEED CROPS
A. Groundnuts . 215 B. Soybeans . 225 C. Sesame . . 233 D. Sunflower . 241 E. Safflower . 251 F. Castorbean . W. 257
CHAPTER VII - STARCHY CROPS
A. Banana and Plantain . 263 B. Taro and Yautia . 275 C. Cassava . 279 D. Yams . 285 E. Sweet Potatoes . 291 F. Potatoes . 297 G. Onions . 303
CHAPTER VIII - FIBER CROPS
A. Cotton, for Lint and Seed . 309 B. Jute . 319 C. Kenaf . 323 D. Ramie . 331 E. Abaca, Manila Hemp . 335 F. Sisal, Henequen and Related Hard Fibers . 341
CHAPTER IX - SPECIAL CROPS
A. Pyrethrum . 347 B. Tobacco . 353
SELECTED REFERENCES . 367
CONVERSION FACTORS . 371
A. Approximate Number of Plants per Acre . 373 B. Crop Planting Table . 374 C. Plant Nutrients for Deficiency Symptoms . 375 D. Weight of Substances . . 379
E. Useful Weights for Crop Production .::::::: . 380
GLOSSARY OF TERMS .
CHAPTER I - SOILS
Soil is a living body covering the surface of the earth consisting of weathered rocks or mineral matter, organic matter, water, air and living organisms. Soil is the medium for the growth of all food and fodder crops. Soil offers mechanical support, air, water and essential plant food nutrients for plant growth. It consists of approximately 50 percent solids, 25 percent air, and 25 percent water. A large population of living organisms is dispersed throughout the entire mass.
Every soil has a characteristic morphology or profile in the field. A succession of layers extend down into loose weathered rock. These layers are known as horizons. The horizons differ in one or more properties such as color, texture, structure, consistency, porosity and reaction. A vertical section exposing the horizons is called'a soil profile.
B. SOIL FORMATION
The major steps in the formation of soils are accumulation of soil parent materials and differentiation of horizons in the profile.
The weathering of rocks provides soil parent material. Solid rocks disintegrate slowly under the influence of climate. Temperatures, rainfall and air movement all tend to weaken the rock structure. The minerals in the rocks react with water and air that enter through tiny cracks and crevices. Changes in the minerals then se.t up stresses which further weaken the rock structure. The final effect of these forces is to break a rock into small pieces. Gradually rocks disintegrate and decay. The loose and weathered rock materials may then become soil parent materials. A mantle of weathered rock known as the regolith now blankets the land surface. This regolith has been formed in some places by disintegration and decomposition of rocks on the spot. In many more places, it has been moved about by water, wind,' or ice. The composition and thickness are important to soil formation. The nature of the original rock and the stage of weathering of the regolith affect the fertility and water relationships of soils.
Plants soon begin to gain a foothold in this new soil. Sometimes they begin growing on rock before it has completely disintegrated. Many simple plant forms such as lichens and funit, begin growing. Larger and more complex plants soon follow. Small animals then join the biological community in this infant soil. As these organisms grow and die, their bodies are left on and in the regolith. Parts of dead plants fall to the surface. Roots are left
within the weathering rock mass. The addition and decay of organic matter gradually change the character and appearance of the surface layer of this regolith or new soil. It begins to differ from the deeper layers. It thus becomes what is known as the "A" horizon marking the first stage of the differentiation of horizons.
Horizons are formed in soil profiles because of gains, losses and
alterations. Organic matter is usually added to the surface layer in greater quantities than to deeper ones. Gains in organic matter are an early step in the differentiation of horizons in most soils. Water also makes possible the differentiation of soil horizons. Water may leach some of the elements and minerals from the top of the "A" horizon into lower horizons. This water usually comes from falling rain. Once in the soil, the water dissolves minute quantities of mineral and organic matter. These dissolved substances move with the water.
The five major factors in soil formation are:
1. Climate. Perhaps the greatest influence upon soil development
is climate. Climate can be divided into two categories -- temperature and precipitation. With an increase in temperature,
chemical reactions increase. The rate of weathering, therefore, increases with increasing temperature. The amount and type of precipitation greatly influences the acidity or alkalinity of a soil.
In general, acid soils occur in regions where the annual rainfall is greater than 15 - 20 inches pei year. It is important to know if the rainfall is seasonal or distributed throughout the year. It
is also important to know if the rainfall occurs as a general mist
or a deluge. Because climate is so important to soil formation, the broad soil regions of the world tend to follow the distribution
2. Organic Material. Plants,. animals, insects, bacteria, and fungi
are important in soil formation. Gains in organic matter in the
soil, gains or losses in plant nutrients and variationsin structure
are among the changes that result from living organisms. The
types of plants largely determine the kind and amount of organic matter that go into a soil under natural conditions. Some plants
add to the soil with falling leaves or fibrous roots while others
take their nitrogen from the air and add it to the soil as they
die. The bacteria and fungi that live on plant and animal residues, break down complex compounds into simpler forms as in the decay
of organic matter.
3. Parent Material. This is sometimes called a passive factor'in
soil formation. Rocks must be weathered to form parent materials.
These are further changed as horizons develop in a soil profile.
The composition and structure of rocks strongly influence the
rate of weathering and the products of that weathering. These,
in turn, are important to the kind of soil that may be formed.
4. Topography. Topography or the lay of the land affects run-off
and drainage. Run-off is generally greater on steep slopes than
on small or moderate ones. The amount of water that moves
into the soil depends partly upon topography. If the slopes are
steep, run-off will be greater and relatively little water is taken
into the soil. Run-off on steep slopes usually removes soil.
5. Time. Time is required for soil formation. The amount of
time depends on where the processes must start. The development of soil from freshly exposed and fairly pure limestone
takes a long time. Other types of stone dissolve much faster.
As a rule, more time is needed for the accumulation of soil parent
materials than for the differentiation of the horizons in the profile. Because of weathering during the past centuries, a regolith now exists over all of the continents. Soils have been formed on most land surfaces many times since molten lava first crystallized into rock many years ago.
None of the five factors of soil formation are uniform over the face of the earth. Variations are wide. There are many climates, many combinations of living organisms, many kinds of rocks, many topographies, and many different ages of land surfaces. As a result, there are hundreds of thousands of different local combinations of factors that affect soil formation.
C. SOIL CLASSIFICATION
Differences exist in the soil found in small geographic areas. Every farm consists of several different soils usually referred to as soil types. A single farm may have three to six types of soils within its boundaries. Each one occurs in a definite geographic region and in certain patterns. Regional soils differences are related to the distribution of climate and living organisms. In some places, these variations reflect differences in topography, age of land surfaces, or character of *parent rocks. There are also soil variations in such qualities as fertility, tilth, ability to hold available moisture, and susceptibility to erosion.
Throughout the world, six broad soil belts are outlined on a soil map of the earth. These are classified as:
1. Mountain, Soils. This belt consists of mountains and similar rough
landscapes in which many of the soils are stoney and/or shallow.
2. Tundra. The tundra region has a cold climate which restricts
'biological activities and horizon differentiation. The soils are frozen for a large part of each year. The deep regolith is per-nanently frozen in some parts of the tundra.
3. Podzols. Podzolic soils dominate a broad belt in the higher
latitudes of the northern hemisphere and some smaller areas in the southern half of the world. Podzolic soils are strongly
weathered and leached. Theyiare commonly acid, low in bases such as calcium, and low in organic matter. Levels of fertility
are moderate to low. Available moisture capacity is variable
depending on depth of soil and textures of horizons. As a group,
the soils are responsive to scientific management.
4. Latosols. These soils dominate equatorial belts of Africa and
South America. They are also dominant in parts of Asia and North America as well as Australia and the larger islands of
the Western Pacific Ocean. These soils are strongly weathered
and leached. In fact, they are the most strongly weathered
soils in the world. Despite being strongly weathered and deep, most of the soils lack distinct horizons. Red and yellow profile
colors are common to latosolic soils due to the large amounts
of ironoxides formed through intense weathering. Available plant nutrients are generally low when these soils are used
without benefit of modern science.
5. Chernozems. These soils have been formed under prairie or
grass vegetation in climates humid to semiarid and temperate
to tropical. They include the great soil groups known as'
prairie soils and'chestnut soils. In tropical and subtropical
regions these are known as black cotton soils, regurs or dark clay. Generally, these soils have dark "All horizons of great
thickne ss. They are also the most productive soils as they are
much higher in organic matter, have less alkalinity, and are
lower in bases than the desert soils. Available moisture holding
capacities of the soils are usually moderate to high. These are generally the most fertile soils in the world. Chernozem soils
of tropical and subtropical zones often have unfavorable physical
properties for tillage and plant growth. They are high in clay content and subject to shrinking and swelling. Their productivity under poor management is low, but they respond well to
good management practices.
6. Desert Soils. These soils have been formed under mixed shrub
and grass vegetation in arid climates, ranging from hot to cold.
These soils are prominent in the great deserts of Africa, Asia
and Australia, and in some of the smaller deserts of North and
South America. Desert soils are slightly weathered and leached.
The shortage of moisture which restricts weathering and leaching also limits plant growth leaving the soils low in organic
matter and nitrogen. The limited rainfall also causes the
shallow profiles normal in desert soils. Levels of nutrient elements other than nitrogen are usually moderate to high.
There are differences in the productivity depending upon the use
to which these soils are put.
D. SOIL - WATER RELATIONSHIPS
A soil, in order to function as a medium for plant growth, must
contain a certain amount of water. This moisture promotes the chemical and biological activities of the soil. The moisture acts as a solvent, carrier of nutrients, and functions as a *nutrient. The amount, kind and control of the soil moisture must be considered in any study of soil and plant relationships. The productivity of a soil is often a direct function of its water holding capacity. 0
Precipitation, which falls in the form of rain or snow, must be absorbed and retained by the soil to benefit plants. Soil water behaves differently according to the tightness with which it is held by the soil. When the water film surrounding a soil particle is thick enough, the attraction of the soil for the water in the outer edges of the film will be so slight that the outer water will be subject to the influence of gravity.
Four forms of soil water are usually recognized. These are:
1. Gravitational Water. Gravitational water percolates downward
through the subsoil by the force of gravity and drains away.
2. Capillary Water. Capillary water is held by the soil against
the pull of gravity. It can move to a certain extent in any
direction in response to capillary tension. This form of water
can be removed by air drying and, to a certain extent, by
3. Hygroscopic Water. Hygroscopic water is that water which is
retained by an air dry soiL It can be removed only by oven
drying for several hours at a temperature of 1050 centigrade.
4. Combined Water. This remains after hygroscopic water has
been removed. It is held in chemical combination and is driven
off only when subjected to high temperatures.
Since the free or gravitational water rapidly drains away from the root zone in well drained soils, it is not normally available for plant use. Of the capillary water that remains, the amount available to the plant is that which is in excess of the wilting point. The wilting point is the percentage of water remaining in the soil at the time permanent wilting occurs. At the wilting point, there is still some capillary water present in the soil but it is held with such tension that it cannot be removed by the plant.
The movement of water by capillary action is affected by anything which affects the size and continuity of the pores. Water will rise faster above the water table in a coarse textured soil in the early stages but it will eventually rise to a greater height in a fine textured soil. Movement Pf water by capillary action is faster through a wet soil than through a diy soil.
The amount of water that a given soil can hold is a function of the number and size of the individual pores rather than the total amount of pore space. Thus, a coarse or sandy soil will not hold as much water as a fine textured clay soil.
When all of the pore space, of a soil is filled with water, it is said to be saturated. When a soil contains the maximum amount of the water that it can hold against the force of gravity, it is said to be at field capacity.
A good rule of thumb for medium textured soils is that the field capacity'is approximately one-half the maximum retentive capacity and the permanent wilting point is approximately one-half of the field capacity.
Soil moisture is very important to plant growth because nutrients that a plant takes into its system for growth, go into solution with water before the plant can utilize these nutrients as plant food.
E. PHYSICAL PROPERTIES
Physical properties of the soil generally mean the size, shape, and arrangements of its particles; the volume and form of its pores; the effective depth of soil from which plants may draw nutrients; and the mineral composition. The flow and storage of water, the movement of air, and the ability of the soil to supply nutrients to plants are determined by its physical properties. These properties differ greatly between the large and small particles. The large size particles are stones, gravels, and sand, and the smaller size particles are called silt and clay. The individual particles of gravel, sand, silt, and clay occupy about one-half of the total volume in a soil. The. voids between the particles are called pore space and is occupied by water and soil air. The following are the
00 0 .0
Texture triangle showing the percentages of sand, silt and clay in the textural classes. The intersection of the dotted lines shows that a soil with 55 percent clay, 32 percent silt and 13 percent sand has a clay texture.
STICKY WHEN WET, CLODS WHEN DRY
MEDIUM RIBBONS WHEN MOIST, CLODS WHEN DRY
NO RIBBONS WHEN MOIST, SOFT CLODS WHEN DRY
Modified textural triangle for determining soil texture
by the feel method.
physical properties of soil which are considered in soil management:
(1) texture, (2) color, (3) depth, (4) structure, (5) permeability,
(6) moisture -holding capacity, (7) surface drainage, (8) slope.
1. Soil Texture. Soil texture relates to the relative proportions
of sand, silt, and clay that are present in the soil. A large
amount of sand in a soil will make it coarse and gritty. Such
soil may be called sand or sandy loam. It is generally referred
to as light soil because it is easier to till. If silt is present in large quantities, the soil feels like flour, is medium in texture,
and may be called silt loam or loam. Conversely, a large
amount of clay in the soil makes it sticky when wet and hard
when dry. Such soil is termed a heavy soil and may be classified as clay or clay loam. Generally, the medium textured soils are considered the best in respect to moisture holding
capacity and ease of tillage. Sandy soils are usually well drained,
well aerated, and of low water holding capacity. In nature, sand, silt, and clay are almost always mixed together in a
great variety of combinations which give the soil its characteristic texture. Physically, the inorganic portion of the soil, called soil separates, is divided into fractions called sand
(2.00 - 0.05 mm), silt (0.05 - 0.002 mm), and clay (less than
0. 002 mm).
DIAMETER AND CHARACTERISTICS OF SOIL
Soil Diameter of
Separate particles General Characteristics
Sand 2-.05 mm Individual particles feel gritty when
the soil is rubbed between the fingers. Not plastic or sticky when moist.
Silt .05 - . 002 mm Feels smooth and powdery when
rubbed between the fingers. Not plastic or sticky when moist.
Clay less than Feels smooth, sticky and plastic
002 mm when moist. Forms very hard clods
when dry. Particles may remain suspended in water for a very long period of time.
Z. Color. Soil color is one of the most noticeable soil characteristics and is widely used to distinguish one soil from another.
Yet soil color has relatively little meaning in itself. The color
of the top soil is sometimes an indication of soil drainage. Well
drained soils generally have a uniform brown color when moist
but, in some cases, there may be various shades of red or yellow
resulting from the presence of iron or aluminum oxides. A pale
or gray color denotes poor drainage. A black surface usually indicates that the land is either rich in organic matter or has remained wet.for long periods. This is not a sure formula as
parent material also enters into the color of soil. ,
3. Soil Depth. Soil depth is important to plant growth because- it is
related to the storage of water, plant nutrients and root extension.
The depth of a soil can be observed in roadcuts, stream banks, or
by digging pits. The section or face of the exposure made by a
cut is called a soil profile and may exhibit a succession of separate
layers. Although these layers may or may not be separated by sharp lines of demarcation, the upper portion usually contains
more humus and is darker in color. This is called the "A"
horizon. Usually a finer textured soil body containing little or
no organic matter lies below. This may be several feet in
thickness, and is called the "B" horizon. As the weathered s oil
material of the "B" horizon merges with the original parent
material the area known as the "C" horizon is encountered. The
effective depth of the soil is determined by the depth of soil
readily penetrated by plant roots. In a deep soil, plants withstand drought better because the roots are spread. through a
larger volume of soil. Also, minerals stored in the subsoil are
used by plants if roots can reach them. Soils are sometimes
classified as very deep soils - over 48 inches in depth; deep soils
36 to 48 inches; moderately deep 24 to 36 inches; shallow
1 Z to 14 inche s; and ve r y shallow le s s than I Z inche s.
4. Structure. Structure is perhaps one of the most important
physical characteristics of soil, yet it is probably the least understood. Sand, silt, and clay seldom occur as separate units in the soil, but combine into small aggregates. These
aggregates are structured into prisms, columns, blocks, plates,
or granulars. The most common aggregates found-in soils are
clods, which are more specifically called blocks. Granular
structure is most desirable for a seedbed and is the structure
which many farmers attempt to develop in the soil by cultivation.
The type of structure has a great effect on the permeability of
the soil. Top soil structure may be improved by organic matter
and cultivation. Soil structure has a direct relationship to soil
productivity, soil permeability, and root growth.
5. Permeability. Permeability refers to the movement of water
and air through a soil. The rate of water intake, water capacity, depth of root penetration, and degree of internal drainage are all related to permeability. Soils which have sandy or gravelly subsoils have rapid permeability. Subsoils which contain ample amounts of sand and silt have moderate permeability. If subsoils have large amounts of -clay and silt they are slowly
6. Moisture -holding Capacity. This refers to the amount of water
that can be stored by a soil for use by plants. In general, the
coarser the soil, the lower is the moisture -holding capacity.
Conversely, the finer the soil the higher the moisture -holding
capacity. Sandy soils are coarse and have a much lower water
holding capacity than do clay soils.
7. Surface Drainage. This refers to the relative rate for drainage
(removal) of excess water from a soil surface. If water is
removed so slowly that the soil remains wet for a long period of
time, then the surface drainage is poor. Sometimes surface water may be removed in excessive amounts causing drought
8. Slope. Slope is measured in degrees but is expressed as a
percentage number for convenience. This percentage number
is the difference in elevation from one end of a field to another.
For example, a difference in elevation of five feet per 100 feet
of field length would mean a five percent slope to the field.
Fields can be classified as:
a. Nearly level - less than one foot rise or fall in each 100 feet,
b. Very gent ly sloping - one to three feet rise or fall in each
C. Gently sloping - three to five feet rise or fall in each 100 feet,
d. Moderately sloping - five to ten feet rise or fall in each
e. Strongly sloping - ten to fifteen feet rise or fall in each 100
f. Moderately steep to steep - fifteen to twenty-five feet rise
or fall in each 100 feet.
- 1. 1. -
F. SOIL REACTION
Soils are neutral, acid, or alkaline in reaction. Their degree of acidity or alkalinity is expressed as pH. The term pH is a symb ol and is the chemist's means of expressing active acidity or alkalinity.,
Acid soils are found chiefly in areas of heavy rainfall. Under any particular rainfall condition, acid soils are more readily formed from acid igneous rocks such as granites and secondary rocks such as sandstone than from basic igneous rocks such as basalts.
Soil acidity is due partly to the process of plant nutrition, to leaching, and, in part, to the weathering of soils. Muck or peat soils develop acidity largely from organic acids which are formed in the decay of large amounts of organic matter. In the case of mineral soils, soil acidity might be defined simply as a condition of low base saturation.
As a plant functions, and carbon dioxide isgiven off by the roots,
carbonic and other mild organic acids are formed in the soil. These acids yield hydrogen which competes on the exchange complex, (primarily the clay particles and soil organic matter) for the bases which, in turn, are taken up by the roots of the plant or leached out of the soil.
The hydrogen ions which cause acidity or characterize acidity compete in the soil with bases such as calcium and magnesium of limestone, potassium and sodium of commonly used fertilizers, and such other bases as manganese, copper, zinc, and iron in lesser amounts.
Soil acidity.and soil alkalinity present extremes in the equilibrium of these elements under soil conditions. In high acidity, the effect of the hydrogen ion (H+) predominates. In high alkalinity, it is the effect of the sodium ion (Na+) producing hydroxyl ions (OH-). Both conditions result from a deficiency of calcium ions (Ca++) on the exchange complex. An increase in the amount of calcium on the exchange complex will help overcome such deficiency.
G. SOIL FERTILITY
Soil fertility refers to the nutrient supplying properties of the soil. Plants, like any other living thing, need food to live and grow. If they are well fed they will generally grow vigorously, be somewhat resistant to insects and diseases, and will give a good yield. If they are poorly fed they will grow slowly, becomeweak or generally susceptible to insects, and diseases, and usually produce low yields.
There are sixteen elements, listed below, which are e ' essential for normal plant growth and development. Carbon, hydrogen and oxygen are usually obtained by plants from water and air. The remaining elements are obtained from the soil solution and are referred to as primary plant food elements, secondary plant food elements, or micronutrients (elements plants require in microscopic amounts).
1, Carbon. This comes from carbon dioxide in the air. It functions
as an element in cell walls. It is a component of plant sugars, a
part of the structure of color, and even an element in the fragrance
of plant blossoms.
2. Hydrogen. One of the two elements composing water. This
element is essential to the plant with carbon and oxygen. It is used in the plant cell in the manufacture of simple sugars and
3. Oxygen. One atom of this element, combined with two atoms of
hydrogen, forms water. Oxygen also combines with other elements
- to form oxides and complex organic compounds.
Primary plant food elements:
4. Nitrogen. Nitrogen is the essential element for building plant
materials in the cell. It promotes rapid vegetative growth and
gives plants a healthy green color. It improves the quality of
leaf crops and tends to increase the protein content of all crops.
Nitrogen deficiency may be observed by pale, yellow coloring, stunted growth, and the "firing" of tips and margins of leaves.
Nitrogen deficiency also shows up in low protein content.
5. Phosphorous. Phosphorus is essential to all plant growth and is
an active ingredient of protoplasm. It stimulates early growth
and root formations, hastens maturity, promotes seed production,
gives stability to the stem, and contributes to the general hardiness of plants. Phosphate deficiency is characterized by small
growth especially in the root development, a spindly stock,
delayed maturity, and a purplish discoloration on the foliage of
some plants. Poor fruit and seed development are general
6. Potassium. Not too much is known about the function of potassium
intheplants. More is known about what happens when potassium
is deficient. It is generally agreed that potassium enhances a
plant's resistance to disease, tolerance of cold, and other adverse
conditions. Potassium deficiency usually results in a slow growing
plant. The margins of the leaves develop a scorched effect, starting first with the older leaves. The plants lodge easily,
the fruit or seed is somewhat shriveled, and the plants seem to
have low resistance to rust and other diseases.
Secondary plant food elements:
7. Calcium. Calcium is believed to help in the translocation of
carbohydrates in the plant. It is considered essential to healthy
cell walls and aids in the development of root structure. Calcium
is the active element in liming materials used to correct soil
acidity. It also occurs in gypsum which is used in the treatment
of saline and alkali soils. Calcium deficiency is generally
characterized by the terminal bud or growing point of the plant
dying under severe deficiency and the margins of affected leaves have a scarlet appearance. The foliage not so affected is usually
abnormally dark green. The plant has a tendency to shed its
blossoms and buds prematurely and sometimes the stem
structure is weakened.
8. Magnesium. Magnesium is an essential ingredient of chlorophyll
and aids in the translocation of starch within the plant. It is also essential for the formation of oils and fats and aids in the translocation and absorption of phosphorous in plants. Magnesium
deficiency is generally indicated by leaves losing their color at
the tips and between the veins, starting with the lower leaves and proceeding upward, depending upon the degree of deficiency. The leaves are abnormally thin. Leaves of plants are brittle and have
a tendency to curve upward.
9. Sulphur. Sulphur is associated with plant protein. It also aids in
the synthesis of oils. Sulphur deficiency is characterized by the
lower leaves turning yellowish-green. Stems are small in
diameter and hard and woody. Although root growth is sometimes
well developed and extensive, the roots are small in diameter.
10. Boron. Boron is associated with calcium utilization within the
plant. Whenever the proportion of calcium to boron becomes unbalanced because of a deficiency of boron, the terminal part
of the plant fails to develop properly. The amount of boron
required by plants is extremely small; however, even a slight
increase over the required amounts will sometimes bring severe
toxicity. Symptoms of boron deficiency usually show marked changes in the tip of the growing point of the plant, sometimes
being tinged with reddish brown areas. The terminal bud
becomes light green in color. In root crops, boron deficiency
,results in a brown heart characterized by dark spots on the
thickest part of the root, or splitting at the center.
11. Copper. Copper is an activator or catalyst of other reactions
within the plant. It seems to promote the formation of Vitamin A
and appears to have a regulating function if soil nitrogen is too
high. An excess of copper is very toxic. Copper deficiency
symptoms result in foliage with a chlorotic condition which gives
a bleached appearance. Citrus fruits show a die-back of new
growth. In citrus fruits, also, the trees are marked with a
12. Iron. Iron is essential for the formation of chlorophyll. Iron
apparently enters into the oxidation processes which release energy from sugars and starches. Iron deficiency symptoms show chlorosis of leaves - the youngest leaves being affected first, then the points and margins of leaves are affected while
the veins remain green. The affected leaf is sometimes curved
in an upward direction.
13. Manganese. Manganese is closely associated with copper and
zinc and also acts as a catalyst in plant growth processes.
Manganese deficiency symptoms result in a chlorosis between the veins of the young leaves. Even the smallest branches of
the veins remain green while the tissue between the veins is
light-green, yellowish or almost white. Loss of color is often followed by development of spots of dead tissue which may even
drop out giving the leaf a ragged appearance. Sometimes the
entire plant is considerably dwarfed.
14. Molybdenum. Molybdenum is associated with nitrogen utilization.
Very small amounts are needed. Plants containing an excess of
this element are sometimes toxic to livestock. Deficiency
symptoms show plants stunted and yellow in color closely
resembling nitrogen deficiency plants.
15. Zinc. Zinc is apparently linked with iron and manganese in the
formation of chlorophyll. Deficiency symptoms usually show
terminal leaves abnormally small - a condition known as "little
leaf" in fruit trees. Fruit bud formation is severely reduced.
Some plants have mottled leaves and dead areas.
16. Chlorine. Chlorine is the latest element established as essential
for plant growth. In plant life, it is believed to stimulate the
activity of some enzymes, to influence carbohydrate metabolism or the production of chlorophyll, and the water-holding capacity of plant tissue. Generally, there is no deficiency of chlorine in the soils except in the humid regions. Normal rainfalls supply
sufficient chlorine to maintain a normal supply in the soils.
We speak of plant food elements removed from the soil by crops. The three elements - nitrogen, phosphorous, and potassium, which we have termed primary elements, are also called the fertilizer elements and are indicated by the symbols N, P, and K. Thu's a fertilizer is termed a complete fertilizer when it has the three elements (N, P, and K) in its formula. These three elements are all needed by plants in substantial quantities. Each must be furnished to the plant from supplies in the soil, or added to the- soil by manures or chemical fertilizers. The so-called micronutrients are needed by plants in comparatively small amounts and are usually present in soils in quantities sufficient to meet the needs of the plant. It is generally the quantities of N, P, and K in the soil which determine its fertility.
Various crops differ in their nutrient needs. One crop may require more nitrogen while another may require more phosphate. Generally speaking, the higher the yield of a crop, the greater the demand for all the necessary elements.
H. APPLICATION OF FERTILIZERS
As a general rule, the best time to apply fertilizer to any crop is before the main growth has started. This, of. course, will depend on a number of factors such as the type of crop, soil, weather, and moisture conditions. It is often the practice to apply a phosphate fertilizer to fall sown grains at seeding time and top-dress with a nitrogenous fertilizer ,early the following spring. Corn is often fertilized at seeding time and given an additional amount of nitrogen fertilizer when the crop is well established. Other intertilled crops are given similar side dressings of fertilizers as the crop or excessive leaching demands.
Fertilizers are usually applied in one of several ways. They are either broadcast over the entire soil surface, placed in the hill or row close to the seed or root, or incorporated into the soil during plowing or cultivation.
Top-dressing, or broadcast fertilization, is widely used in orchards, pastures, and for general grain and legume crops. Penetration of the nutrients into the root zone is accomplished by rainfall and irrigation water or by injecting an anhydrous or aqua solution into the soil. Another method of top-dressing is the application of liquid or soluble dry fertilizer materials into the irrigation water.
Direct contact of seed with nitrogen and potassium fertilizer in the soil may have a detrimental effect on the germination of the seed. Grain drills with fertilizer distributing attachments are preferred to mixing the fertilizer with the seed even though small grains can tolerate some contact. Placement machinery has been developed which will place the fertilizer an inch or two below the seed.
Placing the fertilizer under the soil surface in a strip or band to the side and below the seed has proven efficient. Localized applications give more efficient use of smaller amounts of fertilizer and does not readily assist weed growth. Because fertilizer has a tendency to move up and down with only a small amount of lateral movement, placement of fertilizer directly below the seed may be detrimental to seed germination as well as taproot development.
Side dressing is the banding of fertilizers after the plant has emerged. Materials are usually banded along the side of the bed or hill below the water line along the irrigation furrow. Good control of this placement puts the plant food within easy reach of the feeding roots during the growth period when the need is great.
When applying fertilizer in conjunction with irrigation water,
accuracy in measurement of the water as well as the fertilizer material is important for efficiency.
I. SOIL ORGANISMS
Raw organic matter in the soil is not directly useful to the plants. It must first be broken down into humus. and then into simpler organic products before it can be utilized. Decomposition of organic matter primarily forms part of the feeding and growth processes of billions of different microorganisms. Sugar, starches, and proteins are broken aown first; then cellulose and fatty substances; and lastly lignin or woody substances.
Not all soil organisms are beneficial. There are certain bacteria which release nitrogen to the air where it is lost for plant use. Some others cause plant diseases. Soil micro-organisms have been classified as:
Microflora: Bacteria, Actinomycetes, Fungi and Algae
Microfauna: Protozoa and Nematodes
Besides these, the soil also harbors a large number of worms and insects of different kinds and sizes.
The soil organisms vary in numbers from a few per acre to many
millions per gram of soil. The density of organic population is determined by food supply, moisture, temperature, physical condition and chemical reaction. In more or less neutral soils, bacteria dominates the microscopic life. If the soil is acid and rich in organic matter, fungi predominate. Algae abound near the surface in constantly moist and shady localities.
One of the most important types of bacteria is collectively known as nitrifying bacteria. These bacteria attack the complex organic material, and change the nitrogen compounds to ammonia, the ammonia to nitrites, and the nitrites into nitrates. Though found in most cultivated soils, the nitrifying bacteria are generally confined to the top ten to twelve inches. They work best at temperatures between Z5 and 380 C, and under conditions of thorough tillage, good aeration, and soil moisture content of approximately 60% of the total moisture holding capacity.
Two other groups of bacteria take up free nitrogen from the air and convert it into nitrogenous compounds for the use of plants. One group functions symbiotically with leguminous plants while the other fixes free nitrogen independently of the legumes. The amount of nitrogen added to the soil by these bacteria varies from 50 to 150 pounds per acre.
Most of the soils are inhabited by worms, insects, and other animals of different sizes. It has been estimated that the earthworms in an acre of soil will pass fifteen tons of soil through their bodies leaving castes weighing 16, 000 pounds per acre. Earthworms help form favorable soil structure and improve the nutrient status of soils.
Insects and some other larger animals assist aeration and water
percolation. They make channel and burrows in the soil for protection or in quest of food.
J. SOIL CONSERVATION
Soil and its related productivity is our greatest natural resource. Once lost, it can never be replaced. Yet, year after year, tons of rich topsoil are lost through carelessness and poor farming methods. This loss is brought about by either wind or water.
Water erosion is generally classified into three types: gully, rill,
and sheet erosion. In gully erosion, soil losses are generally of such a nature that channels large enough to interfere with mechanical cultivation are formed. Rills are thought of as small gullies not large enough to interfere with mechanical operations. Sheet erosion is not easily observed, but often cailses more damage than gully or rill erosion. It removes a thin covering more or less uniformly during every rain producing a runoff.
Each year erosion costs Anerican farmers several millions of
dollars through reduced productivity of the land. Floods devastate large areas of city and farm land. Accidents in which farm tractors roll over into gullies annually cause several deaths.
Soil erosion by water action is influenced greatly by precipitation, percent slope, length of slope, type of soil, and the nature of the ground cover.
Rainfall is the most important, factor influencing soil erosion.
Intensity, duration and frequency influence the rate and volume of runoff. As intensity of rain increases and the soil becomes saturated, soil loss results from the runoff. Rainfall of long duration and greater frequency increases both the total runoff and soil loss.
The speed and extent of runoff increases as the slope of the land
increases. Therefore, soil loss increases rapidly as the slope of the field becomes steeper.
The type of soil, i. e. , its structure, texture, organic matter content, infiltration capacity and permeability greatly affect soil loss and runoff. Soil left in a loose and pulverized condition is particularly liable to erosion through sheet wash and gullying.
When rain falls on a surface covered by a thick mantle of plants, its velocity and erosive powers are reduced. Most of the water either quickly percolates into the soil or moves over the surface with non-erosive velocity. Areas not so protected are unable to absorb the water as effectively. The dashing rain shatters the soil surface. The fine soil particles go into solution or suspension and the thick mixture of water and soil quickly fills and closes the pores in the soil. Infiltration is drastically reduced while runoff and soil loss is increased.
Effective methods have been developed to minimize soil erosion and
are being employed on thousands of farms. The basic factor in the application of soil conserving practices is the proper utilization of the land according to its capabilities.
This is largely a matter of crop adaptation and management. Management practices which contribute to the conservation and productivity of agricultural lands form what is known as conservation farming.
One of the most successful methods of controlling runoffs on sloping land is to carry out all cultivation operations and to sow all crops along the contour. Farming on the contour reduces runoff, saves more moisture for crop production, reduces soil losses and increases crop yields.
Incorporation of organic material into the top few inches of the soil has aided in controlling both wind and water erosion.
Strip cropping is the growing of a sod crop in strips of suitable width across slopes, alternating with cultivated crops. This is essentially a form of crop rotation and is important in controlling runoff erosion.
Using grass as stabilizing agents is recommended in many areas.
Permanent waterways stabilized with sod aid in removing excess water from the land. Using a grass crop as a part of the rotation assists in holding the soil in place. Areas of severe erosion should be permanently returned to grass.
Mechanical soil conservation measures are adopted to supplement the cultural methods. The design of mechanical structures to control erosion are based on three general principals:
1. Allowing more runoff water to be absorbed and held by the soil.
Z. Dividing a long slope into several short ones to maintain a minimum
velocity for the runoff water.
3. Protection against damage due to runoff such as basin listing, contour terracing, ponds, etc.
Where erosion is relatively mild, the most effective control is obtained through a combination of crop rotation and striving for maximum yields. Research has shown that if the organic matter content of the soil is high, the rate of erosion is reduced. A crop rotation including perennial forage crops results in better maintenance of organic matter than continuous cropping to row crops. Similarly, when crops are managed in such a way that maximum yieldss are obtained, the soil is protected in two ways. The increased top growth protects the soil from the beating force of rain or wind and the higher yields result in more crop residues, especially roots, being left in the soil as organic matter.
CHAPTER II - PLANTS
That branch of science which deals with the study of plants is called botany. Plants occupy a very prominent position in our lives. It is the green plants that keep the air we breath supplied with oxygen. Plants supply us with all our primary biological needs. However, they also cause many of the most serious diseases of man. At the same time, they provide many of the medicines used to cure disease. It is by working directly with plants or with plant products that a majority of the world's workers earn a living.
B. CLASSIFICATION OF PLANTS
Plants may be classified in different ways. Many different systems have been used, but the one most generally accepted is based upon the similarity or relationship of plant parts. According to this system, the entire plant kingdom is subdivided into the Thallophyta, Bryophyta, Pteridophyta, and Spermatophyta divisions.
The lowest division, Thallophyta, is characterized by plants that have no roots, stems, or leaves. Many of these plants consist of but a single cell and are relatively simple in structure. Many, like algae, live entirely in water. Others like toadstools and mushrooms grow on dry land or on dead and decaying matter. All bacteria belong to this group, living in the soil on dead and decaying matter or in other living organisms where they sometimes cause disease.
The Bryophyta division is made up of the so-called "moss plants". These plants also lack roots, stems and leaves as we generally think of them. They differ from the Thallophytes primarily in their reproductive system. To this division belong all the common mosses and their relative, the liverworts, both of which are found living in moist places or in water.
The ferns exemplify the third group called the Pteridophytes. These plants differ from the two lower divisions in that they have true roots, stems, and leaves. They also have a well defined conducting system. They differ from the higher plant division in that they do not produce flowers, fruits, and seeds. This group is made up of the ferns and their close relatives, the club mosses, horsetails, and scouring rushes.
The highest division of the plant kingdom, called the Spermatophytes, contains all crop plants as well as all the common trees, shrubs and flowering plants. These plants all have roots, stems, leaves and a highly developed conducting system. The most important feature is that they produce seed.
The Spermatophyta division is divided into two subdivisions; the
gymnosperms and the angiosperms. The gymnosperms are characterized by producing their seeds exposed. The term gymnosperm means naked seed. This group is represented in temperate regions by the pine, spruce, cedar and other evergreens. The angiosperms produce their seed enclosed in a fruit. The members of this group are very numerous and embrace all of the well known flowering plants.
The angiosperms are further subdivided into two classes; the
monocotyledons and the *dicotyledons. The essential differences between these two groups are: (1) The embryo of the monocot contains but a single cotyledon or first leaf while the dicots contain two. (2) The organs of the flowers in the monocots are usually in threes or multiples of three, while in the dicots, they are mainly in fours or fives or multiples of these numbers. The monocots are represented by the grass-like plants, such as corn, wheat, oats and other grasses, and other plants such as the lily, bamboo, and banana. The dicotyledons include the broad-leafed forest plants and many ornamental and crop plants such as beans, peas, clover and buckwheat.
This classification goes several steps further. The classes are divided into Orders. The orders are broken down into families, the families into genera, and the genera into species. Oftentimes, the species are further subdivided into varieties.
.The following example illustrates the complete classification of sweet corn.
Division Sp ermatophyta
Variety Golden Bantam
For more practical use, plants are often classified according to their botanical relationships, their use, the cultural treatments imposed, the seasons in which they grow or according to their life-cycle.
We need to become more specialized in the identification of the
more common plant families. Consequently, Figures 3 through 42 provide an illustration and short description of the members of the herbaceous flowering plant families as an aid to their differentiation and identification.
Annual or perennial grass-like herbs with triangular solid stems and 3-ranked leaves; the leaf sheath closed; flowers in spikelets with 2-ranked or spiral scales, with or without basal bristles, or sometimes in a sac-like structure.
Figure 3 - CYPERUS
GRASS FAMILY'l (gramineae)
fAnnual or perennial herbs with
round, hollow stems and 2-ranked leaves, and a leaf sheath split.
Figure 4 - CRAB-GRASS
RUSH FAMILY - ,
Mostly perennial, grass-like, usually tufted herbs; papery and glume-like.
Figure 5 - RUSH
/T>\ a SPIDERWORT FAMILY
(commelinaceae) Mostly perennial more or less lilylike plants with a short inflated
leaf sheath; sepals 3 green, petals 3, usually blue, wither very rapidly.
Figure 6 - SPIDERWORT
Mostly tall herbs with opposite stipulate leaves, sepals 4; corolla none; stamen 4; fruit an achene. Flowers are greenish.
Figure 7 - TALL NETTLE
Perennial herbs or a few woody vines, mostly with bulbs, corms, or rootstocks; inflorescence various; sepals 3, usually like the petals; petals 3; and perianth parts separate or united.
(A) WESTERN LILY (B) STAR- OF- BETHLEHEM (C) WILD GARLIC
(D) SMOOTH SOLOMON'S SEAL (E) ROUNDLEAF GREENBRIER
BUCKWHEAT FAMILY (polygonaceae) Herbs with alternate leaves and sheathing stipules; corolla none; sepals 4-6, greenish or pinkish.
Figure 9 - DOCK
Annual herbs with alternate, mostly mealy coated leaves, without stipules; flowers small, greenish, in tight groups; sepals usually 5.
Figure 10 - LAMB'S QUARTERS
AMARANTH FAMILY (amaranthaceae) \ Coarse annual herbs with alternate
.i i.- leaves without stipules; flowers
bracted; sepals usually 5; stamen usually 5; and style Z or 3.
Figure 11 - ROUGH PIGWEED
Annual or perennial fleshy-leaved herbs without stipules; our common weed prostrate; flowers small, terminal; sepals 2; petals 5; and stamen 8 or more.
Figure 12 - COMMON PURSLANE
CARPET-WEED FAMILY (aizoaceae)
Annual prostrate herbs branched at base; leaves narrow, in whorls; flowers small whitish; sepals 5; corolla none; stamen 3 or 5; style 3.
Figure 13 - CARPET-WEED
Medium tall herbs with opposite 'leaves; flowers above a 5-lobed involucre; corolla none; caylx tubular, petal-like, 5-lobed; stamen 3-5; style 1.
Figure 14 - UMBRELLA-WORT
PINK FAMILY (caryophyllaceae) Annual or perennial herbs with opposite leaves and short or no petioles; flowers white, pink or red; petals 5, mostly notched at apex; sepals mostly 5, often A Bunited; stamen usually 10; style
A B 2-5; often toothed at top when open.
Figure 15 - (A) CATCHFLY (B) CHICKWEED
Herbs with 3-5 parted leaves;sepals 5; petals 5; stamen usually 10; style united to form a beak; ovary 5-lobed and 5-celled; fruit a 5-celled capsule; each cell I- or 2-seeded.
*opposite or alternate
CROWFOOT FAMILY 0 (ranunculaceae)
Annual or perennial herbs with alternate mostly compound or lobed leaves and no stipules; flowers mostly showy, regular, or irregular and spurred; sepals 3-15, often petal-like; petals same number as sepals or none; stamen many; carpels few to many, great variation, pistils not united; flower parts on receptacle.
Figure 17 - (A) LARKSPUR (B) ANEMONE
Mostly annual or biennial herbs with alternate, entire or variously lobed leaves; flowers mostly white or yellow; sepals 4; petals 4; stamen 6 with inner 4 B
Figure 18 - (A) MUSTARD (B) FIELD PEPPERGRASS
A PEA FAMILY
Herbs, herbaceous vines, shrubs or trees with alternate, mostly compound leaves with stipules; flowers irregular and mostly beanlike; cayix 4-5 toothed, petals 5 B-O usually more or less united; stamen
B mostly 10, united in 1 or 2 sets,
C jointed between the seeds in 1 tribe.
Figure 19 - (A) BLACK MEDIC (B) VETCH (C) TICK CLOVER
Mostly perennial herbs, shrubsAB or trees, most with compound leaves and conspicuous stipules; flowers mostly showy, white, yellow or pink; sepals 5; petals 5; stamen numerous; carpels 1 -many.
Figure 20 - (A) ROUGH CINQUEFOIL (B) AGRIMONY
/ WOOD SORREL FAMILY (oxalidac eae)
Annual or perennial low herbs with sour sap and clover-like leaves; sepals 5; petals 5; yellow or pink; stamen 10-15; style 5 or (united; 2-several seeds in each cell.
Figure 21 - YELLOW WOOD SORREL
Herbs with alternate, mostly compound leaves; flowers inW umbels, mostly white or yellow, small, caylx 5-toothed, adnate *
to ovary; petals 5; stamen 5.
Figure 22 - WATER HEMLOCK
MALLOW FAMILY (malvac eae)
Herbs or shrubs with alternate leaves; sepals 5, somewhat united; petals 5, stamen many, united in a tube around style; style united except at apex.
Figure 23 - ROUNDLEAF MALLOW
Herbs with alternate, opposite or whorled leaves; flowers mostly small; sepals 5-6 or none; petals 5-6 or none; involucre calyx-like in some; stamen few-numerous; style mostly 3; plants with milky juice.
Figure 24 - SPURGE
EVENING PRIMROSE FAMILY(onagraceae)
Annual or perennial herbs with
opposite or alternate leaves;
calyx tubular, mostly 4-lobed;
petals usually 4; style united except at apex; fruit a manyseeded capsule; stamen 4 or 8.
Figure 25 - COMMON EVENING PRIMROSE
Herbs, mostly rough hairy, flowers rather small, white, yellow or purple; calyx 5-lobed or parted; corolla tubular, 5-lobed at apex; stamen 5 on the corolla tube; style simple or 2-divided; nutlets often bur-like.
Figure 26 - (A) CORN CROMWELL (B) HOUND'S TONGUE
MORNING-GLORY FAMILY .(convolvulaceae) Mostly twining herbs with alternate leaves; flowers usually large; calyx 5-parted; corolla tubular, 5-lobed; stamen 5, low on the corolla tube; style entire to the stigma or 2-divided.
Figure 27 - HEDGE BINDWEED
Perennial herbs or vines, flowers mostly small, whitish or pinkish; calyx 5-parted; corolla tubular, 5-lobed or parted at apex; stamen 5, short, on the corolla; style 6.
simple or Z-divided; plants mostly with milky juice.
Figure Z8 - INDIAN HEMP
PHLOX FAMILY (polemoniaceae) Herbs with mostly opposite leaves; flowers mostly conspicuous; blue, white or pink; calyx 5-parted; corolla tubular, 5-parted at the apex; stamen 5 on the corolla tube; style long, 3 divided at apex; mostly many seeded.
Figure Z9 - PHLOX
Herbs, mostly conspicuously with alternate or basal, lobed or divided leaves; flowers conspicuous, white, blue or purple; calyx 5parted; corolla mostly short tubular, 5-parted at apex; stamen
5 on the corolla tube, often conspicuously exceeding the corolla; style Z or 2-divided.
Figure 30 - WATERLEAF
MILKWEED FAMILY (asclepiadaceae) Perennial herbs or vines with alternate, opposite or whorled leaves; flowers mostly in umbels, A A small; calyx short, 5-parted;
tA corolla 5-parted, mostly reflexed;
A stamen 5, united around the stigma;
style 2, joined to form a disk-like stigma; plants with milky juice.
Figure 31 - MILKWEED
Twining, yellow or white parasites on green plants; flowers small; calyx 5-lobed or parted; corolla 5-lobed, stamen 5, on the corolla tube; style 2.
MADDER FAMILY (rubiaceae)
Mostly low herbs with opposite or whorled leaves; calyx tubular, 4-lobed; corolla tubular, 4-lobed; stamen 4 on corolla tube.
Figure 33 - (A) BUTTONWEED (B) CLEAVERS
Herbs, mostly aromatic punctuate, with opposite leaves; flowers mostly small, irregular, /
mostly in axillary or terminal groups; calyx 5-lobed or toothed; corolla 2-lipped, the lower lip AB
3-lobed; the upper 1- or 2-lobed. tubular; stamen 4, rarely 2, usually 2 long and 2 short, on the corolla tube; style 1; plants with square stems.
Figure 34 - (A) WILD BERGAMOT (B) MOTHERWORT
HONEYSUCKLE FAMILY (caprifoliaceae)
Mostly shrubs and vines with opposite leaves; calyx tubular, 3-5 lobed; corolla tubular, 5-lobed, sometimes 2-lipped; stamen 5 on corolla tube; mostly berries or B drupes.
Figure 35 - (A) JAPANESE HONEYSUCKLE (B) ELDER BERRY
Low herbs with basal leaves; calyx 4-parted; corolla tubular, 4-lobed, papery; stamen mostly 4, on corolla tube; style 1; flowers with bracts.
Figure 36 - PLANTAIN
// Tall herbs with opposite leaves;
calyx tubular; corolla tubular, 4-lobed; stamen 2-4 on corolla tube; flowers with bracts.
Figure 37 - COMMON TEASEL
Herbs with opposite leaves, ours mostly hairy; flowers in spikes, bracted, mostly white or purplish blue, small; calyx 4-5 lobed or cleft; corolla tubular, 4-5 lobed at apex, regular or somewhat 2-lipped; stamen 4, 2 long and
2 short, on the corolla tube; 4 Xn
Figure 38 - BLUE VERVAIN
FIGWORT FAMILY(scrophulariaceae) \ I Herbs with alternate or opposite
leaves; flowers showy or small, mostly snapdragon-like; calyx 4-5 toothed or parted; corolla usually Z-lipped sometimes nearly regular, tubular, 4-5 lobed or parted at apex; stamen 2, 4, or 5, B in Z sets of unequal length, on the
corolla tube; style simple or 2lobed.
Figure 39- (A) MOTH MULLEN (B) SPEEDWELL
Herbs or vines with mostly alternate leaves; flowers regular; calyx 5-lobed or parted; corolla tubular and 5-lobed or 5-parted; A
stamen 5, on the corolla tube, separate or anthers united around style; many seeded berry.
Figure 40 - (A) GROUND CHERRY (B) HORSE NETTLE
COMPOSITE FAMILY 1. (compositae liguliflorae) - Herbs with alternate or basal leaves and milky juice; flowers in involucrate heads, yellow, blue or white; individual flowers small, all alike; calyx completely adnate to the ovary, its free upper portion (limb or pappus) of scales, simple or plumose bristles or wanting; corolla tubular with a 5 notched or toothed petal-like part, (ligule); stamen 5, united in a tube around the pistil; style 1, 2-cleft; ovary 1-celled; 1-seeded; fruit an achene.
A B "C
Figure 41- (A) CHICORY (B) YELLOW GOATSBEARD
(C) PRICKLEY LETTUCE
COMPOSITE FAMILY 2. (compositae tubuliflorae) - Herbs with alternate or opposite leaves and flowers in involucrate heads but differing from the above Liguliflorae in having watery juice and ligulate flowers wanting or marginal only (then called ray flowers), the central (disk flowers) tubular only (the corolla not expanded into a ligule) pappus various, stamens around the 2-cleft style, fruit achenes.
DISK OR TUBULAR FLOWERS
Figure 42 - STRUCTURE OF HEAD OF TUBULIFLORAE
Classification by crops
1. Granineae or Grass Family: wheat, rice, barley, oats, corn,
sorghums, sugar cane, millet.
2. Leguminoseae or Pea Family: peas, beans, clovers, soybeans,
3. Liliaceae or Lily Family: onion, garlic.
4. Solonaceae or Potato Family: potato, tomato, tobacco.
5. Malvaceae or Mallon Family: cotton.
6. Compositae or Sunflower Family: sunflower, safflower.
7. Euphorbiaceae or Milkweed Family: castor.
8. Linaceae or Flax Family: flax or linseed. Classification by general use
1. Cereals: wheat, rice, corn, barley, etc.
2. Pulses: peas, beans, soybeans.
3. Oilseeds: linseed, castor, peanuts, sunflower, soybeans.
4. Fiber: cotton, jute, sisal, kenaf, flax.
5. Stimulant or Drug: tea, coffee, tobacco.
6. Root Crops: potato, sweet potato, sugar beet. Classification by specific use
On some occasions, plants are used for special purposes. We then place the crop into one of several categories:
1. Silage Crop: Any crop which is cut green and stored for
fermentation in an air tight container that is
for livestock feed.
2. Soiling Crop: Any crop which is cut green and fed immediately
3. Cover Crop: Any crop planted to produce a cover on the land
to help reduce soil erosion.
4. Green Manure -Crop: A crop, preferably a legume, which is
plowed under when green to increase the productivity of the soil.
5. Catch Crop: A short season crop planted so that a little income
is realized when the major crop has failed.
6. Nurse Crop: A crop planted frequently to help the establishment of another crop while it is young.
Classification according to life cycle
Plants may also be grouped according to their length of life. Because of this classification, plants are either "annuals", "biennials", or 11perennials".
An annual crop is one which completes its life cycle in the course
of one year. A biennial crop requires two years to grow, mature, and die, whereas a perennial crop will require more than two years.
Wheat or corn are good examples of an annual crop. , Sweet clover and beets are examples of biennial crops as they must live over winter into the second year before being able to flower. Alfalfa is a good example of a perennial crop as it has been grown for periods of twenty to twentyfive years. Sugar cane is -normally an annual, but may be grown for two or more years, in which case it becomes a perennial. Cotton may behave as an annual, biennial or perennial depending on the type of cotton and/or the climatic condition under which it is grown.
C. COLORATION IN PLANTS
The most common external characteristics. of plants and the most impressive and distinctive is color. Some of the pigments responsible for color are closely tied up with the physiological activities of the plant itself. While it is possible to find all shades and combinations of the colors in the plant kingdom, there is in general a predominance of the primary colors, green, red, blue, and yellow. These colors are imparted to the plant by definite chemical compounds or pigments, each of which has its characteristic color. The particular color which a plant organ- assumes is usually caused by the predominance of one or another of these pigments or a combination of several of them. When plants or parts of a plant appear white, it is because of the absence of these pigments.
The green color so uniformly present in plants is caused by a
pigment called chlorophyll. This -is broken down into two closely related pigments - chlorophyll A and chlorophyll B. Chlorophyll occurs in practically all flowering plants, mosses, ferns, and algae. It will develop in roots, stems, leaves, and fruits, if these organs are above ground and exposed to light. It is not normally present in the flesh of an apple nor is it usually found in underground portions such as roots or tubers. Though not visible, it may be found in red or yellow leaves, when the other coloring matters are extracted. Chlorophyll has been termed the "key to survival" of the plant and animal kingdoms. This green pigment in the chloroplasts receives thelight energy from the sun and combines carbon and oxygen from carbon dioxide with hydrogen and oxygen from water to form life-sustaining organic compounds. No other way has been found to unlock nature's elements and combine them into nourishing food.
Just how the plant manufactures chlorophyll has not been determined, but it is well known that certain conditions and substances are necessary for its formation. There must be light of proper intensity. Too much or too little is detrimental. Plants grown in total darkness do not become green. This may be demonstrated by potatoes growing in cellars, or grass growing under boards. A favorable temperature is also necessary for chlorophyll formation; excessive temperatures hot or cold being harmful. In addition, there must be an available supply of oxygen and of salts containing iron, nitrogen and magnesium. A supply of carbohydrates such as sugar is also necessary for chlorophyll formation.
Red is one of the most conspicuous colors found in vegetation. It
may be present in leaves, stems, flowers, fruits, and roots. In leaves, it may completely obscure the chlorophyll. Such an example is red cabbage. Most of the red, blue and purple colors in plants are due to a class of chemical compounds known as anthocyanins. These pigments are not contained in plastids, as is chlorophyll, but are found dissolved in the fluid content of the cell and are, therefore, uniformly distributed throughout the cell. In some cases they appear as crystals.
Several yellow pigments collectively known as carotenoids are
found in plants, and the most widely distributed of these are carotin and xanthophyll. These two pigments are generally present with chlorophyll in the chloroplasts, often giving healthy green leaves a decidedly yellow tinge. They are not restricted to the chloroplasts alone, but are also found in plastids known as chromoplasts. They are never found dissolved in the cell sap. It is the occurrence of carotin in the roots of the carrot that gives it the, bright yellow. color. The name of the pigment originated from its presence in the carrot. The yellow color of butterfat and of egg yolks is due to these pigments.
When plant parts appear white, it is because of the absence of pigments. This may be due to a physiological change of the plant or it is sometimes induced by plant nutrient deficiencies and on occasion is present in a diseased plant.
D. HOW PLANTS GROW
The body of a seed plant is made up of distinct parts known as roots, stems, leaves, flowers, fruits, and seeds. The organs are composed of various kinds of tissues, such as storage, conducting, supporting, and protective tissues. Tissues, in turn, are made up of structural and physiological units called cells.
The cell is of great importance because it is the seat of the vital physiological processe's and the bearer of the hereditary material from one generation to another. The term cell is applied to the living protoplasm. Protoplasm is generally known as the living material of the whole plant or animal body. It has been referred to as the "physical basis of life". Each typical cell contains a single body called nucellus. The body of the nucellus is composed of what is known as the nucellar gell and chromatin. Chromatin is a very important part because this thickens into bodies called I' chromosomes". The inheritances of the plant is determined by materials in these chromosomes.
The growth of plants is a process of a mature cell dividing. The smaller cells grow and enlarge until they become mature, then divide again as growth takes place. The rate of plant growth depends on several factors, among which are the rate at which food materials are supplied, the energy obtained from the oxidation of sugars, the temperature of the area, and the amount of plant nutrients available. As the plant grows and develops, cells unite and perform special functions. Some cells form a conducting tissue which is called phloem. The chief function of phloern is the conduction of foods such as sugars and proteins. Other cells form the generally woody portion, or the xylem portion of the plant. This xylem tissue is generally the water conducting and strengthening tissues of the plant.
The growth process may be said to be the division, enlargement, maturation, and specialization of cells. As these cells grow, divide and specialize, they perform the basic plant functions of photosynthesis, respiration, and transpiration.
24 HOURS GROWTH
24 HOURS LATER
WHERE GROWTH TAKES PLACE
Leaves are perhaps the most conspicuous part of plants. Being rich in chlorophyll, they are responsible for the common green color of forests and fields. They are always borne on stems and never on any other organ. The part of the stem to which a leaf is attached is called a node. The upper angle the leaf makes with a stem at its point of attachment is called the axil of the leaf. Invariably a bud is found in this axil although the bud may be so immature as to be invisible to the naked eye.
A complete leaf consists of an expanded portion known as the lamina or blade, a leaf stock or petiole by which the blade is attached to the stem, and two small appendages at the base of the petiole called stipules. When any of these parts are lacking, the leaf is said to be incomplete.
The blade of the leaf is strengthened by the presence of veins.
These veins are made up chiefly of vascular or conducting tissue which is continuous with that of the petiole. The vein serves to distribute water and dissolved inorganic salts throughout the blade and to carry away foods as they are made.
There are two principal types of venation or veining, parallel
venation and net venation. In parallel-veined leaves, the principal veins run parallel to each other from the base to the tip of the leaf. This type of venation is characteristic of the monocotyledonous plants and is especially well defined in the grasses * In net-veined leaves, the veins branch again and again, forming a complete network through the leaf.
EPIDERMIS PALISADE MESOPHYLL
TWO GUARD CELLS SPONGY MESOPHYLL
CROSS-SECTION OF A POTATO LEAF
The blades of some leaves are deeply indented at the margins.
Others are completely separated into individual parts called leaflets. As
long as the blade is in one piece, even though deeply lobed, the leaf is said to be simple. When the blade is completely dissected into leaflets, the leaf is said to be compound.
The outermost layer of cells, which extends all over the surface of the leaf, is called the epidermis. The interior of the leaf, between the upper epidermis and the lower epidermis, is called the mesophyll. The lower epidermis, and sometimes the upper, is perforated by numerous pores known as stomata or the singular verb, stoma. Each stcma is a minute opening between two highly specialized epidermal cells called guard cells.
The leaf is the center of two very important processes called photosynthesis and transpiration. Photosynthesis may be defined as the process by which green plants manufacture carbohydrates by putting together carbon dioxide, water, and sunlight. A simplified diagram of photosynthesis is shown in Figure.45 . Probably no other plant process has been more thoroughly studied. Yet, in spite of all the investigation, the exact nature of the process is still unknown. The well known facts about the process may be summarized as follows:
1. Water and carbon dioxide are the raw materials.
2. Chlorophyll is necessary.
3. Light energy is stored.
4. Oxygen is liberated.
5. Carbohydrates are formed.
Transpiration may be defined as the emission of water vapor from the internal tissues of living plants. The degree to which water is lost from plants depends on the nature of the cell wall. From tender growing parts of the plant such as the leaf, the loss of water by transpiration takes place quite rapidly. The greatest loss of water takes place from the small pores or stoma of the leaf. Beneath each stoma is an air cavity surrounded by cells which are loosely arranged. The water moves into the air spaces and passes into the outer air through the stoma. The stoma have guard, cells, the opening and closing of which is controlled by the living protoplasm. When the guard cells are highly turgid or liquid filled, the stomata are opened and transpiration is great. When the guard cells are least turgid the stomata are closed and transpiration is negligible. Transpiration is affected by the following factors:
CO FROM AIR
SOURCE OF ENERGY
WATER AND WASTE PRODUCTS
REMOVAL OF RAW MATERIALS
TAKEN FROM SOIL BY ROOT HAIRS
1 . The intensity of light.
2. The humidity of the atmosphere.
3. The temperature of the soil and air.
4. The movement of air.
5. The water content or soil moisture content of the soil.
Sometimes a comparison is made between the total amount of water transpired and the total dry weight of the plant. The value obtained by dividing the weight of the water transpired by the dry weight produced is called the water requirement of the plant. In other words, it is the number of pounds of water used by the plant in producing one pound of dry matter. (This value varies greatly in many plants as well as in the same plant under different conditions, but usually has a value of two hundred to five hundred pounds of water to produce one pound of dry matter for most crop plants growing in humid regions.) However, some plants may require as much as one thousand pounds of water to produce one pound of dry matter.
Transpiration is the elimination of water in vapor form. However water is sometimes eliminated by the plant in liquid form. This process is called guttation. Guttation generally occurs under atmospheric conditions that normally check transpiration. It is particularly pronounced on cool humid nights following hot days. The water usually forms in drops along the edges or tips of leaves where it is sometimes mistaken for dew.
Respiration is the process of taking in oxygen and giving off of carbon dioxide, for the purpose of releasing energy in plants. It is basically the reverse process of photosynthesis - carbohydrates are oxidized and broken down instead of being produced. The most important aspect of respiration is the consequent release of energy necessary for growth and maintenance-of the plant. The respiration processes are controlled by enzymes formed in the protoplasm.
Respiration goes on both day and night. During-the day photosynthesis normally proceeds at a faster rate than respiration, so that the carbon dioxide liberated in respiration is more than balanced by the oxygen liberated by photosynthesis. At night the plant gives off carbon dioxide, since respiration continues during the night, while photosynthesis ceases in the dark.
The most important functions of the stem are probably mechanical support of the leaves, flowers, and fruits, and the conduction of water, inorganic salts, and food materials. The leaves carry on the process of photosynthesis. After the foods are made, the stem again provides the pathway through which these foods are removed from the leaves, and carried to other regions of the plant. Similarlythe stem supports the flowers, fruits and seeds, and provides the conducting channels through which these organs are supplied with necessary food for development. In addition, stems sometimes serve as food storage organs in the plants. The stems of some species of plants are also used for water storage. At times, the stem also serves as a means of propagation. While most stems are erect aerial structures some remain underground, others creep along the surface of the ground, and still others are short and inconspicuous.
True stems arise from buds. They have nodes and internodes. They bear leave s,buds and sometimes roots at the nodes, and have characteristic markings such as leaf scars, bud scale scars, and lenticels. A detailed diagram of the stem is shown in Figure 46.
LIGUL - TI. AURICLE
DECURRENT )&L. SHEATH JOINT
ROOT PRIMORDIA . ROTBN
WAX RINGLEAF SCAR
GROWTH CRACK CORKY PATCH
Buds are undeveloped shoots often in a dormant condition. In
many plants the more prominent buds from which the major growth of the stem takes place are dormant during unfavorable growing conditions of late autumn and winter. At such times they are protected by a series of overlapping scales. These are called bud scales. Some buds give rise only to vegetative shoots consisting of stems and leaves. Such buds are usually called leaf buds. Others may develop flowers only. These are called flower buds or fruit buds. Terminal buds are buds occurring at the tips of branches. They are found on most plants and are often the largest buds on the plant. They usually give rise to the principal growth in the length of plants or branches bearing them. Lenticels appear on woody stems as small openings or pores. They function in the exchange of gases between the interior of the stem and the surrounding atmosphere.
Typical stems exhibit wide variations in size, form and structure. In length they vary from less than an inch to several hundred feet. In thickness ' they vary from almost hairlike structures, to trunks of trees fifty feet and more in diameter. Some stems are tender, fleshy, or watery while others are hard and woody. The classification of plants into herbs, shrubs, and trees depends on the size and woodiness of the stems. Herbs are low growing plants, the sterns of which are generally succulent or fleshy although the older ones may develop woody tissue. Shrubs and trees have woody stemsbut shrubs branch profusely near the base and do not grow as large as trees.
Stems, like leaves and roots, may appear in different forms and also perform functions in varying ways. Such deviations are widespread and numerous. Two principal deviations will be considered here underground stems and aerial stems. There are four principal kinds of underground stems:
1. Rhizomes or root stocks
The rhizome or root stock, the least modified form, is merely a horizontal stem growing beneath the surface of the soil. In some cases, it is only partly covered. Though often called roots, rhizomes are really stems, as evidenced from the fact that they consist of a series of nodes. An example is Canada thistle and quack-grass. When cut up as in plowing and cultivating, each sma.11 piece produces a new plant. This feature makes such plants noxious weeds and very difficult to eradicate.
When rhizomes become enlarged at the growing end by the accumulation of stored food, tubers are produced. An example of this is the potato. Tubers are the principal organs of food storage in plants which produce them. Potatoes are regularly propagated by cuttings of the tubers.
Corms or solid bulbs may be illustrated by the crocus. It has a very short thick rhizome or root stock. Buds are produced at the upper nodes and roots from the lower surface. The buds produce the new plant.
The bulb may be regarded as a stem reduced to a single bud
consisting largely of, fleshy leaf scales. When the leaf scales extend completely around the bulb, as in the onion, leek or tulip, the bulb is said to be coated. When numerous narrow scales do not completely encircle the stem as in the lily, the bulb is said to be scaly.
Aerial stems may be unusually long as in plants with climbing or creeping stems. Climbing stems generally are attached to some support and often climb by means of special devices. Creeping stems or stolons, trail along the surface of the ground and take root at the nodes. Examples are strawberries, white clover, and buffalo grass.
Stems also may be thornlike. Thornswhich are modified stems, usually arise in the axils of leaves. These take many forms and shapes and can be dangerous, uncomfortable and poisonous.
The root is the part of the plant body which ordinarily grows downward into the soil, anchoring the plant, and absorbing water and inorganic salts in solution. Roots are not necessarily underground structures. The 11prop roots" of corn and the "air roots', of orchids are examples of true roots that normally remain partly or completely above ground. Unlike stems, roots do not bear leaves and buds and are not divided into nodes and internodes. For this reason, roots usually branch in an irregular manner. Roots, under certain conditions, develop adventitious buds which give ise to leafy shoots. Such shoots are produced very irregularly and often in profusion when the roots of plants like poplars, black locust, and apple are exposed or near the surface of the ground.
Roots are used by different kinds of plants in many ways but the functions of most roots are: absorption, conduction, anchorage, and storage.
Perhaps the most important function of roots is the absorption of
water and inorganic salts. Since the higher plants grow almost exclusively
on land, it is necessary for them to be in direct contact with the supply of water and inorganic salts that exists in the soil. Only the youngest roots of the plant are ordinarily concerned in absorption. Trees must constantly develop new roots if absorption is to continue.
Once these materials are absorbed from the soil, the root serves to pass them on to the stem. The xylem of the root is continuous with that of the stem. By this means, water and inorganic salts can be distributed throughout the plant.
While it is important to ha ' ve a part of the plant in contact with the supply of water and inorganic salts, it is also important to have other parts placed to receive light and air. This is accomplished in many plants by upright stems and spreading branches. Roots support the stem by anchoring it to the soil. A deep rooted plant can serve this purpose better than a shallow rooted one. Tap rooted trees more readily withstand heavy wind than do surface rooted plants.
In most plants, part of the food manufactured above ground is carried to the roots and stored there for future use. Such storage is particularly found in biennial and perennial plants. Biennials like the beet and cabbage, usually develop a rosette of leaves during the first year of their growth. During this period large amounts of food are made and stored in the roots. The following year the stored reserves are used to develop an upright shoot on which flowers and seed are produced.
Very often roots become large and fleshy as the result of food storage. This is true of sweet potatoes, radishes, beets, turnips, and many others. The internal structure of such roots becomes highly modified to accommodate the stored reserves. Many of these plants are of considerable economic importance.
Since many roots are capable of developing adventitious buds which give rise to leafy shoots, roots are sometimes a means of propagation plants. This is called asexual reproduction. This enables man to propagate many forms of plants that otherwise might be difficult to reproduce. Sweet potatoes are regularly grown from root cuttings just as the white potato is grown from tuber or stem cuttings. Some plants, when cut off at the roots, develop adventitious buds which give rise to new plants. This phenomena is sometimes utilized in the propagation of roses and other plants.
Roots can be classified as primary roots, secondary roots, and adventitious roots. They may also be classified as tap roots, fibrous roots, and fleshy roots.
The root that is first put- out by a germinating seed usually grows directly downward and is known as the primary root. The branches from this primary root are called secondary roots. Secondary roots originate much farther from the root apex than do primary roots.
Many grass stems root at the nodes or joints if the stems become prostrate. Such plants as the geranium, carnation, willow, poplar and rose will deve ' lop roots if placed in moist sand or water. All roots so developed are to be classed as adventitious roots. In the cereals, adventitious roots develop at the junction of the root with the stem. Sometimes the first nodes of the stem start the principal roots of the plant.
If the primary root remains the largest root of the plant and continues its growth to become themain. root, it is known as a tap root. Rag weeds, burdock, dandelion, oak and hickory trees all have well developed tap roots.
Monocotyledonous plants usually do not develop tap roots. When numerous long slender roots of about equal size are developed they are known as fibrous roots. In this case no one root is the largest. Many grasses have fibrous root systems.
Recent studies have shown that the extent of root development is much greater than former 'knowledge seemed to indicate. In many cases the roots are longer, more extensive and greater in weight than the tops of the same plant. A single corn root for example has been found to occupy 230 cubic feet of soil. The species of plant in itself is important. Many plant roots penetrate three, four, or five feet. Alfalfa occasionally has roots extending to a depth of 40 to 50 feet into the soil. Numerous environmental factors determine the direction and extent of growth. These include gravity, light, temperature, soil texture, soil minerals, oxygen supply, and moisture. Every root is subjected to all of these' factors. The actual growth of the root is the result of the action of these factors.
In response to gravity, roots generally tend to grow downward.
This is known as positive geotropism. If subjected to one-sided illumination, roots grow away from the light and exhibit what is known as negative phototropism. Roots will bend in the direction of the temperature most favorable to their growth, exhibiting what is termed as positive therm6tropism. Roots develop best in a loose fertile soil.
Oxygen must be available for the respiration of roots. Experiments on a number of plants show that growth ceases when oxygen is removed. Roots at great depth in the soil, in waterlogged soils, or in very compact soils are likely to suffer from lack of oxygen.
Roots do not seek water but will continue to grow in the direction of moisture supply. Moisture is an important factor in determining direction, depth of penetration, and lateral spread of roots. In desert regions annual plants seldom penetrate more than a few inches with the greatest development in the upper two or three inches. However, where rainfall is great and where much of the rain infiltrates into the soilroots will penetrate much deeper.
Structure of roots'
When seeds are germinating the first structure to emerge from the seed is the root. Roots of this kind are usually white or colorless, more or less rounded off or pointed at the tip. Figures 47 and 48 are drawings of a root tip illustrating the root hairs. The tip itself is covered with a thimble-like tissue known as the root cap. The root cap is a distinctive root structure found on practically all roots but never found on any other plant organ. It is a loose tissue acting as a cap or protective layer for the growing point of the root.
Behind the root cap will be found a multitude of fine white hairs
radiating outward from all sides of the root. The shortest root hairs are nearest the root cap. Farther back they increase in size until the maximum length is reached. The area covered by these root hairs is known as the root hair zone. Beyond this narrow zone no hairs are visible. Near the root apex, new hairs are continually being produced. In the older r-egion of the root hair zones, the hairs are dying and disappearing. The root hair zone is constantly moving forward keeping pace with the growth of the root point or apex. Root hairs grow until they come in contact with some solid substance such as a soil particle and then flatten out, thus presenting the greatest possible absorbing surface coming into intimate contact with the film of moisture which surrounds the soil particle. As a result of this response, the -root hairs assume irregular forms, clinging tightly to the soil particles. It is almost impossible to remove a plant from the soil without leaving behind most of the root hairs. For this reason, plants pulled out of the soil and transplanted usually wilt, unless the transpiring surface is reduced by pruning or cutting back. The actual size and the amount of production of root hairs depends upon the conditions under which they are formed. The kind of plant, temperature, moisture, oxygen supply, and the concentration of various minerals in the soil solution are important factors. A slow growing root usually has a greater density of root hairs per unit area than does a fast growing root. A saturated soil generally suppresses root hair development. Most plants develop root hairs best in a well aerated moist soil.
Most roots are normally underground structures. In certain species of plants they are found partly or entirely above ground. These are spoken
REGION OF CELL ENLARGEMENT
REGION OF CELL DIVISION
LONGITUDINAL SECTION OF A YOUNG BARLEY ROOT
ROOT EPIDERMAL CELL
SHOWING ROOT HAIR PROTRUDING
of as aerial roots, When the stems of corn have started to grow rapidly, the first few nodes above the soil send out a: cluster of stilt-like roots to the soil. These roots help to support the tall stem but they also grow into the ground and function in absorption of water and inorganic salts. Roots of this type are called prop or brace roots.
The climbing roots of plants such as poison ivy, english ivy, etc. , are also a form of aerial root.
Of the various materials the plant gets from its environment, none is more important than water. Plants are composed of from fifty to eightyfive percent water. Plants are constantly losing large quantities of water by transpiration. This water must be supplied through absorption by the roots if wilting of the plant is to be prevented. Water is the medium by which foods are transported from one part of the plant to another. Without a constant supply of water the plant could not carry on any of its physiological activities.
Water does not exist in a pure form in soil but is a solution containing various solutes, clay particles, dissolved nutrients, etc. This water in the soil is referred to as the soil solution. The osmotic pressure of the soil solution averages from . 2 to 1 atmospheres of pressure in humid regions.
By means of tiny root hairs, the plant receives water and nutrients from the soil by the process of osmosis. As the water is absorbed by the root hairs the cells in the root hairs tend to become more and more turgid. As this pressure rises, water passes from one root hair cell to another. This cell in turn passes it on to the next cell by osmosis and so on until it reaches the xylem. Through the xylem, the water is carried to all parts of the plant. Thus the relationship of the root to the stem, the stem to the leaf, the leaf to the flowering parts or seed producing portion of the plant is seen. Each in turn has a definite function to perform. This enables the plant to act as a factory in converting minerals and moisture from the soil and carbon dioxide from the air into food which will enable humans and animals to live more abundantly.
Roots growing in the soil have important eff ects on the chemical and physical nature of a soil.- The decay of roots furnishes available nitrogen and other substances for later crops. By this means, considerable amounts of organic matter are added to the soil each year. This organic matter influences both the physical and chemical properties of the soil.
The flower is the structure concerned in the sexual reproductive processes of plants. Flowers lead to the production of fruit and seed.
Flowers may be composed of as many as four different sets of organs which are: sepals, petals, stamens, and pistils. When all four sets of organs are present, it is called a complete flower. If any one of these sets of organs is lacking, the flower is said to be incomplete. If the flower lacks either stamens or pistils, it is said to be imperfect. When both the stamens and the pistil are present, the flower is said to be perfect, regardless of whether sepals or petals are present. Therefore, all complete flowers are perfect. Incomplete flowers may be either perfect or imperfect, depending upon whether or not both stamens and pistils are present. In the case of imperfect flowers, stamens alone may be present in one flower and pistils alone in another flower on the same plant. These flowers are unisexual and the plant is said to be monoecious. If the male or staminate flowers are produced on one individual plant and female pistillate flowers on another, the species is said to be dioecious. Monoecious I species are much more common. An example of this species is corn. Occasionally a flower forms with no stamens or pistils. Such flowers are said to be sterile and never produce seed.
. . .
OVARY * OVULES
Sepals and petals, or at times sepals alone, constitute the perianth. These parts are frequently spoken of as accessory flower parts. They are not essential to seed formation. Stamens and pistils are regarded as the
only essential organs of the flower. Both must be present, either in the same or in different flowers, in order to have sexual reproduction and the resulting formation of seed. The stamens are the male portion of the flower. Each stamen consists of a stock or a filament bearing an anther. The anther produces the pollen.
The pistil is the female portion of the flower. The enlarged basal region is. called the ovary. The ovary Produces the ovules. The apex is known as the stigma, and that portion connecting ovary and stigma is known as the style. The function of the stigma is to receive the pollen grains carried to it by various agencies such as wind, insects, gravity, and so on. When the pollen grains are shed from the anther, they reach the stigma of the same or of another flower. This transfer of pollen from anther to stigma is known as pollination. In the case of imperfect or unisexual flowers, the transference of pollen from the anther of one flower to the stigma of another occurs. This is called cross-pollination. Perfect flowers, or flowers which have both male and female parts, are generally self -pollinated, that is pollen transferred from anther to stigma on the same flower.
The time that elapses between pollination and fertilization varies
in different species. It could be less than 24 hours or extend over a period of several months. Most frequently, it takes from two to five days.
A seed has been described as a plant that is packaged for shipment. Above all else, it is a way of survival of a species. Seeds are a vehicle for the spread of new life from place to place. Seeds are food for man and animals. They are wealth and a never ending source of wonder.
One of the factors involved in crop production over which a farmer has considerable control is the choice of seed. He has the ability to choose seed of a proven variety and one which is pure and free from insects or plant diseases. A poor seed choice results in bad yields and an economic loss.
Good seed characteristics
The seed a farmer chooses should have the following characteristics:
1. It should be pure and free of varietal mixture.
Z. It should germinate rapidly to give strong vigorous seedlings.
3. For the variety, the seed should be large and plump.
4. There should be absolutely no noxious or objectionable weed
5. It should contain no insects, insect eggs, or disease spores
in or on the seed.
6. The seed should be uniform in size.
7. It should be free of rocks, chaff or trash.
In order to germinate, seeds must have proper amounts of
temperature, moisture, air, and sometimes light. If any of these conditions are not, right, a seed will lie dormant and not germinate. When the farmer sows his seed, he wants to be sure that it will germinate and produce a good stand.
Many seeds have a built in, delayed-action mechanism that insures the seeds will remain dormant until the proper conditions for germination have arrived. The nature of this dormancy varies greatly among plants. It can be due to a moisture resistant "hard" seed coat. Some seeds must go through a long period of cold temperatures before they will germinate. Other seeds will lie dormant in the soil until they are exposed to light. Some will fail to germinate immediately after they are separated from the mother plant because they are not completely mature. Dormancy in seeds may protect them, but it can be a problem in commercial production when quick, vigorous germination at the time of planting is desirable.
One way to estimate the kind of stand obtainable in the field is to run a germination test. To do this, a representative sample of seeds is taken from the lot to be sown. These seeds are placed under conditions of good aeration and abundant moisture for a few days until the embryo has had a chance to expand. The seeds that have germinated are counted and the percentage calculated.
Attention should be'paid to the vigor of seedlings. Vigo rous
seedlings that germinate rapidly and have thick hypocotyls and healthy primary root systems, are less likely to succumb to seedling diseases.
All seed from the United States and a number of other countries
must be labeled with certain information. This is for the protection of the buyer so he knows what he is buying., The information usually contained on the tag is:
1. Name of each kind of agricultural seed in excess of five percent.
2. Percent of other crop seeds.
3. Percent of weed seeds.
4. Name and approximate number of noxious weed seeds.
5. Percent inert matter.
6. Percent germination.
7. Month and year of test.
8. Name and address of seller.
9. Lot number.
Whenever seed is discussed, the word "certified" always comes up. What is "certified seed"? It is seed of a known genetic identity. This is accomplished by a system of records and inspection. Pedigree records are kept of the planting stock used. Inspections are made in the fields and during all phases of production, harvesting, and cleaning. Each bag is sealed and tagged with a certification tag after it is tested and meets the requirements for purity and germination. Without such a system, varieties tend to become mixed and contaminated and lose their identity. Through certification, it is possible to buy seed from many sources, move it all over the world, and still be certain of having the variety marked on the label.
Choice of good seed alone, will not guarantee good crop yields and high quality produce. Regardless of how good the seed is, if it is planted too early, too late, too thick or too thin, maximum potential will not be realized.
Each crop should be planted at that time of the year when the different stages of its development will be most accurately correlated to the most favorable weather conditions. Temperature and moisture are of special importance, while in many species light and day length play an important part. Control of weeds, plant diseases and insect pests should be kept in mind when selecting planting dates. Although not always true, the earlier a crop is planted without danger of frost damage, the better it will perform.
High yields are dependent upon good vegetative development of the plants prior to the beginning of maturation and seed development. Therefore, the longer the period of vegetative growth, the higher the yield.
Soil moisture at seeding time should be ideal for plant emergence.
As the season progresses, soil moisture declines, especially in the surface layers. As a result, later seedings must often be planted deeper than earlier ones. There is a limit to how deep a seed may be placed. In general, it is not wise to bury seed more than three or four times their diameter. Small seeds, therefore, cannot be planted as deep ly as larger one s.
Temperature, on the other hand, becomes more favorable as the season advances. With the high moisture level and low temperatures of early spring, low oxygen also prevails. Many seeds tend to rot under these conditions. Planting dates must be delayed until the soil is warm enough to insure rapid germination.
Rate of planting is especially critical for row crops. With broadcast crops, like small grains, tillering is more prevalent when seeding rate is low and tends to compensate for the lowered rate. Degree of tillering is also influenced by soil fertility. For crops that tiller freely, it is generally recommended that seeding rates be higher on poor soil. For crops like corn, beets, and potatoes which do not tiller, higher seeding rates would be recommended on the fertile soils. Corn planted at higher rates, produce smaller ears but higher yields.
J. VEGETATIVE REPRODUCTION
Plants may be propagated in two general ways; by seed or vegetatively. In most farm crops the use of seed is the most economical and efficient way. With a few crops, however, reproduction by vegetative means is necessitated since seedlings are not always true to type and some seed cannot be produced or harvested economically.
Crop plants produced vegetatively or asexually, and the plant part used to propagate them, include the following:
I . Roots - sweet potatoes, cassava, kudzu.
2. Tubers - potatoes, Jerusalem artichokes.
3. Stolons - Buffalo grass, Bermuda grass.
4. Rhizomes - Bermuda grass.
5. Stems - sugar cane, Elephant grass, cassava.
Cuttings of stems and tubers should be made in such a manner that enough buds or eyes are available for ample vegetative growth. Care should be taken so that the seed stock is not buried too deeply.
K. WEED CONTROL
A weed is generally defined as any plant that is out of place. The chances of a farmer losing his entire crop to weeds is relatively remote, nevertheless, weeds cause a great deal of damage each year.
The chief losses caused by weeds are:
1. Reduction in yield due to competition by the weed for needed*
light, water, and mineral nutrients.
2. Decrease in crop quality.
3. Costs of weed control.
4. Losses due to disease and insects harbored and protected by
5. Decrease in land value.
6. Increase in taxes necessary to support county and state
Most weeds are relatively easy to control. Some weeds, once
established, are extremely difficult to keep in check. These latter species are frequently termed noxious weeds. The plant is removed from the 11noxious" list only after an effective control measure is developed.
The ideal method of weed control is to prevent their establishment. Once weeds are established, they can be combatted throughmechanical means such as hoeing, cultivation, and clean tillage; through ecological methods such as crop competition; and through chemical methods of control. The method of control used would depend on the species of weed and the nature of environment. In most cases, a combination of methods gives the best results.
The key to prevention rests with the ability to identify the weeds as seeds, seedlings ., and as mature plants. Whenever uncertified seed is purchased, it should be thoroughly examined for the presence of weed seeds, especially noxious weeds. If any species of weed seed is found which is not already present on the farm, the seed should be rejected
unless it can be recleaned prior to use. Equipment such as combines should be thoroughly examined before coming onto a farm. Hay should be examined for weed content before it is purchased.
In most cases, eradication of a weed species is not economically justified. This would be true of small relatively harmless weeds or one that is already widely established on a farm. It would not be true of a noxious weed not yet well established.
Listed among mechanical methods of weed control are hoeing,
pulling, intertillage, blind tillage, clean tillage, smothering with water and mulches, and controlledburning.
Timeliness is an important consideration in mechanical weed control. Cultivation of some annual weeds should be done as early as possible, sometimes even prior to emergence. With some perennial weeds, multiple tillage is required. To help reduce the food reserves in the roots, the plant may be allowed to emerge and grow for about two weeks, depending on the species and environment, and then destroyed.
Ecological control methods have not been recognized by man until recent years. These methods include crop competition and biological control.
In very recent years, inexpensive chemicals have cut the cost of
controlling weeds in some crops to a small fraction of former costs. The most spectacular of these has been 2, 4-dichlorophenoxyacetic acid commonly called 2, 4-D. Although 2, 4-D is relatively new, chemical weed control is not. Until recently, however, chemical weed control was too expensive to be widely used on a field basis.
Chemical weed killers may be classified under two hea-lings: nonselective and selective. The non-selective herbicides are chemicals which are toxic to all plants. Selective herbicides on the other band, are chemicals which destroy one type of plant without seriously injuring another r.
Some species of plants are more susceptible to injury by any
specific herbicide than'are other plants. Because closely related plants are similar to each other morphologically and physiologically, members of the same botanical family tend to be either susceptible or tolerant to a given herbicide.
The number of effective chemical compounds used to control weeds is constantly increasing as testing of herbicides continues. As the numbers
increase, the decision becomes more difficult in selecting the most effective chemical. In most cases, technical advice should be sought. L. PLANT DISEASES
Any abnormal condition in the growth or development of a crop is called a plant disease. Although some of these abnormalities are caused by environmental factors, most are caused by living agents which parasitize the plant.
Various external signs and symptoms indicate the presence of a plant disease. Some of the most common are:
2. Perforated leaves
4. Necrosis, or the death of some plant tissue
5. Dwarfing or atrophy of plant parts
6. Increase in size, or hypertrophy, of plant parts
7. The replacement of plant organs by new structures
8. Complete destruction of some of the plant organs
10. Alteration in plant habit or symmetry
11. Dropping of leaves, blossoms, fruits or twigs
12. Production of excrescences and malformations, such as
galls, cankers, rosettes, etc.
13. Production of an exudate
14. Rotting of a tissue
The organisms which incite plant disease can be-classified under six headings: viruses, bacteria, fungi, algae, protozoa, and nematodes.
Plant diseases reduce the value of crops by reducing yield per acre, reducing quality, or by making the plant more susceptible to other kinds of injury, such as winter killing.
Control methods for plant diseases include: use of only certified seed, crop rotation, plant breeding and use of chemicals.
Preventative methods of plant disease control have been used effectively in several countries during recent years. The principle is simple, easy to put into operations economical and effective. These countries inspect plants coming into the country and examine them for disease symptoms. Many plants must be grown for two years under quarantine for possible disease symptoms not readily detectable. The use of certified seed is one of the surest guarantees a farmer can have that the seed or plant propagules brought onto his farm will be free from plant disease.
If diseases are soil borne, the most effective way to control them is by crop rotation. By planting a crop which is not susceptible to the disease, the causative organism is reduced in numbers. A lesser amount of the disease occurs the next time the s ' susceptible plant is grown. New chemicals are constantly being tested for effectiveness as soil fumigants. With the development of'such fumigants, it is becoming possible to control soil borne diseases without crop rotation. This enables a farmer to specialize in one crop.
Plant breeding is a successful tool in controlling plant diseases in crops in which a variation of resistance to the disease exists. Plant breeding is especially successful in combat ing diseases caused by viruses, bacteria, and fungi. When a disease resistant variety is produced,. farmers have not only gained the protection against the economic loss the disease can cause, but have also saved the cost of using fungicides as well.
The exact nature of disease resistance in plants is not known. In some cases the resistance may be due to morphological adaptations of the plant: size and location of the stomata, presence of hairs, thickness of the epidermal cells, etc. In other cases, it may be due to physiological adaptations, i. e. , substances which are toxic to the disease organisms.
Whether or not a plant becomes diseased will depend on certain factors of environment, such as the abundance of the diseased organism, humidity, temperature and wind. Frequently, plants may escape the disease even though they are susceptible to it.
Many different chemicals are used to control plant diseases. Some are made to be applied to the plant, while others are applied to the soil.
Seed and f oliage- application chemicals have been quite effective in controlling diseases, especially those caused by fungi. Soil fumigation has only recently been developed but is proving very effective against nematode s.
In general, plant diseases can be classified by the causative organism. A crop disease is usually caused by either a virus, a bacteria, or a fungi. Very rarely are diseases caused by algae or protozoa.
CHAPTER III - ENTOMOLOGY
The protection of farm crops from destructive insects is one of the most important requirements for successful farming. From the time the seeds are planted, throughout the period of the growth of the plants, and even after the crop is harvested, insects cause an economic loss. Different crops vary in their susceptibility to insect damage but none entirely escape attack. Insect damage may result in total crop loss. This loss may even exceed that loss indicated by poor stands, unthrifty growth, reduced yields, or poor quality.
Such insects as the grasshopper, or "locusts" as they are called in the eastern hemisphere, boll weevils, corn borers, etc. , are quite familiar to a lot of people because of the spectacular damage they cause. In addition to this type of insect outbreak, there is the continual drain on practically all crops caused by lesser and more obscure forms of insects whose work may be unnoticed, such as root infesting insects and sap sucking species.
The larger, more conspicuous insects such as armyworms, cutworms, and beetles, as well as signs of their work, are quite familiar to most people. The injury caused by the minute forms are often mistaken for such things as poor seed, unfavorable soil conditions, or plant diseases. It is now known that many serious plant diseases are carried and spread by insects.
Agriculture in general favors the multiplication of insect pests because many farm crops are not native to the area in which they are grown and have not developed an immunity to the particular pest. Another important reason for the growing seriousness of the insect problem is the introduction of injurious species from abroad. The increased volume of commerce from abroad and the speed of airplane travel has greatly increased the possibility of accidental introduction of insects.
Man's survival depends, to a certain extent, on some insects. Insects produce honey, silk, shellac, various dyes and drugs, and are responsible for the direct production of much of our food products. There would be little tree-fruit without the aid oi insect pollinators. Over fifty varieties of vegetables are dependent upon insect pollination. Most of our fresh water fish would disappear if insects were to vanish. The majority of insects are beneficial to the farmer.
Successful insect control depends first of all upon a knowledge and understanding of the insects themselves. Each insect species or closely related group has its own characteristics and habits. These characteristics and habits have a great deal to do with the success encountered in controlling them.
B. INSECT CLASSIFICATION AND STRUCTURE
Am insect belongs to a large group of animals characterized by a body divided into three parts: head, thorax, and abdomen. They have three pairs of jointed legs, one pair of antennae and from none to two pairs of wings.
Other classes of animals mistaken for insects due to certain similarities are,
1. Class Arachnida - Spiders, ticks, spider mites, etc. These are
characterized by having only two main body parts and four pairs of
jointed legs. They never have wings or antennae.
2. Class Crustacea - Lobsters, crayfish, sow bugs and pill bugs.
This class is characterized by having five or more pairs of jointed
legs, are wingless and may have two pair of antennae.
3. Class Chilopoda - The centipedes. This class of animals is characterized by having many body segments. Each of the body segments, with the exception of the head, has one pair of legs. They have one
pair of antennae but the wings are absent.
4. Class Diplopoda - The millipedes. Millipedes are characterized
by having many body segments, each with two pairs of legs. They have one pair or no antennae and wings are absent. Millipedes are
,rarely considered a pest.
Because many insects are beneficial and others are of little economic importance, it is essential that they are correctly identified. Common names vary from place to place and with conditions. For this reason, scientific names are used by entomologists. Proper identification is also important because chemical control may vary with certain closely related species.
Instead of an internal skeleton made up of bones, the insect has an
external or exoskeleton. This cuticle or exoskeleton has an outside waxy or oily layer which helps to make it waterproof. This oily or waxy layer plays a part in the control of insects. When an insect walks over a surface sprayed with a contact insecticide, the oil on the surface of the cuticle dissolves some of the insecticide deposit from the surface. This dissolved insecticide is then absorbed through the cuticle of the insect and into the body fluid and the insect is poisoned.
The insect respiratory system is unlike that of the warm-blooded
animals. It is a series of tubes which run to various organs of the insect's body some of which open to the outside. Fumigants used to kill insects enter the insect's body through these spiracles. Other control agents such as oil, may plug these spiracles and actually smother the insect.
Insects have several different types of mouthparts. The type of
damage done by an insect pest depends upon the type mouthparts the insect has. These mouthparts are divided into five different categories: chewing, piercing- sucking, rasping, sucking, and lapping.
Insects with chewing mouthparts have a pair of mandibles or jaws which move laterally and can actually bite or chew holes in plant leaves, stems or other parts. Examples of insects with chewing mouthparts are various caterpillars or larvae such as cutworms, armyworms, corn earworms, gras shoppers, and beetles.
Some classes of insects have a sharp beak or needle-like stylet with
which they pierce the tissue of plants or animals. These are called piercingsucking mouthparts. Plant feeding insects of this type suck out the plant sap or juices and may inject a toxin during feeding which cause characteristic symptoms on the plant. Some of these insects may also carry organisms which cause disease, usually viruses. Examples of insects and related animals with piercing- sucking mouthparts are the aphids, leafhoppers, mealybugs, squashbug, fleas, mosquito, etc.
Insects with rasping mouthparts injure the surface of the epidermis of the plant by breaking the walls of the surface cells and allowing the cell content to escape. These insects then suck up the 'cell sap. This can occur on the leaves, on the flower, or on the surface of the fruit, spoiling the market quality and causing the leaf to curl. Insects with this type of mouthpart are the thrips.
Insects with sucking or siphoning mouthparts are incapable of piercing plant or animal tissue. They merely suck up liquids which are readily available from the surface of the plants or the nectaries found in flowers. Examples of insects with this type of mouthpart are the adult moths and butterflies.
Lapping mouthparts are characterized by being broad and sponge-like. These mouthparts are used for sponging or lapping up liquids and transferring them to the mouth of the insect. Typical examples are adult flies, bees, ants, and wasps.
Because insects may cause damage during only one stage of their life
cycle, a knowledge of the life cycle of insects is important. Insecticides might also be- effective during only one stage of the life cycle.
In the majority of insects, there is a change or transformation that
takes place before the adult stage is reached. This is called metamorphosis. If no marked changes occur in body form, metamorphosis is said to be gradual or incomplete. The young resembles the adult in body form but may differ in
coloration, presence-of wings, spines, or body ornamentations. Thes'6"types of insects are said to have three life stages; the egg, the nymph and the adult.
If the insect passes through marked changes so extreme that the habits and appearance of the young are radically different from those of the adult, it ,is called complete metamorphosis. Immature insects of this type are known as larva. Common names usually given them are worms, caterpillars, grubs, and maggots. Insects having the complete type of metamorphosis have four life stages; the egg, the larva, the pupa, and the adult. Insects with complete metamorphosis feed in the larval stage but may or may not feed in the adult stage. They never feed in the egg or pupal stage.
Reproduction in insects is very similar to the reproduction of animals. Exceptions are: aphids, certain weevils and other insects who produce young without mating. In some species there are no males.
The ability to produce many eggs and young in a very short life cycle
makes it possible for the insect population to build up very rapidly. A common housefly can lay about 900 eggs in her'lifetime.
D. INSECT CONTROL
With the tremendous reproductive potential, it is apparent there must be various regulating factors to keep the population reduced. Some of these factors are the natural physical factors of cold, heat, rain, and wind. Insects are killed by various diseases caused by fungi, bacteria, virus, and other organisms. Various predators such as birds, fish, frogs, etc. , as well as other insects and spiders, effect what is called natural control. When one or the other of these factors breaks down, insects build up and man must step in with chemical insecticides or some other means of control in order to prevent damage to his crops.
There are hundreds of different kinds of insecticides on the market. These insecticides kill insects by several different modes of action. Some kill by contact, others by stomach poison action, others kill by fumigation. Some insecticides are systemic in action. When sprayed upon plants or around the roots of plants, they are absorbed into the plant and translocated to the stems, branches, leaves and fruit of the plant. When an insect sucks the juices from the plant, it obtains some of the insecticide and is killed.
An insecticide, however, must only destroy the insect. It must not be harmful to the plant, animal, or man. Frequently, there is only a narrow margin of safety between toxicity to the insect and toxicity to the plant or animal. The use of these chemicals on foliage and food crops may result in residues on the feed or food products which may be harmful to animals and man.
The ideal insecticide should not destroy beneficial insects or invertebrate predators and parasites of insects. Sometimes the control of one pest favors the reproduction of another because of the destruction of their natural enemies. Other desirable features of an insecticide are availability, low cost, noninflammability, ready miscibility, and ease of application.
Insecticides are divided into five general groups and are illustrated in Table 3.
It should always be kept in mind that insecticides are poisonous;
Certain precautions should always be taken when using them. - When applying the more toxic compounds, certain articles of protective clothing should be worn. Many of the more volatile and synthetic organic insecticides are readily absorbed through the skin. Persons handling such compounds should wear clothing which covers as much of the body and head as possible. Rubber gloves should be worn when handling insecticide concentrates or when spraying with the toxic compounds. Rubber footwear should be worn to protect the feet. Since vapors, fine droplets, or dust particles of these insecticides may enter the body through the respiratory system, a'proper respirator should be worn. Hands should be washed thoroughly with soap and water e I ery time you fill the sprayer or duster with pesticides. Empty containers should be completely destroyed so they are not used for any other purpose. Pesticides should be stored in a safe place out of reach of children, pets, or persons who are not familiar with them.
Mode of Action
Toxicity to Warm Blooded Animals
Chlorinated Contact Low to DDT - DDD
Hydrocarbons (stomach) high Toxaphene
Organic Contact Low to Malathion
Phosphates systemic extremely Phosdrin
stomach high Parathion
Carbamates Contact Low to Sevin
Inorganic Stomach High Lead arsenate
(fumigant) Calcium arsenate
Botanical Contact - Low Pyrethrun
stomach Low Ratenone
Stomach High Nicotine
E. COMMON CROP INSECT IDENTIFICATION
We live in a world with teeming millions of insects - some useful and
some harmful. There are about 686, 000 known species of insects. Some of
the more common useful insects are honeybees, dragonflies, damselflies,
wild bees, robberflies, tiger beetles, ladybeetles, silkworms, etc. Insects,
of course, can be both harmful and useful. There are many more harmful
than useful types. The following Table is a list of the more common insects
which are harmful to crop plants.
Diagram of Adult Damaging Stage Crops
Insect Size and Color Size and Color Eating Habits Attacked
2" sulphur yellow 1-" dark green
Alfalfa Chews, strips Alfalfa, other
Caterpillar foliage legumes
3/4" pale brown Larva 3/4"
Chews foliage Alfalfa, clover Alfalfa cover plant soybeans
Webworm - with silken web
1/8" brown to black
Larva 1/8" green
Alfalfa Weevil (Hypera" postica)
Chews on stems, leaves, and buds
Alfalfa and clover
Diagram of Adult Size and Color
Damaging stage Size and Color
pale brown ("
2" brownish gray
Armyworm (Cirphis unipuncta)
Angoumois Grain Moth (Sitotroga cerealella)
Chews foliage strips plants
1/8" brownish gray
Corn, grains, grasses
white larva 1/8"
Chews bean fruits and cowpeas
1/5" black with white wings
vile odor when adults are crushed
Sucks juice from plants. Attacks leaves and plant base.
Beans and cowpeas
Corn, small grains, grasses, sudangrass,
1/5" white with brown head
__ _II _ __ I
1/6" brown no wings
1/6" white with brown head
Granary Weevil (Sitophilus granarius)
(Aphids) (Toxoptera GRAMINUM)
Several species various colors
Eats, chews foliage
Sucks plant juice
Small grains, corn, grasses
He s sian Fly
Sucks juice from plants causing lodging
Wheat, barley, rye, grasses
Diagram of Adult Damaging Stage Crops
Insect Size and Color Size -and Color Eating Habits Attacked
1/8" pale green
Leafhopper Sucks juices General plant
causes hopper feeder burns
" reddish brown " white grub
and black with white head
Corn Adult chews Corn, small
Billbug foliage, larvae grain, rice
feed on roots
yellowish-brown moth 1"
1" flesh color
Corn Borer (Pyrausta nubilalis)
Larva chews into stalks and ears, causes
Corn, sorghum, sudangras s
11" yellowish green 1-" varies from or gray green to black
Corn Chews corn Corn, tobacco,
Earworm ears, tobacco, cotton, tomato
armigera) cotton bolls
Diagram of Adult Damaging Stage Crops
Insect Size and Color Size and Color Eating Habits Attacked
Corn Root Sucks juice Corn, cotton,
Aphid from roots grasses, weeds
," yellowish green " yellowish white
Southern Chews into Corn, small
Corn o stem and grain, grasses,
Rootworm o feeds on roots cucumbers
" snout beetle " white with
yellowish black brown head
Cotton Chews cotton Cotton
" pale green to yellowish brown
Lygus Bug Sucks sap Alfalfa, cotton,
blasts floral beans, sugar buds beets
Diagram of Adult Damaging Stage Crops
Insect Size and Color Size and Color Eating Habits Attacked
1" dark gray
Sweet Clover Weevil
Chews stems, buds, leaves (crescentshape)
Chews on stem near node
(causes knots and weak stem)
3/8" wasp-like black
-,, yellowishwhite, brown head
Chews upper stems
Small grains, grasses
Grub chews roots, beetle chews tree foliage
Corn, grasses, grains, oak trees
Diagram of Adult Damaging Stage Crops
Insect Size and Color Size and Color Eating Habits Attacked
, yellowish brown
Chews seed and stem below ground
Corn, small grains, grasses
CHAPTER IV - CEREAL CROPS
RICE (Oryza sativa) -1/
Rice is a leading cereal crop in many countries and is' grown on all continents. It is the principal staple food in the diet of more than half of the world's population'. About 90% of the world's rice crop is grown in Asia. Outside of Asia and adjacent islands, important rice-producing countries include Brazil, Colombia, and Peru in South America, Egypt and Malagasy Republic in Africa, the United States and Mexico in North America, Italy and Spain in Europe, and Australia. Although the United States produces less than 2% of the annual rice crop, it is the leading exporter of rice since over half of the production is exported. Rice is an ancient food plant of the Far East and dates back at least to 3,000 B.C.
Rice often is considered a tropical crop but it is grown
in both the temperate and tropical zones in Africa, Asia, North America, Oceania, South America, and in the southern part of Europe. Rice yields generally are much higher in temperate than in tropical zones because of differences both in climate and in cultural practices including varieties grown. However, new high-yielding varieties and improved cultural practices developed by International and In-Country Research Stations have shown that high yields also are possible in tropical zones.
The rice crop is unique in the ability of its seed to germinate in water and the plants to grow on flooded soils. However, rice seeds usually will not germinate if covered by both soil and water. Rice may be grown as irrigated or lowland (wetland) rice, or as upland rainede) rice which is not irrigated. The two general types of production require different cultural methods. In developed countries where grain yields are rather high, most rice is grown under controlled irrigation. Several systems of controlled or uncontrolled irrigation are used in various countries to supply the needed-water for proper growth of the rice plant.
Considerable rice is grown on up land soils but this type of culture usually is limited to areas of relatively abundant rainfall during the growing season. In some cases the rain water is impounded and in other cases it is not. Muth of the rice grown in Central and South America and in many countries in Asia is produced under upland conditions. Fairly satisfactory yields may be produced in seasons of uniformly high rainfall but dry seasons may bring about very low yields. In the Philippines and elsewhere in Southeast Asia, much of the rice is grown on terraces in mountain regions. Sometimes the entire
Edited by T.H. Johnston, Research Agronomist and Technical Advisor. Rice
Breeding, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, in cooperation with University of Arkansas Rice Branch Experiment Station, Stuttgart, Arkansas 72160
mountainside has been converted into a series of rice paddies. Spillways permit the impounded water to flow down from one terrace to another.
Floating rice is grown in some areas of southeastern Asia where streams overflow during the growing season. Specially adapted varieties are sown before the flood season. The water rises slowly and the plants elongate rapidly as the depth of the water increases. The rice culms are weak but are supported by the water. When the flood water recedes, the plants lodge but enough upright growth is made to hold the panicles off the ground so grain can be produced. Such rice must be harvested by hand. In recent years rice breeders in Thailand, and perhaps elsewhere, have had some success in developing floating varieties that show reduced straw growth and more resistance to lodging. However, the plants have retained the ability to elongate rapidly when the need arises.
Temperature and Water
Rice needs relatively high temperatures during the entire growing season, and hence is restricted to tropical climates or to warm seasons of subtropical and temperate zones. The water requirement for rice is rather high and lowland rice may be flooded most of the growing season which may extend over a period of 3 to 5 months. The amount of irrigation water required is least where the subsoils are relatively impermeable and the seasonal rainfall is high. Water of good quality is needed for satisfactory rice production.
Considerable variation exists in methods used to provide water for irrigation. The water source may range from natural seasonal flooding of low-lying areas along streams to elaborate systems of dams, impoundments, and canals to provide complete water control. Water may be pumped from wells or may be obtained from streams by means of relift pumps and use of open ditches trend is toward development of well constructed and efficient irrigation facilities that make maximum use of water for year-round crop production where temperatures are suitable, The more primitive systems that depend on natural flooding may produce relatively low yields of rice because of the uncertainty of water supply, and the difficulty of timely execution of cultural practices including weed control and fertilization,
Effective irrigation implies not only an adequately controlled supply of good quality water, but also efficient drainage of excess water whenever this is required. In cases where rice is direct-seeded rather than transplanted, good drainage is needed to allow the land to dry out enough for preparation of a satisfactory seedbed. Sometimes it is necessary to drain a rice field to allow the soil surface to dry and permit aeration of the rice root system in early midseason to prevent damage from straighthead disease. Earlier drainage may be needed to lessen chances for damage from adverse soil conditions or from insects such as the rice water weevil. Flooded rice fields usually are drained 1 or 2 weeks prior to maturity of the rice. This is especially necessary when rice is harvested mechanically or when storms cause the rice plants to lodge or fall over severely, If it is not possible to drain fields adequately at this stage, then it is very important that the rice varieties being grown possess postharvest dormancy; otherwise the grains on culms which have fallen into the water will germinate while still on the panicle.
Lowland (wetland) rice is grown mostly on rather heavy
clay soils or other soils underlain with a hardpan or impervious subsoil. The seepage loss of water through such soils is small and these soils may not be as suitable for other crops which require deeper root systems to produce satisfactory yields.
Upland or rained rice is grown = soils of many types,
in regions of high to moderate rainfall where the soil profile may be wet most of the time or only occasionally, Upland rice therefore is generally far less productive than irrigated rice, especially in low rainfall years.
Soils wbicb are high in sodium, are saline, or are alkaline, usually are not satisfactory for rice production. Rice does best on soils that are slightly acid, If streams or other sources of irrigation water becomes contaminated with sea (salt) water, rice plants may be damaged. Rice can tolerate somewhat higher concentrations of salt as the plants get larger but high concentrations may kill young plants and may cause sterility (lack of seed production) in older plants around flowering time. The degree of damage is partly dependent on soil type and on the variety being grown, Certain varieties possess more tolerance than others to adverse soil and water conditions. It may be possible to grow rice satisfactorily on problem. soils that are somewhat alkaline by applying small amounts of zinc to the soil at the start of the growing season, Also, the application of ammonium sulfate as the source of early season nitrogen fertilizer may greatly benefit young rice plants growing on moderately alkaline soils.
Availability of Improved Varieties
Plants of different rice varieties (cultivars) range in height from about 60 to 180 cm. They may produce from one to many tillers or culms depending on such factors as plant spacing, variety or type, soil fertility level, available moisture, and pest and disease control. Each culm normally bears a terminal panicle that may contain as many as 100 to 150 grains which are enclosed tightly in a pair of hulls (or husks), the lemma and palea. At maturity the panicle characteristically is fully exerted from the sheath of the uppermost leaf (also called the "boot"), but in some cases it may be partly enclosed. Hull color may be light strawyellow, gold, or a shade of red, purple, or brown. After the hulls are removed, the kernels (brown rice) of different varieties range from 3.5 to 8.0 mm in length, 1.7 to 3.0 mm in width, and 1.3 to 2.3 mm in thickness. Rice cultivars grown in the United States are classed as long-, medium-, and short-grain. The average length of brown rice kernels is 6.61 to 7.5 mm for long-grain, 5.51 to 6.6 mm for mediumgrain, and 5.5 mm or less for short-grain types. The average length/width ratios are over 3, 2.1 to 3 and up to 2.1 mm, for long-, medium-, and short-grain types, respectively. Brown rice of certain varieties grown in other countries shows a wider range in kernel measurements.
Most people desire rice of a specific grain type or at
least rice having certain cooking and processing characteristics. Rice varieties differ greatly in quality, including cooking and processing characteristics. The amylose starch content of milled rice is closely associated with cooking quality. For example, the typical long-grain varieties grown in the United States have relatively high amylose content and the milled rice cooks up dry and flaky and kernels remain separated. Typical medium- and ,short-grain varieties have lower amylose content and the kernels tend to stick together when cooked. Glutinous or waxy rice (sometimes called sweet rice) which is grown in some countries for special uses contains virtually no amylose. Several chemical and physical tests are used to accurately determine cooking and processing characteristics of rice varieties. Rice breeders work very closely with cereal chemists in well developed rice research centers to insure that new improved rice varieties have the desired quality characteristics.
The nutritive value of rice is very important and research investigations were started over 20 years ago by Adair and coworkers in Arkansas (U.S.A.) to breed for increased protein content in rice varieties. Research to improve the inherent nutritional value of rice, particularly with respect to protein content and quality, has been continued and expanded in Arkansas and at other locations in the United States, especially at the
USDA Agricultural Research Center at Beltsville, MD. In recent years, considerable emphasis has been placed on improving the nutritional quality of rice varieties at the International Rice Research Institute in the Philippines and other Rice Research Centers. To date, adapted experimental varieties and breeding lines have been developed which consistently average two percentage points (20 to 25%) higher protein content in the brown rice than the standard cultivars. Much research also is being conducted on lysine and other amino acids in the rice protein, including detailed feeding experiments to evaluate the nutritional value of the improved rice varieties.
Great strides have been made by rice breeders in developing improved cultivars with much shorter and stiffer straw. These variety improvement programs are cooperative with other agronomists, soil and fertilizer specialists, pathologists, physiologists, entomologists, and researchers in other related disciplines. This insures development of varieties that: are responsive to nitrogen fertilization; have desirable plant type including a high degree of resistance to lodging; have resistance to production hazards such as diseases, insects, and adverse soil conditions; and that produce relatively high and stable field and milling yields of rice with desirable cooking and processing characteristics.
During the past 15 years (sixties and early seventies), socalled semi-dwarf or short-statured, stiff-strawed, high-yielding varieties (HYV's) that respond to high levels of nitrogen fertilization have been developed in the coordinated breeding programs in Taiwan, Japan, The International Rice Research Institute in the Philippines, India, Thailand, Colombia, the United States, and perhaps elsewhere. The International Rice Research Institute used improved varieties from Taiwan, the Philippines and other Asiatic countries to develop high-yielding varieties and the accompanying "package" of fertilization and cultural practices that sometimes produce as much as 8,000 to 9,000 kg/ha of paddy, in contrast to the average of 2,000 kg/ha for most farming regions of Asia. Certain imp roved varieties developed in the U.S.A. and elsewhere which are somewhat taller than the "short-statured" types, produce equally high grain yields under certain conditions using somewhat lower levels of N-fertilization. However, these HYV's which are of moderate plant height usually are more susceptible to lodging than are the short-statured types.
It is possible that the very rapid increase in acreage of
a single improved variety of a crop such as rice could be undesirable. An important danger arises when a large geographic area is planted to one specific variety. If an epidemic of a certain disease occurs to which that variety is highly susceptible, then
damage from that disease may be devastating over much of that area. If, however, the large planted areas are divided among three or four different varieties of different genetic background and which have varying responses to major diseases or insects, losses to such epidemics should be much less severe.
In order to get maximum grain production, it has been
found necessary not only to adopt the improved high-yielding varieties but also to employ the appropriate season of planting, the necessary density of plants per hectare, adequate fertilization and pest control, and prompt harvesting. Planting high-yielding cultivars without using improved cultural practices may be relatively useless.
In any given country or geographic area, it is important
to grow only those varieties that are well-adapted to the area. Where possible, it also is important to growvarieties that have the proper grain type and cooking characteristics desired by the consumers.
Cultural Practices (Lowland Rice)
Where and when it is economically feasible, it is desirable to rotate rice with other crops that are adapted to the area. Common rotations in the United States where rice is directseeded and only one rice crop is grown per year, include: riceoats-soybeans, and sometimes lespedeza which may be overseeded in the oats; rice-soybeans-soybeans; 2 years rice- 3 yearsimproved pasture, or other combinations of rice and pasture, either improved or unimproved. Pastures for grazing cattle are improved by seeding clovers or grasses into the rice stubble following combine harvesting and applying fertilizer to the pastures as needed.
In most rice-producing areas of the United States, crops
are rotated because under continuous cropping the soil usually becomes depleted in fertility and in organic matter. The resulting deterioration of the physical condition of the soil makes preparation of a suitable seedbed very difficult. In addition, the soil becomes progressively infested with weeds and diseases that lower the yield and the quality of the rice.
At the International Rice Research Institute in the Philippines, Bradfield conducted intensive rotation experiments with transplanted rice. He alternated crops of rice with soybeans or grain sorghums and by using short-season varieties, was able
to produce four crops that included two high-yielding crops of rice and two other crops in only slightly more than a 12month period. Rotations that may prove satisfactory in other countries may include other crops such as wheat, maize, food legumes, groundnuts, and vegetables.
When it is necessary to grow rice on land continously, it
is very important to follow all possible measures for controlling. wqeeds, diseases and insects. Working all remaining rice stubble or we-ed growth into the so-il or mud following harvest so -it will decay usually helps to control these pests.
In countries where large fields are used and rice is
direct-seeded for mechanized production, proper seedbed preparation is very important. Good drainage is necessary so that dryland equipment such as plows or disk-plows of various types can be used to at least partially turn under crop residues or incorporate them into the soil immediately after harvest. After the field has been left for 2 or 3 months during cold weather to allow time for the crop residues to decay, the land is again worked with disk-harrows, spring-tooth harrows, field cultivators or other similar implements to break up any clods and destroy any vegetation present. Then the field is worked with land-levellers or land-planes to fill in any low places. The soil surface is made as level as possible to provide good drainage and to aid in careful control of water depth when the field is flooded. A uniform but shallow depth of flood water (5 to 10 cm) is desirable for best results with improved shortstatured varieties.
Where the crop is to be transplanted from seedling beds,
a well-prepared field or paddy should have the following characteristics: (1) mud and water should be thoroughly mixed, (2) weeds, rice straw and stubble or other crop residues which were plowed under should be thoroughly decayed, and (3) land should be well levelled and puddled. Careful levelling is important for uniform distribution of irrigation water in the paddy. (Detailed instructions for production of rice seedlings are given in a booklet dated 1972 by The International Rice Research Institute, P.O. Box 583, Manila, Philippines, entitled "Tropical Rice Growers Handbook - Production of Seedlings." General recommendations for growing transplanted rice are presented in a "Rice Production Manual" compiled by Rice Information Cooperative Effort - R.I.C.E. - Univ. of the Philippines College of Agriculture in cooperation with I.R.R.I.). The rice fields should be kept wet and can be worked with recently developed small tractors and specially developed equipment or with the more traditional equipment and animal power.
Seed and Seeding or Planting
Care should be taken to use the best seed available of varieties that are well adapted to the area where the crop is to be grown. Important factors are genetic purity of the variety, freedom from mixtures of other varieties and weeds, and seed with low moisture content and high germination. These items should be considered both for direct seeding and for seedbed production of seedlings to be transplanted. Methods of growing the seedlings include: (1) ordinary wet-bed where seeds are sown on raised beds with drainage ditches between if soil is fertile, nitrogen fertilization may not be needed where needed, nitrogen is worked into the soil prior to seeding;
(2) dry-bed method where water is limited and.raised beds are prepared dry with canals between beds -- pre-germinated seed is sown evenly over the bed and covered with fine salid; (3) "Dapog" method (used extensively in southern Luzon, Philippines) may be used where water is abundant -- the surface of the slightly raised seedbeds.is covered with banana leavesempty cement or fertilizer bags, sheets of plastic, or small concrete slabs -pre-germinated seed is sown thickly and water is splashed on the developing seedlings twice a day for 3 or 4 days - then the seedlings are flooded to a depth of 1 to 2 cm for 10 to 14 days after whi6h they are ready for transplanting in small clumps. If the "dapog" method is used, often 5 to 10 seedlings may be planted per hill but with other methods and older seedings, 2 to 4 seedlings per hill are sufficient.
Fields for transplanting should be cultivated thoroughly
and carry a shallow flood so the seedlings can easily be thrust into the soft mud, Hills of seedlings may be spaced 20 x 25 cm, Closer spacing is desirable where improved cultural practices are being used. Satisfactory field preparation for transplanted rice usually involves an initial flooding to soften the soil, and repeated cultivation (by hand, animal-draw, or power-driven equipment) to incorporate all vegetation and preplant fertilizers. Perennial weeds are thus destroyed and insect pests are greatly reduced in numbers by the thorough soil preparation.
Rice may be direct-seeded with mechanical drills which distribute the seeds uniformly in shallow rows that are covered with soil as part of the seeding operation. Often a heavy metal roller is used to make the seedbed more firm and to help conserve moisture. Other methods include broadcast-seeding of dry seed by airplanes, by hand, or by special ground equipment on a prepared seedbed that is dry or a prepared seedbed that has recently been flooded to a depth of about 10 cm. Where seed is to be broadcast into the water, the seed may be pregerminated for 24 to 36 hours immediately prior to seeding by airplane or other means. When appropriate materials and methods
are available it is advisable to treat the seed with a recommended fungicide to help insure better stand establishment.
Where rice is to be direct-seeded, it is necessary to choose a suitable variety,,and an ample supply of irrigation water must be readily available. -Suitable and effective means also must be available for controlling weeds and insect pests. Suggested seeding rates for low-tillering varieties range from 90 to 120 kg/ha of seed where rows are spaced 15 to 25 cm apart; for high-tillering varieties, a 60 to 80 kg/ha rate should be adequate. If the germination percentage of the seed is less than 80%, then the seeding rate should be increased proportionately to produce An adequate stand of plants. Research in Arkansas (cooperative U.S. Dept. of Agr. and Arkansas Agr. Exp. Sta.) showed that 150 to 300 rice seedlings per square meter was a desired stand. However, 50 plants of barnyardgrass per square meter competing throughout the growing season, reduced grain yields by nearly 50%. Fairly satisfactory grain yields may be obtained with somewhat fewer plants if weeds are controlled and ample and timely nitrogen fertilizer applications are made.
Proper balance of the major fertilizer elements (potassium, phosphorus, and nitrogen) is necessary for top production by the new, so-called, high-yielding, rice varieties. These improved varieties, especially the short-statured, stiff-strawed or non-lodging types, usually respond well to rather high levels of available nitrogen. Newly cleared woodland may be high in native nitrogen but most of this nitrogen is utilized by the first two or three rice crops. It then is necessary to provide the needed nitrogen through green manure crops, which are turned under into the soil, or by application of commerical fertilizers. Ammonium sulfate and urea are the most satisfactory commercial nitrogenous fertilizers for application early in the growing season. Anhydrous ammonia is fairly satisfactory for preplant applications in lowland rice production if it is applied to a sufficient depth (10 to 15 cm) and sealed in the soil so it does not escape to the atmosphere. Other forms of N-fertilizer such as ammonium nitrate and liquid solutions of N may be satisfactory sources for midseason applications. Plants of responsive rice varieties require moderately high levels of N early in the growth cycle for establishment of a good root system and for tillering. The other peak period of need for N is early in the reproductive stage of growth when the panicle starts to develop and beg ins to form the grain. If N-fertilizer is applied late in the vegetative growth stage, excessive stem growth and elongation usually follows and severe early lodging may result. Delaying midseason N application until after stem
elongation has started, usually results in less straw growth and reduces chances for severe lodging. Under lowland rice production, proper water management is very important to prevent loss of nitrogen from the soil.
Only relatively low levels of N-fertilization can be tolerated by local or indigenous varieties which generally lodge badly with even moderate levels of N. In contrast, relatively high rates of N-fertilizer are necessary to boost the yields of improved, short-statured, responsive varieties up to 7 to 8 metric tons (7,000 to 8,000 kilos) of grain per hectare. However, many of these improved varieties will produce as much grain as local varieties when low levels of Nfertilizer are used on both.
When high total rates (above 100 kg/ha of actual N) of N-fertilizer are used on the HYV's, it usually is advisable to divide the total amount into three applications. Applying 40 to 50% of the total N early in the season and the remainder in two equal increments at midseason helps prevent excessive vegetative growth which tends to make rice plants more susceptible to several diseases. Research in Arkansas (U.S.A.) showed normally grows to a moderate plant height (115 to 125 cm), proper timing of the midseason N-fertilization reduced plant height by 18 cm, reduced lodging from 69%~ to only 2%, and increased grain yield from 5,700 to 7,900 kg/ha. For best results from rather high rates of total N, the first midseason application should be made when the first elongating internode of 50% of the main stems of a given variety reaches a specified length. For the popular, stiff-strawed, Starbonnet variety this length is about 12 mm whereas for other varieties with somewhat less lodging resistance, the specified length is about 37 mm. This usually corresponds to the time when the developing panicle is about 2 mm long. A few main stems are split open with a knife to determine stage of plant development. The second midseason increment of N-fertilizer should be applied about 10 days after the first midseason application. On large, direct-seeded fields, these midseason applications are made from airplanes without draining the irrigation water from the fields.
Part, if not all, of the phosphate and potash needs of lowland rice may be provided by the incorporation of animal dung, composts, green manures, and crop residues of previous crops that are incorporated into the soil during seedbed preparation. Where available and needed, applications of commercial potash and phosphate fertilizers may be worked into the soil prior to seeding or transplanting.
Control of weeds, diseases, and insect pests of rice are necessary to reach satisfactory levels of production in any type of rice culture. Planting rice in rows facilitates the use of small weeding devices and hand applications of chemicals to control important pests. All types o,'f rice pests tend to be more abundant on land cropped continuo*3'ly to rice but their abundance can be reduced substantially when rice is rotated- with other crops, e-speci-ally- row-crops,-in which weeds and other pests are controlled. Weeds compete with rice plants for nutrients, sunlight, and moisture and should be removed or controlled early in the growing season to avoid severe yield reductions. Disease organisms, rodents, and insects may live and multiply in crop residues or weeds and trash at the edges of fields. Clean cultivation will help to keep harmful insect and rodent populations to a minimum. The growing of varieties that are resistant to specific diseases and insects helps to reduce the abundance of these pest organisms. Rodents and birds sometimes damage the rice crop severely and they should be controlled insofar as possible.
Insects which can prove very harmful to rice producti-on in various parts of the world include the gall midge, several species of stem borer, the green leaf hopper and brown plant hopper which are vectors or carriers of virus diseases, the rice water weevil, and the rice stinkbug. Partial to sometimes almost complete control of some of these pests may be provided by using good agronomic practices, timely applications of suitable insecticides, and growing resistant varieties, when available,
Diseases which can be very damaging include blast, which
may be especially severe in upland rice, tungro virus and other viruses which may be very severe in'some rice-growing countries, bacterial leaf blight, and several-other seedling, foliar and stem diseases. Effective control of these diseases depends on the use of good agronomic practices, including timely but not excessive applications of N-fertilizer, breeding for resistance as new varieties are developed, and, in some cases, chemical applications to control the disease organism or the insect vector,
Weeds in rice fields may best be controlled by a combination of practices including thorough preparation of the soil-prior to seeding or transplanting the rice, timely application of suitable chemicals, clean cultivation of rice growing in rows, and hand weeding. Control of weeds in other crops grown in rotation with rice also is very important. The use of herbicides for
weed control has greatly increased in recent years. However, it is very important to use suitable rates and timing of specific herbicides that will kill the weed species present without severely or permanently damaging the rice crop or adjacent fields of other crops. A very recent development in methods of controllingspecific weed species is the control of northern jointvetch (curly indigo) in rice fields by spraying millions of artificially propagated spores of the organism which causes an anthracnose disease on the weed, The method was developed by Smith and co-workers in Arkansas (cooperative research, U.S. Dept. Agr. and Arkansas Agr. Exp. Sta.). The disease organism has not affected numerous other weed and crop species tested to date.
Weeds and insect pests and diseases that are serious on rice, vary greatly from region to region. It is highly essential to identify a potential outbreak of important pests as soon as possible,,so that treatments for their control can be used on each pest at its most vulnerable stage.
For further information on Crop Protection, see Chapter
4 in the book -- "Tropical Agriculture" by Wrigley. (Reference list following Chapter 40).
Upland Rice Production
Upland rice is sometimes termed "dry-land paddy", despite the fact that successful non-irrigated rice culture is largely confined to regions where rainfall during the growing season is such that the soil is continuously moist, Rice is a heavy user of water, and upland rice will yield well only with abundant rainfall. Regions having periods of 4 to 6 months with 130 to 180 millimeters of well distributed rainfall each month, have a potential for satisfactory upland rice production, Rice does not tolerate dessication, especially during flowering, at which time the panicles are emerging from the boot or sheath of the flag leaf (uppermost leaf) and pollination of the florets are taking place.
Soil type is an important factor in upland rice production since it affects the soil's moisture holding power. Deep soils that permit extensive root growth and have the texture and structure to receive and hold substantial amounts of rainfall, usually are most productive. Rice has an advantage over other upland cereal grains in being more tolerant of acid soils and less sensitive to occasional water-logging.
Upland rice is suited for crop rotation systems which include other staple crops such as an oilseed crop, cassava, taro, maize, sorghum, and legumes. The alternate crops are grown in seasons of lesser rainfall. Upland rice is classed