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Original:Traditional Field Crops 7
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- 1 Traditional Field Crops (Peace Corps, 1981, 283 p.)
- 1.1 An introduction to the reference crops
Traditional Field Crops (Peace Corps, 1981, 283 p.)
An introduction to the reference crops
There are several reasons why the six reference crops -maize, grain sorghum, millet, peanuts, field beans, and cowpeas -are grouped together in one manual. All of the reference crops are row crops (grown in rows) and because of this, they share a number of similar production practices. Also, in developing nations, two or more of the crops are likely to be common to any farming region and are frequently interrelated in terms of crop rotation and intercropping (see Chapter 4, page 91) In addition, all of them are staple food crops. The developing countries are major producers of the reference crops, with the exception of maize.
Cereal crops versus pulse crops
Maize, grain sorghum, and millet are known as cereal crops, along with rice, wheat, barley, oats, and rye. Their mature, dry kernels (seeds) are often called cereal grains. All cereal crops belong to the grass family (Gramineae) which accounts for the major portion of the monocot (Monocotyledonae) division of flowering (seed-producing) plants. All monocot plants first emerge from the soil with one initial leaf called a seed leaf or cotyledon.
A germinating maize seedling; note that it has only one seed leaf, which makes it a monocot. Monocots emerge through the soil with a spike-like tip. They generally have fewer problems with clods and soil dusting than dicots.
Peanuts, beans, and cowpeas are known as pulse crops, grain legumes or pulses, along with others such as lima beans, soybeans, chickpeas, pigeonpeas, mung beans, and peas. The pulses belong to the legume family (Leguminosae) whose plants produce their seeds in pods. Some legumes like peanuts and soybeans are also called oilseeds because of their high vegetable oil content.
Germinating maize seed
Table 2 World and Regional Production of the Reference Crops (1977 FAO data)
Total World Production (millions of metric tons)
Percent of World Production Developing Countries
FIELD BEANS, COWPEAS
A germinating bean plant; note the two thick cotyledons (seed leaves) which originally formed the two halves of the seed.
Geminating bean seed
The pulses belong to the other major division of flowering plants called dicots (Dicotyledonae). Unlike the monocots, dicot plants first emerge from the soil with two seed leaves.
In addition, the pulses have two outstanding characteristics for farmers and for those who consume them:
Â· They contain two to three times more protein than cereal grains (see Table 3)
Â· Legumes obtain nitrogen for their own needs through a symbiotic (mutually beneficial) relationship with various species of Rhizobia bacteria that form nodules on the plants' roots (see illustration on page 38).
Nitrogen is the plant nutrient needed in the greatest quantity and is also the most costly when purchased as chemical fertilizer. The Rhizobia live on small amounts of sugars produced by the legume and, in return, convert atmospheric nitrogen (ordinarily unavailable to plants) into a usable form. This very beneficial process is called nitrogen fixation. In contrast, cereal grains and other non-legumes are totally dependent on nitrogen supplied by the soil or from fertilizer.
Nitrogen-fixing nodules on the roots of a bean plant. Note that they are attached to the roots rather than an actual part of them.
Nitrogen fixing nodules
Despite the urgent need to increase both cereal and pulse production in the developing countries, most crop improvement efforts of the "Green Revolution" emphasized the cereals (see page 294). As a result, pulse yields in the region have shown little, if any, increase. In some areas, total pulse production has actually declined in favor of the cereal grains, even though many developing nations suffer from a chronic protein shortage. Fortunately, this situation is now being reversed.
The nutritional value of the reference crops
The cereal grains, with their high starch content and lower prices, make up a major source of energy (calories) in developing countries. There, cereal consumption is high enough to contribute a substantial amount of protein to the diets of older children and adults (although still well below quantity and quality requirements). Another plus is that cereal grains contain a number of vitamins and minerals, including Vitamin A which can be found in the yellow varieties of maize and sorghum. gained from eating large quantities of the cereals, their protein content is relatively low (7-14 percent) and they are deficient in several amino acids. Infants and children, who have much higher protein needs per unit of body weight and smaller stomachs, do not get as much protein from cereals as adults. Studies have also shown that some reference crops lose vitamins and protein in substantial amounts with traditional preparation methods (milling, soaking, and drying).
The pulses have considerably higher protein contents than the cereal grains (17-30 percent in the reference pulses) and generally higher amounts of B vitamins and minerals. Unfortunately they also may have some deficiencies in amino acids.
All animal proteins (meat, poultry, fish, eggs, milk and cheese) are complete proteins (contain all essential amino acids), but their high cost puts them out of reach of much of the population in developing nations.
Fortunately, it is possible to satisfy human protein requirements without relying solely on animal protein sources. The cereals and pulses, though not complete proteins in themselves, can balance out each other's amino acid deficiencies. Cereals are generally low in the essential amino acid lysine, but relatively high in another, methionine. The opposite is true for most of the pulses. If eaten together or within a short time of each other and in the right proportion (usually about a 1:2 ratio of pulse to cereal), combinations like maize and beans or sorghum and chickpeas are complete proteins. In most developing countries, however, pulses are more expensive than the cereal grains, which creates difficulties in achieving a balanced diet.
Table 3 Nutritional Value of the Reference Crops (dry weight basis)
An introduction to the individual crops
Maize (Zea mays)
Distribution and Importance
In terms of total world production, maize and rice vie for the number two position after wheat. Several factors account for the importance of maize:
Â· Maize can adapt to a wide range of temperature, soils and moisture levels and resists disease and insects.
Â· It has a high yield potential.
Â· It is used for both human and animal consumption.
Types of Maize
There are five principal types of maize:
Â· Dent: The most widely grown type in the U.S. The seed has a cap of soft starch that shrinks and forms a dent at the top of the kernel.
Â· Flint: Widely grown in Latin America, Asia, Africa and Europe. The kernels are hard and smooth with very little soft starch. It is more resistant to storage insects like weevils than dent or floury maize.
Â· Floury: Mainly soft starch and widely grown in the Andean region of South America. It is more prone to storage insects and breakage than harder types.
An ear of maize. Each silk leads to an ovula (potential kernel) on the cob. Varieties vary in length and tightness of husk covering, which determines resistance to insects and moisture-induced molds which may attack the ear in the field.
Maize tassel, ear of maize
Parts of young maize plants
Â· Pop: Really an extreme form of flint maize.
Â· Sweet: At least twice as high in sugar as ordinary maize and meant to be consumed in immature form when only about one-third the potential grain yield has been accumulated. It is more prone to field insect damage, especially on the ears.
A potentially very valuable type called hi-lysine maize with more than double the content of lysine is nearing the mass application stage, but still has some field and storage problems to overcome (see the section on maize improvement at the end of this chapter).
Average yield of shelled grain (14 percent moisture) under varying conditions are shown below.
Average Yield of Shelled Grain
Top farmers in the U.S. Corn Belt
Average for developed countries
Average for LDC's
Feasible yield for small scale LDC farmers with improved practices
Source: FAO and USDA data, 1977.
Climatic Requirements of Maize
Rainfall: Nonirrigated (rainfed) maize requires a minimum of around 500 mm of rainfall for satisfactory yields. Ideally, the bulk of this should fall during the actual growing season, although deep loamy or clayey soils can store up to 250 mm of pre-season rainfall in the future crop's root zone. Any of the following factors will act to increase the moisture needs of maize (and other crops):
Â· Long growing periods due to cool temperatures.
Â· Shallow and/or sandy soils with low water-holding ability.
Â· Excessive water runoff due to lack of erosion control on sloping land.
Â· Low humidity, especially when combined with wind.
Maize has some ability to resist dry spells but is not nearly as droughttolerant as sorghum and millet.
Temperature: The optimum growth rate of maize increases with temperatures up to about 32-35Â°C if soil moisture is abundant, but decreases slightly with temperatures around 27-30Â°C when soil moisture is adequate. If soil moisture is low, the optimum growth rate temperature drops to 27Â°C or below. At temperatures of 10Â°C or below, maize grows slowly or not at all and is susceptible to frost. However, daytime temperatures in excess of 32Â°C will reduce yields if they occur during pollination.
Yields are also reduced by excessively high nighttime temperatures, since they speed up the plant's respiration rate and the "burning up" of the growth reserves.
Soil requirements: Maize grows well on a wide variety of soils if drainage is good (no waterlogging). It has a deep root system (up to 185 cm) and benefits from deep soils which allow for improved moisture storage in dry spells. The optimum pH for maize is in the 5.5-7.5 range, although some tropical soils produce good yields down to a pH of 5.0 (very acid). The liming and nutrient needs of maize are covered in Chapter 5.
Response to Daylength: The length of growth period of many plants is affected by daylength. This is known as a photosensitive (photoperiodic) response. Most maize varieties are short day plants which means that they will mature earlier if moved to a region with significantly shorter daylengths than they were bred for. In the tropics, there is relatively little variation in daylength during the year or between regions. Because most temperate zone maize varieties are adapted to the longer daylengths of that area's summer, they will flower and mature in too short a period for good yield accumulation if moved to the tropics. Sweet maize seed from the temperate zone may reach little more than knee height in the tropics, and produce disappointingly small ears, although in record time' Likewise, the "giant" novelty maize advertised in some gardening magazines is nothing more than a variety adapted to the very short daylengths of the tropics. When grown in the temperate zone, the much longer daylengths retard maturity and favor vegetative growth. Some maize varieties, however, are day neutral with little response to variations in daylength.
As mentioned earlier, maize's relatively low protein and high starch content makes it more important as an energy (calorie) source. Many people believe that yellow maize has more protein than white maize, but the only nutritional difference between the two is the presence of Vitamin A in the yellow variety (also called carotene).
Unlike production in the developed countries, maize production in developing countries is almost entirely used for human food in the form of meal, flour, tortillas or a thick paste. In humid areas where increased spoilage problems make grain storage more difficult, a significant portion of maize may be consumed much like sweet corn while it is still in the semi-soft, immature stage.
Maize has numerous industrial and food uses in the form of some 500 products and by-products. Various milling and processing methods can produce starch, syrup, animal feed, sugar, vegetable oil, dextrine, breakfast cereals, flour, meal, and acetone. Maize also is used for making alcoholic beverages throughout the world. Maize Stages of Growth Depending on the variety and growing temperatures, maize reaches physiologic maturity (the kernels have ceased accumulating protein and starch) in about 90-130 days after plant emergence when grown in the tropics at elevations of 0-1,000 meters. At higher elevations, it may take up to 200-300 days. Even at the same elevation and temperature, some varieties will mature much earlier than others and are known as early varieties. The main difference between an early (90-day) and a late (130-day) variety is in the length of time from plant emergence to tasseling (the vegetative period). This stage will vary from about 40 to 70 days. The reproductive period (tasseling to maturity) for both types is fairly similar and varies from about 50 to 58 days. The following discussion describes the growth stages and related management factors of a 120day maize variety.
PHASE I: FROM GERMINATION TO TASSELING
Plants will emerge in four to five days under warm, moist conditions but may take up to two weeks or more during cool or very dry weather. Little if any germination or growth occurs at soil temperatures below 13Â°C. Harmful soil fungi and insects are still active in cool soils and can cause heavy damage before the seedlings can become established. Fungicide seed treatments (see Chapter 6) are usually most beneficial under cool, wet conditions and may increase yields from 10 to 20 percent.
Maize seeds are large and contain enough food reserves to sustain growth for the first week or so after emergence. Then the plants must rely on nutrients supplied by the soil or fertilizer. Up until kneehigh stage, the three major nutrients -nitrogen, phosphorus, and potassium - are required in relatively small amounts, but young seedlings do need a high concentration of phosphorus near their roots to stimulate root development.
The primary roots reach full development about two weeks after seedling emergence and are then replaced by the permanent roots (called nodal roots) which begin growing from the crown (the underground base of the plant between the stem and the roots). Planting depth determines the depth at which the primary roots form but has no effect on the depth at which the permanent roots begin to develop.
Until the plants are knee high, the growing point (a small cluster of cells from which the leaves, tassel, and ear originate) is still below the soil surface, encased by a sheath of unfurled leaves. A light frost or hail may kill the above-ground portion of the plant, but usually the growing point (if below ground) will escape injury, and the plant will recover almost completely. However, flooding at this stage is more damaging than later on when the growing point has been carried above ground by the stalk.
The growing point plays a vegetative role by producing new leaves (about one every two days) until the plants are knee high; then a major change occurs. Within a few days, the underground growing point is carried above ground by a lengthening of the stalk and switches from leaf production to tassel initiation within the plant. (Slit a plant lengthwise at this stage, and you can easily see the growing point as a peaked tip inside the stalk). At this time roots from adjacent rows have reached and crossed each other in the between-row spaces (for rows up to one meter wide).
From tassel initiation until tassel emergence takes about five to six weeks and is a period of very rapid growth in plant height, leaf size, and root development. Maximum root depth can reach 180 cm. under optimum soil, moisture, and fertility conditions and is attained by the time of tassel emergence.
Maximum nutrient uptake occurs from about three weeks before to three weeks after tasseling and maximum water use from tasseling through the softdough stage (about three weeks after tasseling).
PHASE II: TASSELING AND POLLINATION
Tasseling occurs about 40-70 days after plant emergence in 90-130 day varieties. The tassel (flower) is thrust out of the leaf whorl about one to two days before it begins shedding pollen. Pollen shed starts two to three days before the i silks emerge from the ear tip and continues for five to eight days. If conditions are favorable, all the silks emerge within three to five days and most are pollinated the first day.
Each silk leads to an ovule (a potential kernel). When a pollen grain lands on a silk, it puts out a pollen tube that grows down the silk's center and fertilizes the ovule at the other end in a matter of hours. Shortage of pollen is rarely a problem since about 20,00050,000 pollen grains are produced per silk. Poor ear fill (the number of kernels on an ear) or skipped kernels are nearly always caused by delayed silk emergence or by ovule abortion, both of which are caused by drought, overcrowding or a shortage of nitrogen and phosphorus. Extreme heat (above 35Â°C) can diminish pollen vigor and also affect ear fill. Some insects like the corn rootworm beetle (Diabrotica spp.) or Japanese beetle (Popillia japonica) can cut off the silks before pollination.
Maize is cross-pollinated, and usually 95 percent or more of the kernels of a cob receive their pollen from neighboring maize plants. This also means that different maize types such as the hi-lysine varieties must be kept isolated from other maize pollen if they are to retain their desired characteristics.
Pollination is a very critical time during which there is a high demand for both water and nutrients. One to two days of wilting during this period can cut yields by as much as 22 percent and six to eight days of wilting can cut yields by 50 percent.
A few days after pollination, the silks begin to wilt and turn brown. Unpollinated silks will remain pale and fresh looking for several weeks but as mentioned above, they can only receive pollen for a week or so after they emerge from the ear tip.
PHASE III: FROM KERNEL DEVELOPMENT TO MATURITY
Most maize ears have 14-20 rows with 40 or more ovules per row and produce about 500-600 actual kernels. Any shortage of water, nutrients, or sunlight during the first few weeks of kernel development usually affects the kernels at the tip of the ear first, making them shrivel or abort. Maize is very prone to moisture stress (water deficiency) at this stage due to a heightened water requirement (up to 10 mm per day under very hot and dry conditions). Wind damage during early kernel development is seldom serious, even though the plants may be knocked almost flat, since they still have the ability to "gooseneck" themselves (curve up) into a nearly vertical position.
Stages of Kernel Development in Maize
Â· Blister stage: About 10 days after pollination when the kernels begin to swell, but contain liquid with very little solid matter.
Â· Roasting ear stage: About 18-21 days after pollination. Though field maize has a much lower sugar content than sweet maize, at this stage it is still sweet. At this stage the kernels have accumulated only about one-third of the total dry matter yield they will have at physiologic maturity. From this time on, any type of stress is more likely to affect kernel size rather than grain fill at the ear tip.
Â· Dough stage: About 24-28 days after pollination.
Â· Approaching maturity: As maturity nears, the lower leaves begin to turn yellow and die. In a healthy, well nourished plant, this should not occur until the ear is nearly mature. However, any serious stress factordrought, low soil fertility, excessive heat, diseases--can cause serious premature leaf death. Ideally, most of the leaves should still be green when the husks begin to ripen and turn brown. Early death of the maize plant can greatly reduce yields and result in small, shrunken kernels.
Â· Physiologic maturity: About 52-58 days after 75 percent of the field's ear silks have emerged. The kernels have reached their maximum yield and have ceased accumulating more dry matter. However, they still contain about 3035 percent moisture which is too wet for damage-free combine harvesting (picking and shelling) or for spoilage-free storage (except in the form of husked ears in a narrow crib; see Chapter 7). Small farmers usually let the maize stand in the field unharvested for several weeks or more to allow some further drying. In some areas, particularly Latin America, it is a common practice to bend the ears (or the plants and the ears) downward to prevent rain from entering through the ear tips and causing spoilage. It also helps minimize bird damage and lets in sunlight for any intercropped plants that may be seeded at this time.
Number of ears per plant: Most tropical and sub-tropical maize varieties commonly produce two to three useful ears per plant under good conditions. In contrast, most U.S. corn belt types are single eared. One advantage of multipleeared varieties (often called prolifics) is that they have some built in buffering capacity in case of adverse conditions and may still be able to produce at least one ear.
Grain Sorghum (Sorghum bicolor)
Distribution and Importance Although grain sorghum accounted for only 3.6 percent of total world cereal production in 1977 (FAO data), several factors make it an especially important crop in the developing world:
Â· The developing nations account for about 60 percent of the world's grain sorghum production.
Â· It is drought-resistant and heat-tolerant and particularly suited to the marginal rainfall areas of the semiarid tropics (such as the savanna and Sahel zones of Africa where food shortages have been critical).
Types of Sorghums
Grain Sorghum vs. Forage Sorghum: Where sorghum is grown in the developed world, a definite distinction is made between forage so_ghum and grain sorghum types. For example, in the U.S. (where grain sorghum is often called "milo"), nearly all grain types have had dwarf genes bred into them to reduce plant height to 90-150 cm for more managable machine harvesting, In contrast, forage sorghum types are much taller and have smaller seeds and a higher ratio of stalk and leaves to grain. They are used largely for cattle feed as fresh green chopped forage or silage (green forage preserved by a fermentation process), but are sometimes grazed. Sudangrass is a variety of forage sorghum with especially small seedheads and thinbladed leaves, and sorghumsudan crosses also are available.
A grain sorghum plant nearing maturity
In the developing countries, especially where cattle are important, most traditional grain sorghum varieties have some forage type characteristics such as tallness and a high proportion of stalk to leaves.
There are many regional variations among local grain sorghum types:
Yields of Dry Grain
Top yields in the U.S. under irrigation
Top rainfed yields in the U.S.
Average for the developed countries
Average for developing countries
Feasible rainfed yields for farmers using improved practices
Sweet Sorghum (Sorgo) and Broomcorn: Sorgo types have tall, juicy stalks with a high sugar content and are used for making syrup and also for animal feed in the form of silage and forage. Broomcorn is a sorghum type grown for its brush, which is used mainly for brooms.
Grain sorghum exhibits greater yield stability over a wider range of cropping conditions than maize. Although it will outyield maize during below-normal rainfall periods, the crop might suffer some damage under very high rainfall. Yields of dry (14 percent moisture) grain are shown under varying growing conditions on page 52 (based on FAO, USDA, and international research institute data).
Protein content vs. yield: The protein content of sorghum kernels can vary considerably (7-13 percent on soils low in nitrogen) due to rainfall differences. Since nitrogen (N) is an important constituent of protein, kernel protein content is likely to be highest under very low rainfall that cuts back yields and concentrates the limited amount of N in a smaller amount of grain. Protein fluctuation is much less on soils with adequate nitrogen.
Climatic Requirements of Sorghum
Grain sorghum tolerates a wide range of climatic and soil conditions.
Rainfall: The sorghum plant, aside from being more heat- and drought-resistant than maize, also withstands periodic waterlogging without too much damage.
The most extensive areas of grain sorghum cultivation are found where annual rainfall is about 4501,000 mm, although these higher rainfall areas favor the development of fungal seed head molds that attack the exposed sorghum kernels. The more open-headed grain sorghum varieties are less susceptible to head mold.
Several factors account for the relatively good drought tolerance of grain sorghum:
Â· Under drought conditions the plants become dormant and will curl up their leaves to reduce water losses due to transpiration (the loss of water through the leaf pores into the air).
Â· The leaves have a waxy coating that further helps to reduce transpiration.
Â· The plants have a low water requirement per unit of dry weight produced and have a very extensive root system.
Temperature and Soil Requirements: Although sorghum withstands high temperatures well, there are varieties grown at high elevations that have a good tolerance to cool weather as well. Light frosts may kill the above-ground portion of any sorghum variety, but the plants have the ability to sprout (ratoon) from the crown.
Sorghum tends to tolerate very acid soils (down to pH 5.0 or slightly below) better than maize, yet it is also more resistant to salinity (usually confined to soils with pH's over 8.0).
Response to Daylength (Photosensitivity)
Most traditional sorghum varieties in the developing countries are very photosensitive. In these photosensitive types, flowering is stimulated by a certain critical minimal daylength and will not occur until this has been reached, usually at or near the end of the rainy season. This delayed flowering enables the kernels to develop and mature during drier weather while relying on stored soil moisture. (This is actually a survival feature which allows seed heads to escape fungal growth in humid' rainy conditions.) These local photosensitive varieties usually will not yield as well outside their home areas (especially further north or south) since their heading dates still remain correlated to the rainy season and daylength patterns of their original environment. Despite this apparent adaptation to their own areas, the traditional photosensitive varieties have a relatively low yield potential and may occupy land for a longer period to produce a good yield (due to their fixed flowering dates). In addition there is always the danger that the rains will end early and leave an inadequate reserve of soil moisture for kernel development. Breeding programs are attempting to improve these photosensitive types, and many of the improved varieties show little sensitivity to daylength. Other Sorghum Characteristics Ratooning and Tillering Ability
The sorghum plant is a perennial (capable of living more than two years). Most forage sorghums and many grain varieties can produce several cuttings of forage or grain from one planting if not killed by heavy frost or extended dry weather. New stalks sprout from the crown (this is called ratooning) after a harvest.
*DANGER* The Toxicity Factor: Hydrocyanic Acid
Young sorghum plants or drought-stunted ones under 60 cm tall contain toxic amounts of hydrocyanic acid (HCN or prussic acid). If cattle, sheep or goats are fed on such plants, fatal poisoning may result. Fresh, green forage, silage, and fodder (dried stalks and leaves) are usually safe if over 90-120 cm tall and if growth has not been interrupted. The HCN content of sorghum plants decreases as they grow older and is never a problem with the mature seed. An intravenous injection of 2-3 grams of sodium nitrite in water, followed by 4-6 grams of sodium thiosulfate is the antidote for HCN poisoning in cattle; these dosages are reduced by half for sheep.
However, ratooning ability has little value in most areas where non-irrigated sorghum is grown. In these areas, either the rainy season or frost-free period is likely to be too short for more than one grain crop or too wet for a mid-rainy season first crop harvest without head mold problems. However, forage sorghums take good advantage of ratooning, since they are harvested well before maturity, usually at the early heading stage. Cattle farmers in El Salvador take three cuttings of forage sorghum for silage-making during the six-month wet season. In irrigated tropical zones with a year-round growing season such as Hawaii, it is possible to harvest three grain crops a year from one sorghum planting by using varieties with good ratooning ability.
Some grain sorghum varieties have the ability to produce side shoots that grow grain heads at about the same time as the main stalk (this is called tillering). This enables such varieties to at least partially make up for too thin a stand of plants by producing extra grain heads.
Nutritional Value and Uses of Sorghum
Nearly all grain sorghum used in the developed world is fed to livestock (mainly poultry and swine). However, in developing countries it is an important staple food grain and is served boiled or steamed in the form of gruel, porridge, or bread. In many areas, it is also used to make a home-brewed beer. In addition, the stalks and leaves are often fed to livestock and used as fuel and fencing or building material.
Like the other cereals, grain sorghum is relatively low in protein (8-13 percent) and is more important as an energy source. If eaten along with pulses in the proper amount (usually a 1:2 grain:pulse ratio), it will provide adequate protein quantity and quality. Only those varieties with a yellow endosperm (the starchy main portion of the kernel surrounding the germ) contain vitamin A.
Because sorghum is very susceptible to bird damage during kernel development and maturity, birdresistant varieties have been developed. Because it has a high tannin content in the seeds, stalks, and leaves, it is partly effective in repelling birds from the maturing seedheads. However, these high tannin varieties are more deficient in the essential amino acid lysine than ordinary varieties which has consequences for humans and other monogastrics like pigs and chickens. In the U.S., this is overcome by adding sythetic lysine to poultry and swine rations that are made from birdresistant sorghum grains. In developing countries a slight increase in pulse intake can overcome this problem in humans.
Grain Sorghum Growth Stages
Depending on variety and growing temperatures, nonphotosensitive grain sorghum reaches physiologic maturity in 90-130 days within the 0-1000 m zone in the tropics. However, the local, daylength-sensitive varieties may take up to 200 days or more because of delayed flowering. At very high elevations, all varieties may take 200 days or more.
As with maize, the main difference between a 90-day and 130day sorghum variety is in length of vegetative period (the period from seedling emergence to flowering). The grain filling period (pollination to maturity) is about the same for both (30-50 days). The following sections describe the growth stages and management factors of a typical 95-day variety. These principles remain the same no matter what variety is grown.
PHASE I: FROM EMERGENCE TO THREE WEEKS
Sorghum seedlings will emerge in three to six days in warm, moist soil. Under cool conditions where emergence is delayed, the seeds are especially prone to harmful soil fungi and insects, and a fungicide/ insecticide seed dressing may be particularly beneficial (see Chapter 6). Compared to maize, the small sorghum seeds are low in food reserves which are quickly exhausted before enough leaf area is developed for photosynthesis. For this reason the seedlings get off to a slow start during the first three weeks, after which the growth rate speeds up.
This sluggish beginning makes good weed control extra important during this time.
For the first 30 days or so, the growing point which produces the leaves and seedhead is below the soil surface. Hail or light frost is unlikely to kill the plant, since new growth can be regenerated by the growing point. However, regrowth at this stage is not as rapid as with maize.
PHASE II FROM THREE WEEKS TO HALF-BLOOM
(60 days after emergence)
Growth rate and the intake of nutrients and water accelerates rapidly after the first three weeks. The "flag" leaf (the final leaf produced) becomes visible in the leaf whorl about 40 days after emergence. "Boot" stage is reached at about 50 days when the flower head begins to emerge from the leaf whorl but is still encasea by the flag leaf's sheath. The head's potential size in terms of seed number has by now been determined. Severe moisture shortage at boot stage can prevent the head from emerging completely from the flag leaf sheath. This will prevent complete pollination at flowering time.
Half-bloom stage is reached at about 60 days when about half of the plants in a field are in some phase of flowering at their heads. However, an individual sorghum plant flowers from the tip of the head downward over four to nine days, so half-bloom on a per plant basis occurs when flowering has proceeded halfway down the head. Although time to half-bloom varies with variety and climate, it usually encompasses two-thirds of the period from seedling emergence to physiologic maturity. In keeping with the rapid rates of growth and nutrient intake, about 70, 60, and 80 percent of the nitrogen, phosphorus, and potassium requirements (respectively) have been absorbed by the plant by the time of half-bloom. Severe moisture shortage at pollination greatly cuts yields by causing seed ovule abortion and incomplete pollination.
PHASE III: FROM HALF-BLOOM TO PHYSIOLOGIC MATURITY (60-95 days)
The seeds reach the soft dough stage about 10 days after pollination (70 days after emergence) in a 95-day variety, and about half of the final dry weight yield is accumulated during this short period. Hard dough stage is reached in another 15 days (85 days after emergence) when about threefourths of the final dry weight grain yield has been attained. Severe moisture stress during this period will produce light, undersized grain. Physiologic maturity is reached in another 10 days (95 days from emergence in the case of this variety.) At this stage, the grain still contains 25-30 percent moisture which is well above the 13-14 percent safe limit for storage in threshed form (after the seeds have been removed from the head). Small scale farmers can cut the heads at this stage and dry them in the sun before threshing or let the heads dry naturally on the plants in the field.
TYPES OF MILLET
The millets comprise a group of small-seeded annual grasses grown for grain and forage. Although of little importance in the developed world, they are the main staple food grain crop in some regions of Africa and Asia and are associated with semi-arid conditions, high temperatures, and sandy soils. Of the six major millet types listed below, pearl millet is the most widely grown and will receive the most emphasis in this manual.
Millets - How a sorghum plant develops
Other Names: Bulrush, cattail, and spiked millet, bajra, millet, milt
Scientific Name: Pennisetum typhoides, P. glaucum or P. americanum
Main Areas of Production: Semi-arid plains of southern Asia (especially India) and the Sahel (sub-Saharan) region of Africa.
Important Characteristics: The most drought- and heat-tolerant of the millets; more prone to bird damage than finger millet.
Other Names: Birdsfoot millet, eleusine, ragi
Scientific Name: Eleusine coracana
Main Areas of Production: The southern Sudan, northern Uganda, southern India, the foothills of Malaysia and Sri Lanka
Important Characteristics: Unlike other millets, it needs cool weather and higher rainfall; higher in protein than the others.
Other Names: Common, French, and hog millet, panicum, miliaceum
Scientific Name: Panicum miliaceum
Main Area of Production: Central Asia, USSR
Important Characteristics: Used mainly as a short-duration emergency crop or irrigated crop.
Scientific Name: Eragrostis abyssinica
Main Area of Production: Mainly the Ethiopian and East African highlands up to 2700 m where it is an important staple food.
Japanese or Barnyard Millet
Other Names: Sanwa or shame millet
Scientific Name: Echinochloa crusgalli, E. frumentacea
Main Areas of Production India, East Asia, parts of Africa; also in the Eastern U.S. as a forage Important Characteristics: Wide adaptation in terms of soils and moisture; takes longer to mature (three to four months total) than the others.
Scientific Name: Setaria italica
Main Area of Production: Near East, mainland China
Important Characteristics. Very drought-resistant.
Average millet yields in West Africa range from about 300-700 kg/ ha. They tend to be low due to marginal growing conditions and the relative lack of information concerning improved practice. Compared to maize, sorghum, and peanuts, research efforts with millet have only yielded 1000-1500 kg/ha and improved varieties have produced up to 20003500 kg/ha.
Climatic Requirements of Millet Rainfall: Pearl millet is the most important cereal grain of the northern savanna and Sahel region of Africa. It is more drought resistant than sorghum and can be grown as far north as the 200-250 mm rainfall belt in the Sahel where varieties of 55-65 days maturity are grown to take advantage of the short rainy season. Although pearl millet uses water more efficiently and yields more than other cereals (including sorghum) under high temperatures, marginal rainfall, sub-optimum soil fertility, and a short rainy season, it does lack sorghum's tolerance to flooding.
Soil: Pearl millet withstands soil salinity and alkaline conditions fairly well. (For more information on salinity and alkalinity problems, refer to Peace Corps, Soils, Crops, and Fertilizer Manual, 1980 edition.) It is also less susceptible than sorghum to boring insects and weeds, but shares sorghum's susceptibility to losses from bird feeding, which damages the maturing crop.
Nutritional Value and Uses of Millet
Pearl, foxtail, and prove millets all contain about 12 to 14 percent protein which is somewhat higher than most other cereals. The most common method of preparing pearl millet in West Africa is as "kus-kus" or "to", a thick paste made by mixing millet flour with boiling water. Millet is used also to make beer. The stalks and leaves are an important livestock forage and also serve as fuel, fencing, and building material. Traditional Pearl Millet Growing Practices in West Africa
The traditional West African pearl millet varieties are generally
2.5-4.0 m tall with thick stems and a poor harvest index. They are usually planted in clumps about a meter or so apart, very often in combination with one to three of the other reference crops, usually sorghum, cowpeas, and groundnuts. Many seeds are sown per clump, followed by a laborious thinning of the seedlings about two to three weeks later. The tiny millet seeds are low in food reserves which become exhausted before the seedlings can produce enough leaf area for efficient photosynthesis and enough roots for good nutrient intake. Therefore, as with sorghum, the growth rate is very slow for the first few weeks. Two general classes of pearl millet are traditionally grown in West Africa:
Â· The Gero class whose varieties are 1.5-3.0 m tall, early maturing (75-100 days), and neutral or only slightly photosensitive in daylength response. In some parts of the savanna, these short-season Geros mature at the peak of the wet season, but have good resistance to the fungal seedhead molds and insects favored by the rains. The Geros make up about 80 percent of the region's millet and are preferred for their higher yields and shorter maturity over the Maiwa class. They mature in July-August in the Guinea savanna and AugustSeptember in the Sudan savanna.
Â· The Maiwa class is taller (35 m). later maturing (120 - 280 days), and much more photosensitive in daylength response than the Gero group. As with the photosensitive sorghum varieties, the Maiwas will not flower until at or near the end of the rains, which allows them to escape serious head mold and insect damage. However, they yield less than the Geros and account for only about 20 percent of the region's millet. In the higher rainfall portions of the savanna 500-600 mm per year where both millet and sorghum can be grown, farmers usually prefer to plant photosensitive sorghum varieties. These have about the same length of growing period, but yield more than the Maiwas due to a longer grainfilling period. However, the Maiwas are favored over the sorghums on sandier soils with lower water storage ability. Some farmers will also choose the Maiwas over the sorghums because the former mature slightly sooner, thus spreading out the harvest labor demands for these late season crops. (The Maiwas are harvested a month or so into the dry season.)
Many of the traditional millets produce abundant tillers (side shoots produced from the plant's crown). However, this tillering is non-synchronous, that is, tillering development lags behind that of the main stem. As a result, these secondary shoots mature later than the main stem. If soil moisture remains adequate, two or more smaller harvests can be taken.
Aside from the normal rainfed millet production, the crop is also planted on flood plains or along river borders as the waters begin to recede. This system is referred to as recessional agriculture and also may involve sorghum.
Peanuts (Arachis hypogea)
DISTRIBUTION AND IMPORTANCE
Peanuts are an important cash and staple food crop in much of the developing world, particularly in West Africa and the drier regions of India and Latin America. The developing nations account for some 80 percent of total world production, with two-thirds of this concentrated in the semi-arid tropics. Because of repeated droughts, disease problems, and other factors, Africa's share of the world peanut export market declined from 88 percent in 1968 to 43 percent in 1977, while its share of total production fell from 36 percent to 26 percent during the same period.
Types of Peanuts
There are two broad groups of peanuts:
Â· Virginia group: Plants are either of the spreading type with runners or of the bunch (bush) type. Their branches emerge alternately along the stem rather than in opposed pairs. The Virginia varieties take longer to mature (120140 days in the tropics) than the Spanish-Valencia types and are moderately resistant to Cercospora leaf-spot, a fungal disease that can cause high losses in wet weather unless controlled with fungicides (see Chapter 7). The seeds remain dormant (do not sprout) for as long as 200 days after development, which helps prevent premature sprouting if they are kept too long in the ground before harvest.
Â· Spanish-Valencia group: Plants are of the erect bunch type and non-spreading (no runners). Their branches emerge sequentially (in opposed pairs), and their leaves are lighter green. They have a shorter growing period (90-110 days in warm weather), are highly susceptible to Cercospora leafspot, and have little or no seed dormancy. Pre-harvest sprouting can sometimes be a problem under very wet conditions or delayed harvest. They are generally higher yielding than the Virginia variety if leaf spot is controlled.
Plant breeders have made some promising crosses between these two groups.
Average peanut yields in the developing countries range from about 500-900 kg/ha of unselled nuts, compared with the U.S. average of 2700 kg/ha, based on 1977 FAO data. Farmers participating in yield contests have produced over 6000 kg/ha under irrigation, and yields of 4000-5000 kg/ha are common on experiment station plots throughout the world. Feasible yields for small farmers who use a suitable combination of improved practices are in the range of 17003000 kg/ha, depending on rainfall.
Climatic and Soil Adaption of Peanuts
Rainfall: Peanuts have good drought resistance and heat tolerance. They mature in 90-120 days in warm weather, which makes them especially well suited to the short wet season of the northern savanna zone of West Africa. They can be grown in moister climates if diseases (especially leafspot) can be controlled and if planted so that harvest does not coincide with wet weather.
Temperature: During the vegetative (leaf development) phase temperature has little effect on yields. However, the rate of flowering and pollen viability are greatly influenced by temperatures during flowering (about 35-50 days after emergence). Pod production is adversely affected by temperatures below 24Â°C or above 33Â°C. At 38Â°C, for example, flowering is profuse, but few pods are produced.
Soils: Peanuts do not tolerate waterlogging, so good soil drainage is important. Soils that crust or cake are unsuitable, since penetration of the pegs is unhindered.
Clayey soils can produce good results if well drained, but harvest (digging) losses may be high due to nut detachment if the plants are "lifted" when such soils are dry and hard. On the other hand, harvesting the crop on wet, clayey soils may stain the pods and make them unsuitable for the roasting trade.
Peanuts grow well in acid soils down to about pH 4.8, but do have an unusually high calcium requirement which is usually met by applying gypsum (calcium sulfate). Peanut fertilizer requirements are covered in Chapter 5.
Nutritional Value and Uses of Peanuts
The mature, shelled nuts contain about 28-32 percent protein and vary from 38-47 percent oil in Virginia types to 47-50 percent oil in Spanish types. They are also a good source of B Vitamins and Vitamin E. Although lower in the essential amino acid lysine (a determinant of protein quality) than the other pulses, peanuts are a valuable source of protein.
In the developing nations peanuts are consumed raw, roasted or boiled or used in stews and sauces. The oil is used for cooking and the hulls for fuel, mulching, and improving clayey garden soils.
Commercially, the whole nuts are used for roasting or for peanut butter. Alternatively, the oil is extracted using an expeller (pressing) or solvent method and the remaining peanut meal or cake (about 45 percent protein) is used in poultry and swine rations. Peanut oil is the world's second most popular vegetable oil (after soybean oil) and can also be used to make margarine, soap, and lubricants. The hulls have value as hardboard and building-block components.
Plant Characteristics of Peanuts
Peanuts are legumes and can satisfy all or nearly all of their nitrogen needs through their symbiotic relationship with a species of Rhizobia bacteria. A characteristic of the peanut plant is that the peanuts themselves develop and mature underground.
Peanut Stages of Growth
Depending on variety, peanuts take anywhere from 90-110 days to 120-140 days to mature. The peanut plant will flower about 30-45 days after emergence and will continue flowering for another 30-40 days. The peanuts will then mature about 60 days after flowering.
PHASE I EMERGENCE
Within a day or so after planting in warm, moist soils, the radicle (initial root) emerges and may reach 10-15 cm in length within four to five days. About four to seven days after planting, two cotyledons break the soil surface where they will remain while the stem, branches, and leaves begin to form above them. The plants grow slowly in the early stages and are easily overtaken by ,weeds.
PHASE II - FLOWERING TO POLLINATION
Flowering begins at a very slow rate about 30-45 days after plant emergence and is completed within another 30-40 days. The flowers are self-pollinated, but bees and rain improve fertilization (and therefore kernel production) by "triggering" the flowers and aiding in pollen release. The flowers wither just five to six hours after opening. A plant may produce up to 1000 flowers, but only about one out of five to seven actually produces a mature fruit.
PHASE III - PEG EMERGENCE TO MATURITY
The pegs (stalk-like structures, each containing a future fruit at its tip) begin elongating from the withered flowers about three weeks after pollination and start to penetrate the soil. After the pegs penetrate to a depth of about 2-7 cm, the fruits begin to develop rapidly within about 10 days and reach maturity about 60 days after flowering. Those pegs that form 15 cm ro more above the ground seldom reach the soil and abort.
It is important to note that the fruits do not all mature at the same time, since flowering occurs over a long period. An individual fruit is mature when the seed coats of the kernels are not fonder wrinkled and the veins on the inside of the shell have turned dark brown. Harvesting cannot be delayed until all the fruits have matured or heavy losses will result from pod detachment from the pegs and from premature sprouting (Spanish-Valencia types only). Choice of harvesting date is an important factor in obtaining good yields.
Traditional Peanut Growing Practices
Small farmers in some developing countries, especially in West Africa, often plant peanuts together with one or more other crops such as sorghum, millet, cowpeas, cotton, and vegetables. Whether intercropped or sown alone, peanuts are usually planted on ridges (raised up mounds or beds) about one meter apart; this improves soil drainage and facilitates digging, In the northern savanna areas of West Africa, they are generally planted in June and harvested in September or October. In the southern, higher rainfall sections of the savanna, it is often possible to grow two crops (April or May until August for the first, and August or September to November or December for the second). Most of the local varieties, especially in the more humid areas, are of the Virginia type which has much better leaf-spot resistance.
Common Beans And Cowpeas
Importance and Distribution
Along with peanuts, this group makes up the bulk of the edible ,pulses grown in tropical and subtropical developing nations. Aside from their importance as a protein source, the crops play an important role in the farming systems of these areas:
Â· They are especially well suited to climates with alternating wet and dry seasons.
Â· Being legumes, they are partly to wholly self-sufficient in meeting their nitrogen requirements.
Â· They are the natural partners of the cereals in intercropping and crop rotations (see Chapter 4).
According to FAO estimates for the 1975-77 period, world dry bean production was about 12.4 million tons annually. Latin America accounts for about a third of world production and produces mainly common (kidney) beans which are also the major type grown in East Africa. Cowpeas are the major grain legume (peanuts excluded) of the West Africa savanna zone.
This section deals with common beans and cowpeas (dry beans). In the appendices are similar descriptions of other pulses such as pidgeonpeas, chickpeas, lima beans, mung beans, soybeans, and winged beans.
Common (Kidney) Beans (Phaseolus vulgaris)
Other Names: Field beans, frijoles, haricot beans, string beans (immature stage), snap beans (immature stage).
Bean plant and pod
Bean varieties can be classified according to three basic characteristics - seed color, growth habit, and length of growing period:
1. Seed Color: Most are black or red seeded, and there are usually distinct local preferences regarding color.
2. Growth Habit: Varieties can be erect bush, semi-vining or vining types; the latter have a vigorous climbing ability and require staking or a companion support crop like maize. Bush varieties flower over a short period with no further stem and leaf production afterwards; these are called determinate. The vining types flower over a longer period and continue leaf and stem production; these are called indeterminate. Semi-vining varieties can be of either type. Given their longer flowering period, most indeterminates have uneven pod maturity with the harvest period stretched out over a number of weeks.
3. Growth Period: In warm weather, early varieties can produce mature pods in about 70 days from plant emergence, while medium and late varieties take 90 days or more. Time to first flowering ranges between 30 and 55 days. With some exceptions, the erect busy types reach maturity earlier than the vining indeterminate types. Plant breeders are developing indeterminate varieties with shorter growing periods and more compact maturity.
Climatic Requirements of Beans Rainfall: Common beans are not well suited to very high rainfall areas (such as the humid rainforest zones of tropical Africa) because of increased disease and insect problems. Ideally, planting should be timed so that the latter stages of growth and harvest occur during reasonably dry weather.
Temperature: Compared to sorghum and millet, beans do not tolerate extreme heat or moisture stress well. Few varieties are adapted to daily mean temperatures (average of daily high and low) over 28 C or below 14 C. Optimum temperatures for flowering and pod set is a daytime high of 29.5Â°C and a nighttime low of 21 C. Blossom drop becomes serious over 36 C and is aggravated also by heavy downpours.
Soil: The plants are very susceptible to fungal root rot diseases, and good drainage is very important. They usually grow poorly in acid soils much below pH 5.6, since they are especially sensitive to the high levels of soluble manganese and aluminum which often occur at the lower pH levels.
Daylength: Unlike some sorghums and millets, most beans types show little response to daylength variations.
Nutritional Value and Uses of Beans
Common beans contain about 22 percent protein on a dry seed basis. They provide adequate protein quality and quantity for older children and adults if eaten in the proper proportion with cereals (about a 2:1 grain:pulse ratio. In the green bean form, they provide little protein, but are a good source of Vitamin A. The leaves can be eaten like spinach and also are used as livestock forage.
Cowpeas ( Vigna sinensis, V. unguiculata, V. sesquipedalia)
Other Names: Black-eyed peas, southern peas, crowder peas.
Cowpeas have much the same variations in seed color, growth habit, and length of growing period as common beans except that cowpea seeds are usually brown or white. There are three separate species:
Â· Vigna Sinensis: the common cowpea in Africa and most of Latin America. The large, white seeded types are preferred in most of West Africa.
Â· Vigna unguiculata: catjung cowpea, a primitive type found mainly in Asia, but also in Africa.
Â· Vigna sesquipedalia: the asparagus or yardlong bean widely grown in Asia mainly for its immature pods.
Most traditional varieties tend to be late maturing (up to five months' and vining Improved bush (little or no vining) types are available and capable of producing good yields in 80-90 days.
Growing Practices and Yields of Cowpeas
Traditional practices and yield constraints of cowpeas are similar to those of common beans. Average yields in the developing countries run from 400-700 kg/ha of dry seed, compared to a California (U.S.) average of about 2200 kg/ha under irrigation. Field trial yields in Africa and Latin America are largely in the 1500-2000 kg/ha range with some over 3000 kg/ha.
CLIMATIC REQUIREMENTS OF COWPEAS
Rainfall: Cowpeas are the major grain legume (peanuts excluded) of the West African savanna (zone). However, they also are grown in many other regions. They have better heat and drought tolerance than common beans, but the dry seed does not store as well and is very susceptible to attacks by weevils (see Chapter 7).
High daytime temperatures have little effect on vegetative growth but will reduce yields if they occur after flowering. High temperatures at this time can cause the leaves to senesce (die off) more quickly, shortening the length of the podfilling period. High temperatures will also increase the amount of blossom drop. As with common beans and most crops, humid, rainy weather increases disease and insect problems. Dry weather is needed during the final stages of growth and harvest to minimize pod rots and other diseases.
Soil: Cowpeas grow well on a wide variety of soils (if they are well drained) and are more tolerant of soil acidity than common beans.
Nutritional Value and Uses of Cowpeas
The dry seeds contain about 22-24 percent protein. The immature seeds and green pods also are eaten. They are considerably lower in protein than the mature seeds, but are an excellent source of Vitamin A while green, as are the young shoots and leaves. The plants are a good livestock forage and are sometimes grown as a green manure and cover crop (see Chapter 5).
Increasing reference crop production
There are basically four ways of increasing the production of the reference crops:
Â· Improving existing cropland
Â· Extending cultivation to new, uncropped areas
Â· Improving the infrastructure
Â· Establishing crop improvement programs.
Any meaningful production increase will require varying emphasis on all four methods.
Improving Existing Cropland
Unquestionably, improved drainage (by land leveling, runoff canals or underground tile drains) and erosion control are high-gain investments. Erosion control not only reduces soil losses and yield deterioration, but in many cases actually improves production by increasing the amount of rainfall retained by the soil.
In the case of irrigation projects, however, the results are often mixed. Many irrigation projects have paid little attention to the potential environmental damage or to the technical problems and soil types involved. Huge dams and artificial lakes have definite appeal on paper, but have often led to drainage and salt accumulation problems, as well as to weed-choked canals and serious health hazards like malaria and schistosomiasis (bilharsia).
Pumping projects relying on wells face similar problems and can seriously lower the water table to the point of endangering the supply. Water alone is not enough to assure profitable yields which must be high to cover the added costs of irrigation. Unless such projects are carefully planned and combined with a crop improvement program, the results are likely to be disappointing.
Extending Cultivation To New Areas
The FAO estimates that total world food production increased by about 50 percent from 1963-76, while cultivated land area grew by only two percent. Estimates concerning the amount of additional cultivable land differ considerably, but suggest that the world as a whole is utilizing only about onethird to one-half of actual and potential arable land (suitable for crops or for livestock). The largest areas of "new" land are in the lowland tropics of Latin America, Africa, and Southeast Asia. There are, however some drawbacks:
Â· Only a small percentage of these lands are capable of sustaining intensive agriculture because of soil or climate factors; an alarming proportion has been claimed by land speculators or is being divided up into ranches by investors, as in Brazil.
Â· Whether in high rainfall or in arid regions, much of this land is prone to accelerated erosion or irrigation-induced salinization (accumulation of salts at the soil surface).
Â· As we have seen, most of the reference crops are not well adapted to high rainfall and humidity. Pasture and perennial crops may be the best choices under these constraints.
Improving the Infrastructure
In agriculture, the infrastructure refers to those installations, facilities, inputs, and services that encourage production. The most important of these are:
Â· Roads and transport
Â· Markets and marketing standards
Â· Storage facilities
Â· Improvements to land such as drainage, erosion control, and irrigation
Â· Yield-increasing technology
Â· A viable extension service
Â· Availability of agricultural machinery and equipment
Â· Political stability
Â· An equitable land tenure and distribution system
Â· National planning for agricultural development
Â· Crop prices that encourage increased output
The small farmers in most areas of the developing world do not enjoy the same access that larger farmers do to these essential factors of production. Agricultural public works projects such as irrigation, flood control, and farm-to-market roads are usually undertaken according to pure economic feasibility or in response to special interest groups. Larger farmers in a number of developing countries, especially in Latin America, are often organized into producer's associations with very effective lobbying powers.
Inequities in land tenure and distribution can have tremendous social and economic consequences and can effectively dampen farming incentives for those affected. In El Salvador, 19 percent of the farms occupy about 48 percent of the land and belong to wealthy "latifundistas" (ranch-type farmers) who grow cotton, coffee, and sugarcane, frequently on an absentee basis. These farms are concentrated on the country's best soil, while the "campesinos" (small farmers) are restricted to the eroded and rocky hillsides where they grow maize, sorghum, and beans. About 47 percent of the country's farms are smaller than 2.47 acres (one hectare) and occupy only four percent of the total land. The majority of the farm units in El Salvador, Guatemala, and Peru have been designated as sub-family.
While the implementation of most other infrastructural essentials is hindered mainly by insufficient capital, land reform faces heavy political obstacles and in some cases is not feasible in terms of land supplies. Furthermore, when small farmers purchase land in densely populated regions like the Guatemala Highlands, the Cibao area of the Dominican Republic, and the lake region of Bolivia, competition frequently drives land prices too high for farming to be economical.
Crop Improvement Programs
More than any other single factor, the development of yieldimproving technology associated with the crop improvement programs of the national and international research institutes will play the mayor role in increasing the yields of the reference crops in the developing countries.
Reference crop improvement programs
The term "crop improvement" is a broad one and refers to any attempt to improve crop yields, quality, palatability or other characteristics through plant breeding or the development of improved growing, harvest, and storage practices. The most successful efforts are well-organized, multidisciplinary (involving several relevant skill areas such as entomology and soil fertility), and crop-specific and aim at developing a "package" of improved practices centered around highyielding, adapted varieties.
A large number of yield-determining factors and crop characteristics can be at least partially manipulated or controlled by plant breeding and improved production practices' as shown in the table on the next page.
Farming Practices Affecting Crop Yields and/or Quality
Â· Method of land preparation (type of tillage and seedbed)
Â· Fertilizer use (kind, amount, timing, placement)
Â· Variety selection Plant density and spacing
Â· Water management (soil drainage, erosion control, moisture conservation practices)
Â· Control of weeds, insects, diseases, nematodes, and birds by chemical or nonchemical methods Adjustment of soil pH
Â· Control of soil compaction due to equipment or animals
Â· Cropping system (monoculture yersus intercropping; crop rotation)
Â· Harvesting, drying, and storage methods
In contrast to the production factors listed above there are a number of others largely beyond the control of both the farmer and the crop improvement worker. These include such variables as the weather and certain soil characteristics (i.e. texture, depth, filth).
Crop improvement programs for individual crops
Potential for Improvement
Of all the reference crops, maize has the highest yield poten tial in terms of grain production per unit of land area under conditions of adequate moisture and improved practices. Maize is generally less troubled by insects and diseases than the pulses, especially beans and cowpeas. In addition, more breeding work has been done with maize than any other major food crop.
Success of control attained by plant breeding and improved crop production - Control Attained
Current Research Activities and Crop Programs
The International Maize and Wheat Improvement Center (CIMMYT)* in Mexico is the institute most involved in maize improvement and acts as the caretaker and shipping agent for the world's most complete collection of maize germplasm (plant genetic material). It cooperates extensively with the International Institute for Tropical Agriculture (IITA) in Nigeria and The International Center for Tropical Agriculture in Columbia (CIAT) in their respective maize programs as well as with national improvement programs throughout the developing world. In 1979, CIMMYT sponsored international maize variety trials in 84 countries at 626 sites to compare its varieties with those from local and other foreign sources.
The CIMMYT-developed varieties originate from a well-organized breeding program. During the 1970s the center developed 34 germ plasm pools (genetic groups) classified according to three climate types (tropical lowland, tropical highland, and temperate), four grain types (flint, dent, white, yellow), and three lengths of maturity (early, medium, late). Advanced lines are developed from these pools by selecting for yield, uniformity, height, maturity, and resistance to diseases, insects, and lodging (tipping over). They are then grown at a number of locations in Mexico. The most promising are used in preliminary international trials, and the best of these become experimental varieties for more extensive trial work overseas.
Spreading Improvement Practices for Maize
From 1961-77, total maize production in the developing countries rose by 66 percent, while acreage increased by 33 percent and yields by 24 percent. However, on an individual country basis, only about half the developing countries have made significant gains (1979 CIMMYT Annual Report). The bulk of adaptive research work with maize in the developing countries has occurred in certain areas of Latin America. Africa and Asia, however, have location-specific growing problems in terms of soils, climate, insects, and diseases for which varieties and improved practices still must be developed. The CIMMYT is presently cooperating with national maize programs in Tanzania, Zaire, Ghana, Egypt and Pakistan as well as Guatemala and is providing staff support to most of them. In addition, it cooperates on a regional basis with Central America and the Caribbean, South and Southeast Asia (11 countries), and the Andean zone (Bolivia, Colombia, Ecuador, Peru, and Venezuela all grain importing countries).
Disease and insect resistance is a top priority at CIMMYT. This organization has a cooperative breeding program with six national maize programs (Thailand, the Philippines, Tanzania, Zaire, Nicaragua, and El Salvador) to develop resistance to downy mildew (important in Asia and spreading to other regions), maize streak virus (Africa), and corn stunt virus (tropical Latin America).
Maize Production Achievements
The Puebla Project in Mexico was the first large-scale attempt to improve small-farmer maize production.
Under CIMMYT administration, the project involved 47,000 farm families in a highland region of Puebla State. Average farm size in the project area was 2.7 ha, operating mainly under dryland (non-irrigated) conditions. Several "packages" of improved practices were developed to suit varying climatic and soil conditions in the zone, and adequate support and delivery systems were sought for the needed inputs, including agricultural credit. By 1972, maize production had increased in the project area by some 30 percent and average family income had increased by 24 percent in real terms. Rural employment was also favorably affected due to an increase in labor needed for every hectare of maize.
The Puebla Project was innovative in moving the "Green Revolution" (the first organized attempt to develop yield improving practices for staple food crops in developing countries) off the experiment station and into the field and in concentrating on dryland rather than irrigated farming.
Similar examples exist in many other developing countries. Experimental plots frequently yield over 6000 kg/ha and it is generally agreed that 3000 kg/ha or more is a reasonable yield goal for small farmers in most regions. Since the real test of an improved variety is its performance under actual farm conditions, CIMMYT is encouraging the cooperating countries to run extensive trials on farmers' fields rather than confining them to the experiment station where conditions are often unrealistically ideal. On the Horizon: Scientists have been working on breeding a nitrogenfixing ability similar to that of legumes into maize. By 1985, they hope to have experimental varieties capable of satisfying up to 10 percent of their nitrogen requirements.
Potential for Improvement
Yields of grain sorghum are generally not as spectacular as those of maize, since the crop is often grown under less than ideal conditions. Sorghum's advantage over maize is its much better yield stability over a wider range of climatic conditions, especially under high temperature and low rainfall. Many of the traditional varieties in the semi-arid tropics are overly tall, are photosensitive, and have an excessive ratio of stalk and leaves to grain. Their delayed flowering enables them to escape serious grain head mold problems and insect damage, but often there is too little soil moisture for grain development which takes place at the start of the dry season. These factors, along with poor management and the large plants' intolerance to healthy plant densities (populations), account for low yields averaging around 600-900 kg/ha in the semi-arid tropics.
Current Research Activities and Crop Programs
The International Crops Research Institute for the Semiarid Tropics (ICRISAT), located in Andhra Pradesh, India, is the major international institute engaged in sorghum improvement. Some of its major goals include the development of varieties with little or no photosensitivity. These varieties would have a shorter growing season and be better adapted for drier areas or shallow soils with low water holding capacity. They would be planted later, but flower about two weeks earlier than traditional types and therefore need good head mold resistance for maturing under more humid conditions. Plant height would be about 2.0-2.5 meters with a better ratio of grain to stalk and leaves. Since sorghum plants are an important livestock forage in much of the semiarid tropics dwarf varieties like those used in the U.S. would not be acceptable. The new varieties would mature in 90-120 days.
Also under consideration are plants with heavy tillering ability to allow compensation for low plant populations and a variety with resistance to striga (a serious parasitic weed, see Chapter 6), sorghum midge, sorghum shoot fly (see Chapter 6) and drought. Work is also being done to develop more coldtolerant varieties for highland or cool-season tropical conditions, and plants with improved disease resistance, especially to downy mildew, charcoal rot, smuts, anthracnose, and rust 'see Chapter 6). Finally, the institute hopes to develop a hi-lysine and higher protein sorghum that has better cooking quality and palatability.
Spreading Improvement Practices for Sorghum
In the southern savanna region of West Africa, improved photosensitive varieties have yielded over 3500 kg/ha in 120-140 days, some two months less than local varieties. They can be sown later in the wet season and will flower about 8-14 days earlier than the local types, thus assuring better moisture availability for grain filling.
As of yet, highly photoinsensitive (day neutral) varieties with good head mold resistance hay e not been developed. There are improved types of this class that are available with 90-120 day maturities, but their planting must be scheduled late enough in the wet season so that the grain fill period occurs at the start of the dry season to avoid head mold. This, however, subjects them to probable moisture stress
Improvements in sorghum protein: In 1974 two lines of sorghum with 30 percent more protein and double the lysine of conventional types were discovered in Ethiopia. However, these lines suffer from some of the same drawbacks as hi-lysine maize in that the grain has a soft starch, floury endosperm (the major portion of the seed surrounding the germ Lembryol) that is very susceptible to storage insects and to breakage under grain threshing using animal trampling. Also, studies have shown these extra protein benefits to vary greatly under different environmental conditions. For example, low soil nitrogen content can cause both the lysine and protein percentage to drop to normal levels. It may be 1985 or later before such improved nutrition varieties are released.
Nitrogen-fixing ability: As with maize, attempts to breed some nitrogen-fixing ability into sorghum are only in the early experimental stages.
Production improvements and the future: Sorghum lags behind maize in successful on-farm yield improvement campaigns. Most successes have occurred in the less marginal rainfall areas. For example, although high-yielding sorghum varieties were released in India in the mid-60's, they spread little beyond regions with assured rainfall or irrigation. A mayor factor is the highly variable climatic environment of the semi-arid topics where standardized technology packages have only limited suitability, thus requiring greater adaptive research efforts. However, organized efforts at sorghum improvement are much more recent than those for maize, and the future does look promising.
Potential for Improvement
Millet yields are generally lower than those of sorghum due to harsher growing conditions and a shorter period of grain filling. Traditional West African varieties have major limiting factors such as poor plant architecture. They tend to be overly tall and have a poor harvest index.) In addition, the photosensitive types often flower too late in the season, causing moisture stress during grain filling. Those varieties which are not as affected by daylength (the Geros) have moderate tillering ability, but it is not synchronous with the main stem. Thus, most of the tillers flower too late, when moisture is not adequate for grain filling.
Current Research Activities and Crop Problems
The ICRISAT breeding program concentrates mostly on pearl millet, and it aims at improved drought, insect, and disease resistance, increased response to improved practices, better harvest index, and varieties with a range of maturities to suit varying rainfall patterns. It is selecting also for varieties particularly suited to intercropping combinations. Protein content and early seedling vigor are other concerns.
In West Africa and the Sudan ICRISAT has a program to develop high-yielding sorghum and millet varieties. This cooperative program includes the countries of Mali, Upper Volta, Niger, Ghana, Chad, The Gambia, Senegal, Nigeria, Mauritania, Cameroon, and Benin.
Achievements in Millet Improvement
As with sorghum , millet improvement efforts in the developing countries are relatively recent and at an early stage. The ICRISAT trials in West Africa during 1976 and 1977 showed that new varieties were not much better than the existing West African types with a few exceptions. The major problem was lack of disease resistance and overly early maturity. On the other hand, breeding efforts in Senegal have produced high-yielding dwarf types capable of better fertilizer response. These have an improved harvest index and a maturity range of 75-100 days. Some of the best ICRISAT varieties have yielded up to 4000 kg/ha in international trials. Progress also is being made in the development of varieties with good resistance to downy mildew (Sclerospora graminicola), a serious fungus disease encouraged by high humidity. As with maize and sorghum, attempts are being made to develop some limited nitrogen-fixing ability in millet, but results are at least four to five years away.
On the Horizon: Millet production should expand significantly in the future as more marginal rainfall land is brought under cultivation. Further research is expected to make the millets one of the most productive cereals on a yield per area per time basis (yield of crop in a certain area per cropping cycle per year).
Potential for Improvement
When grown under ideal moisture conditions, peanut and other pulse crop yields are about one-third to one-half those of maize. However, since peanuts are about three times higher in protein than maize, the yields are actually very similar on a protein per area basis (a 2000 kg/ha peanut crop produces about the same total amount of protein as a 6000 kg/ha maize crop). This is also the case with the other pulses, all of which have two to three times more protein than the cereals. In short, the pulses are geared more to producing modest yields of high protein seed rather than high yields of starchy seed as with the cereals. Although the lower yields of the pulses should be kept in mind, there is potential for yield improvement in the developing countries where production per hectare lags considerably behind that of the developed countries.
Research Activities and Crop Improvement
Since peanuts are selfpollinated, the development of new varieties by crossing is difficult and time-consuming. The individual flowers must be manually emasculated and then hand pollinated. Since seed production per plant is comparatively low, multiplication of improved types is very slow, although they can be propagated by cuttings.
Most efforts concentrate on collecting and improving local and introduced varieties by selecting for adaptability, drought resistance, oil and protein content, disease and insect resistance, and shelling percentage (ratio of shell weight to kernel weight).
Spreading Peanut Improvement Activities
The major international institute involved with peanut improvement in the developing countries is ICRISAT. Advanced work is also being done in several of the developed countries such as the U.S. (especially Georgia, North Carolina, and Texas), Australia, and South Africa, but it is designed to serve their local conditions. Other centers of peanut improvement are Senegal, Nigeria, the Sudan, Mexico, Argentina, and Brazil.
Breeding for earliness to suit short rainy seasons, seed dormancy (to prevent in-ground sprouting), and resistance to rust, leaf spot, and aflatoxin (see Chapter 6) are all being conducted by ICRISAT. Work in Senegal has developed several lines resistant to rosette virus, a serious problem in the wetter peanut zones of Africa.
Of the reference crops, peanuts are the most complicated in terms of growing and harvesting practices needed for good yields. Seed bed preparation, weed and disease control, and harvesting require particular attention to detail and timeliness. Being a much higher value crop than the cereals, repeated applications of foliar fungicides for leaf spot control have a good cost-benefit ratio and are another example of the relative sophistication required for good yields. Undoubtedly, plant breeding has a role to play in peanut improvement, but improved management practices are particularly important for boosting yields.
In those developing countries where peanuts are a major export crop, marketing is usually controlled by a government board, which also provides storage facilities and may act as a supplier of seed, fertilizer and other inputs. Under these condicions, adaptive research work is also given greater priority, but the weak link is also the extension system, which must bridge the gap between the farmer and the experiment station. In general, yields are far below the 1700-300 kg/ha range that is feasible under improved practices where moisture stress is not serious.
Beans and Cowpeas
Until the early 1970s, pulse improvement had been largely neglected. Compared to the cereals, these grain legumes seemed to offer less promising opportunities due to their relatively low yields and greater susceptiblity to insects and diseases. However, in view of their high protein contents and potential as nutritional complements to the cereals, research and extension programs can no longer afford to ignore them. The best yields of the cereals and the pulses are fairly similar when compared on a protein produced per area basis.
Potential for Improvement
Early research seemed to suggest that common beans were one of the least productive of the pulses. However, a comparative growth study by the International Center for Tropical Agriculture (CIAT) in 1978 involving five grain legumes showed that common beans and cowpeas were the two most efficient on a yield per day of growth basis (the other three involved were pigeon-peas, soybeans, and mung beans).
Unfortunately, current average yield for Africa and Latin America are a low 600 kg/ha, while CIAT has obtained up to 4300 kg/ha under monocropping (beans as the sole crop) and 3000 kg/ha in mixed plantings with maize.
Current Research Activities and Crop Programs
The major international institute involved in common bean improvement is CIAT. In 1973 they established a Bean Production Systems Program to increase the production and consumption of the crop in Latin America. In addition it also cooperates with developing countries in other areas. This effort is now being supplemented by a recently organized U.S. government-sponsored program for cooperative dry bean research between U.S. universities and developing countries.
The CIAT program aims to increase bean yields through several methods:
Â· Development of improved varieties resistant to major diseases and several stress factors like low soil phosphorus, soil acidity, drought, and temperature extremes. Special attention is being given to mixed cropping with maize.
Â· Breeding for improved nitrogen fixation. Currently, common beans are one of the more inefficient nitrogen fixers and require moderate rates of supplemental fertilizer.
Â· Developing improved management practices for both monoculture and mixed cropping systems (see chapter 4).
Â· Training personnel from national programs in other developing countries and developing a strong bean research network in Latin America and East Africa.
As part of its international trials program, CIAT maintains an International Bean Yield and Adaptation Nursery (IBYAN), consisting of 100 entries. This IBYAN is replicated by CIAT and shipped to many other countries to be used in their experimental work with beans. The Center for Tropical Agriculture, Research, and Training (CATIE) in Turrialba, Costa Rica also is involved in bean improvement work.
Spreading Bean Improvement Practices
After nearly some five years of breeding work, most of the improved varieties CIAT sent out for international trials in 1979 carried some resistance to major pest problems like common mosaic virus, rust, common bacterial blight, angular leaf spot, anthracnose, and a damaging species of leafhopper (Empoasca Kraemeri) prevalent in Latin America. Strains were found also that showed some tolerance to low levels of soil phosphorus and to aluminum and manganese toxicity which often affects bean in highly acidic soil (much below pH 5.5). Both CIAT and CATIE have made significant progress in improving bean-maize multiple cropping systems through improved management and bean variety development.
Due to the relatively recent interest in bean research, on-farm yield improvement programs have made nowhere near the impressive and widespread gains of maize, rice, and wheat. However, research achievements in breeding and management are at the point where farmers can increase their yields with a well-organized extension program.
Progress in Cowpea Improvement
The International Institute for Tropical Agriculture (IITA) in Nigeria is the mayor international institute involved in cowpea improvement and is working toward good pest resistance, improved yields, and the development of a package of improved practices for cowpeas under multiple cropping conditions common in tropical Africa. By 1978, IITA had released a total of five new strains (VITA 1-5) with better yield and pest resistance and a good protein content. They are capable of producing 1500-2500 kg/ha under small-farmer improved management, compared to the current West African average of around 500 kg/ha. The creamy white seed color of VITA 5 is favored in much of Africa. As with common beans, on-farm yield improvement extension efforts are still in their early stages.