|Traditional Field Crops (Peace Corps, 1981, 283 p.)|
|Planning and preparation|
The Goals of Successful Planting
When planting, farmers must accomplish four objectives in order to promote good crop yields:
1. Attain an adequate stand (population) of plants. This requires seed with good germination ability, adequate land preparation, sufficient soil moisture, correct planter calibration (adjustment) if mechanical planters are used, proper planting depth, and control of soil insects and diseases that attack seeds and young seedlings. In some areas, birds and rodents also cause problems.
2. Attain the desired plant spacing both in the row and between the rows.
3. Observe timeliness in land preparation and planting. The right time to plant depends on the crop's characteristics (i.e., peanuts should be planted so that harvesting will be likely to occur during reasonably dry weather), the onset of the rains and overall rainfall pattern, the influence, if any, of planting date on insect and disease problems such as sorghum head mold.
4. Use the right type of seedbed for the particular crop, soil, and climate (see page _).
Planting Methods And Equipment
1. Hand planting with a planting stick, hoe or machete: This is the most common method used by small farmers in the developing world.
· Equipment costs are negligible.
· Less thorough seedbed preparation is needed than for most mechanical planters. The farmer who hand plants can push large clods out of the way while walking down the row or can plant directly into untilled soil.
· Time and labor requirements are high: it takes three or four person-days to plant a hectare by hand.
· When hand planting, farmers usually put several seeds in each hole and space the holes rather far apart, partly to save labor. This practice can often reduce yields by resulting in too low an overall seeding rate and too much competition among the plants that emerge from the same hole.
2. Improvements in Hand Planting
· Hand-operated, mechanical "punch" or "jab" planters are available that make the planting holes and drop in the seed in one movement (the seed is automatically metered out from a reservoir). They are operated like an ordinary planting stick (jabbed or punched into the ground) but are much quicker and are also very useful for filling in any "skips" (vacancies) in larger fields. A hectare of maize can be planted in 15-20 personhours. The farming systems program of IITA in Nigeria has designed a very successful punch planter suitable for planting maize, sorghum, cowpeas, beans, and soybeans into untilled ground. It is also capable of planting through a dried mulch. The IITA punch planter can be built in a workshop with access to metal shears (no welding is needed). (Write IITA for plans.) Other types of punch planters are available commercially in some countries.
· Hand-pushed planters: Most models require a fairly loose clod-free seedbed for satisfactory operation. However, IITA's farming systems program has designed a very effective rolling punch planter (called a rotary injection planter, see illustration) that can be built in any workshop with welding and metal-shearing capabilities and is being manufactured by Geest Overseas Mechanization Ltd., West Marsh Road, Spalding, Lincolnshire PE11-2BD, England (price is about $225 U.S.). The rotary injection planter uses the same principles as the hand punch planter, but has six punchinjection devices on a rolling wheel plus a following press wheel to firm down the seed row. The standard design produces a seed spacing of 25 cm, but alternate rollers can be made for different spacings. The rotary injection planter is also available as a four-row, hand-pulled model for planting direct-seeded rice.
· Hand planting into furrows made with an animal- or tractordrawn implement: A wooden plow, cultivator shank or other implement can be used to make seed furrows in plowed ground. If certain precautions are followed, the fertilizer can be placed in the same furrow (see page 157).
· Reasonably parallel crop rows are required if weeding is to be done with an animal- or tractor-drawn cultivator. Farmers can easily construct a parallel row "tracer" consisting of a wood or bamboo frame with hardwood or steel teeth for marking out rows. (A design for this handy implement can be found in the Peace Corps' Animal Traction manual.)
· Improved seed-spacing accuracy can be achieved by running a rope or chain down the row with knots or paint marks to indicate the proper spacing. Otherwise, farmers commonly make large errors in spacing when using planting sticks or dribbling out seeds into a plowed furrow.
3. Animal- and tractor-drawn mechanical planters are available in many different models. A farmer using a onerow animal-drawn planter can sow about 1-1.5 ha in a day and about 5-8 ha using a two-row tractor-drawn planter.
Here are some important considerations concerning these types of planters:
· Most mechanical planters require a more thoroughly prepared seedbed than is needed for hand planting. Some models have special soil openers that permit satisfactory operation in hard or cloddy soil.
An animal-drawn planter with a separate hopper for banding fertilizer
The IITA designed hand-operated "jab" or "punch" planter, which can be made in a workshop. The attached metal bracket firms the soil over the seed and spaces the next seed insertion.
The rolling "punch" planter developed by IITA and now manufactured commercially. It also can be built in a workshop.
A hand-pushed fertilizer band applicator. This model places the fertilizer below the soil surface, which is essential for phosphorusbearing fertilizers. The attachment at the left is used to close the furrow but usually is not needed.
· The farmer must be able to calibrate (adjust) the planter so that it drops the seeds at the correct intervals along the row (see page 135).
· Some models have attachments for applying fertilizer in a band beneath the soil and slightly to the side of the seed row. This is an especially effective method for fertilizers containing phosphorous.
Farmers using planters without fertilizer applicators will often broadcast the fertilizer and plow it under before planting or leave it on top of the ground; this should not be done with fertilizers containing phosphorus! Farmers buying mechanical planters should be encouraged to purchase a fertilizer attachment if available and effective. (NOTE: The applicator should not dribble the fertilizer on top of the ground or place it in direct contact with the seed.)
Plant Population And Spacing
Both plant population and spacing affect the yields of the reference crops, and extension workers should understand the relationships.
Plant Population and Its Effects on Crop Yields
· Up to a point, crop yields will increase along with increases in plant population until the competition for sunlight, water, and nutrients becomes too great.
· Excessively high populations will reduce yields, encourage diseases, and seriously increase lodging in maize, sorghum and millet by promoting spindly, weak stalks.
· Excessively low plant populations will cut yields due to unused space and the limitations on maximum yield per plant.
· Under most conditions, changes in plant population will not affect yields as much as might be expected. This is because most crops have a good deal of built-in buffering capacity, especially if the population is too low. In this case, the plants respond by making yieldfavoring changes such as increased tillering (millet, sorghum) and branching (peanuts, other pulses), more pods or ears per plant or larger ears or grain heads. In maize, a plant density that is 40 percent below the optimum for the given conditions may lower yields by only 20 percent.
· Plant population changes have a more pronounced effect under conditions of moisture stress
There is no easy answer to this, because the optimum plant density depends on several factors:
· Type of crop and variety: Because of differences in plant size and architecture, crops and their varieties vary in their tolerance to increasing plant populations. For example, early maturing maize varieties are usually shorter and smaller than later maturing ones and therefore may benefit from higher plant densities. Beans and cowpeas respond well to populations three to four times higher than for maize due to their smaller plant size and a growth habit that favors better light interception.
· Available soil moisture: The optimum plant population density varies directly with rainfall and the possibility of moisture stress. Plant population has a stronger effect on yields under low moisture conditions than when moisture is adequate. This is because increased populations also increase water use, although plant spacing can make a difference. This is particularly true for maize and sorghum, because yields can be significantly reduced by relatively small increases in plant population when grown under moisture stress.
· Available nutrients: Adequate soil fertility is especially essential with high plant populations. In fact, fertilizer response is often disappointing when plant populations are too low for the given conditions. In fact, this is one of the main reasons that small farmers often do not get their money's worth out of fertilizer. An ear of maize can only grow so big, and even high rates of fertilizer can not make up for too few ears produced by a small number of plants.
· Management ability: High populations require more soil fertility and moisture as well as better overall general management.
Plant Spacing and Its Effects on Crop Yields
The reference crops are row crops for some very good reasons. A row arrangement permits quicker and easier weeding and facilitates most other growing operations. Row cropping with its handy space for equipment, animal, and human traffic allows for ease of mechanization and handling, no matter what the level of sophistication. Distributing a given plant population over a field involves both plant spacing within the row and the distance between the rows (row width).
Plant spacing within the row: The number of seeds that need to be planted per meter or foot of row length depends entirely on the plant population and row widths that have been chosen according to recommendations. The main concern then becomes whether hill planting or drill planting should be used. In drill planting mechanical planters drop seeds out one at a time along the row. Small farmers who hand plant their crops usually use hill planting, sowing several seeds per hole and spacing the holes rather far apart. This reduces time and labor and also may improve seedling emergence under crusty soil conditions, but it may lower yields somewhat because of inefficient use of space and increased competition between the plants within a hill for sunlight, water, and nutrients.
Row Width: Space between rows is determined by the type of equipment used as well as by plant size or "spread". The use of tractor-or animal-drawn equipment requires more space between rows (wider row widths) than when only hoes and backpack sprayers are used. Beans can be spaced in narrower rows than maize or other tall crops and still be weeded with an animal-drawn cultivator without knocking the plants down. Row width influences crop yields in four ways:
· As row width is narrowed, the plants can be spaced farther apart within the row and still maintain the same population. Up to a point, this makes for better weed control due to earlier and more effective between-row shading by the crop.
· Narrower rows allow for higher plant populations without overcrowding.
· As row width is widened, plants have to be crowded closer together within the row in order to maintain the same population. This may lower yields.
Should the use of narrower rows be encouraged? Here are some things to consider:
1. Switching from 100 cm to 75 cm rows in maize and sorghum may increase yields by as much as 5-10 percent when total plant population is kept constant.
When grown alone, bush beans and bush cowpeas are ususally planted in narrow rows (45-60 cm) by most small farmers. Under good management and yields, most studies have not shown much advantage to reducing peanut row width below 75-100 cm. Given the marginal moisture conditions under which millet is grown, row widths less than 75-100 cm are unlikely to be advantageous.
2. Row width and moisture use: Although narrower rows cut down water evaporation from the soil surface because of earlier and more complete soil shading, this is often negated by increased plant water use (transpiration) due to better leaf exposure to sunlight. Under low moisture conditions, plant population has a much greater influence on water use than row width.
3. It is doubtful that a 5-10 percent yield increase will have much of an influence on small farmers whose yields are fairly low. Even if yields are good, switching to narrower rows may cause more problems than it is worth:
· Narrow rows cost the farmer more in terms of time, seed, and pesticide. That is because the narrower the row width, the greater the total amount of row length per hectare or other land unit, since there are simply more rows to deal with.
· If tractor-drawn equipment is used, overly narrow rows may increase plant damage from tractor tires and passing equipment as well as increase soil compaction near the row zone. If several crops are being grown under tractor cultivation, it is more convenient to settle on a standard row size rather than be constantly readjusting tire spacing, tire size, and cultivator tine spacing. Remember, too, that row width must be kept wide enough to permit tractor cultivation (weeding). This cannot be done by relying solely on herbicides!
Summary of Plant Population and Spacing Studies Conducted with the Reference Crops
MAIZE: Overly high populations cause increased lodging, barren stalks, unfilled ears, and small ears. Dry, husked ears weighing more than 270-310 g indicate that plant population was probably too low for the conditions and that yields might have been 10-20 percent higher. Ear size of prolific (multiple-ear) varieties will not vary as much with changes in plant density as will single-ear varieties; rather the number of ears per plant will decrease as density increases.
Hill versus drill planting: Numerous trials with maize have shown yield increases of 0-13 percent when drill planting (one seed per hole) was substituted for hill planting at two to three seeds per hole. However, lodging appears to be more of a problem with drill planting. Farmers who are hand planting four to six seeds per hole should be encouraged to switch to two to three seeds per hole and space the holes close enough together to achieve the desired plant population. It is doubtful that switching to drill planting is worth the extra labor involved under hand planting.
Under adequate moisture and fertility, optimum plant populations vary from about 40,000 to 60,000 per hectare. Plant size, management, fertility, and the varietiy's tolerance to plant density and available moisture must be considered when making population changes. Studies also show that overly high populations have a negative effect on maize yields when moisture is low.
SORGHUM: Optimum plant population varies markedly with available water, plant height, tillering ability, and fertility. In varieties that tiller well, plant population is less important than with maize since the plants can compensate for overly low or high populations by varying the production of side shoots.
In West Africa, the improved long-season photosensitive and the improved short-season non-sensitive varieties are sown at the rate of 40,000-80,000/ha under good management; the dwarf photosensitive, long-season varieties are sown at rates of 100,000/ha or more.
All the above populations are based on monoculture.
PEARL MILLET: In West Africa, millet is planted in hills usually a meter or more apart; many seeds are sown per hill, and thinning takes place two or three weeks later. This involves much hand labor and is seldom finished before serious competition has taken place. Trials in Upper Volta by ICRISAT showed that millet germinated best when planted at many seeds per hill and that hill planting outyielded drill planting. However, other ICRISAT work in West Africa showed no difference between yields from hill and drill plantings.
Population and spacing: In West Africa, pearl millets of the Gero type are often interplanted at populations of 7500-8500 plants per hectare with two to three other crops. The taller, long-season Maiwa types are sown at 40,000-80,000 plants/ha when planted alone under good management. For improved dwarf Geros, populations over l00,000/ha are recommended.
Most varieties have a strong tillering ability and adjust themselves to varying densities through changes in tiller production. Within limits, yields are not greatly affected by plant population changes.
PEANUTS: In parts of West Africa, peanuts are frequently interplanted in combination with sorghum, millet, and maize. Because peanuts are the most valuable, the tendency is to keep the cereal population down to about 3000-6000 hills per hectare and the peanut density high at about 30,000 hills per hectare, or about the same as under sole cropping.
In West Africa, the recommended plant population for improved varieties grown alone ranges from about 45,000-100,000/ha. Rows vary from 24-36 inches (60-40 cm) and seed spacing in the row from 15-25 cm. For the Virginia types populations of 45,000-60,000/ha have been found to be optimum, with higher populations recommended for the Spanish-Valencia types.
Early studies in the U.S. in the 1940's and 1950's obtained yield increases of 30-40 percent by switching from row widths of 90 cm to 4560 cm. At that time, however, average yields were relatively low (1550 kg/ha). As yields have increased over the years, the importance of row width has diminished considerably, and most U.S. growers are using 75-95 cm widths with one seed every 10 cm. A stand of one plant every 15-20 cm is felt to be adequate, but overplanting is needed to make up for any losses.
Two new developments may influence row widths: 1) smaller-size, dwarf varieties which will not fully spread out to cover a 90 cm row width. 2) Plant growth regulators like Alar, which are internode shorteners (internodes are the spaces between nodes on the stem and branches) which decrease plant size and are especially suited to runner types.
BEANS: The International Center for Tropical Agriculture (CIAT) studies in Colombia have shown that bush beans grown alone give highest yields in spacings of either 30 cm between rows and 9 cm between plants 45 cm between rows and 60 cm between plants (equivalent to about 400,000 seeds/hectare). A yield plateau is usually reached around 200,000250,000 actual plants per hectare, but stand losses from planting to harvest are often in the 25-40 percent range, meaning that considerable overplanting is necessary. High density plantings also appear to increase the height of the pods from the ground, which lessens rotting problems. However, very narrow rows aggrativate Sclerotium stem rot where it occurs.
Studies by CIAT and the Center for Tropical Agriculture, Research and Training (CATIE) indicate that plant populations for bush beans in the range of 200,000250,000/ha are also ideal when grown together with maize.
Trials with climbing beans show that final plant populations of 100,000-160,000/ha are optimum, whether grown alone with trellising or with maize.
COWPEAS: In West Africa, improved cowpea varieties of the vining type are grown at population densities ranging from 30,000100,000/ha in rows 75-100 cm apart.
CHICKPEAS: An ICRISAT study showed that yields remained relatively stable over wide ranges of plant density (4-100 plants per square meter).
Guidelines for Attaining a Good Stand and The Desired Spacing
Eight key factors largely determine whether a farmer actually ends up with a good stand of plants and the right spacing for the conditions:
· Seed-germination ability
· Percent of overplanting
· Planting depth
· Seedbed condition (clods, moisture, etc.)
· Seedbed type (flat, furrow or ridge planting)
· Accurate measurement when hand planting and calibration of mechanical planters
· Soil insects and diseases
· Fertilizer placement.
Always run a germination test (see page 121 before planting; good seed should test out at close to 90 percent. Up to a point, overplanting will compensate for lower germination, but seed testing below 50 percent germination should not be used since seedling vigor is also likely to be affected.
Percent of Overplanting
No matter how well the seed germinates, the farmer should still overplant to make up for any added plant losses due to insects, diseases, birds, and weeding operations. When using good seed, it is usually a sound practice to overplant by 15-20 percent in order to assure the recommended final stand of plants at harvest. Of the reference crops, beans, cowpeas and peanuts are likely to suffer the greatest plant losses and will usually benefit from even higher overplanting. Much depends on the specific growing conditions. High rates of overplanting (500 percent or more) followed by heavy hand thinning are a standard practice when field planting small vegetable seeds like cabbage, tomatoes, and lettuce. This is not recommended for the reference crops, since their seeds are larger, hardier, and more vigorous in their early growth. Labor and seed costs are excessive with high overplanting and thinning. Millet is commonly thinned in West Africa after being overplanted heavily, but this should be discouraged.
Optimum planting depth varies with the crop, soil type (sandy versus clayey), and soil moisture content. Seeds should be placed deep enough so that moisture is available for germination, but shallow enough so that seedling emergence is not impaired. Local farmers should be regarded as the ultimate authority on the best planting depths, but here are some general guidelines:
· Seeds can be planted deeper in sandy soils than in clayey soils without reducing plant emergence.
· Planting depth should be deeper under low soil moisture conditions.
· Large seeds have more emergence strength than small ones, but this is also affected by the seedling's structure. Maize, millet, and sorghum push thorugh the soil with spikelike tips which aid emergence. Peanuts, beans, and the other pulses emerge in a much more blunt form.
Normal Ranges in Planting Depths for the Reference Crops
Peanuts, Beans, Cowpeas.
Cloddiness and soil moisture will affect germination. Some soils, especially those high in silt, tend to form a hard surface crust when drying out after a rain. This can sometimes seriously reduce emergence, especially for the pulses. If necessary, these crusts can be broken up with a spiketooth harrow or other homemade device.
Seeds should be in reasonably firm contact with moist soil. Most tractor-drawn planters have steel or rubber "press" wheels running behind them to help improve seed and soil contact. (See page 105 for more information on seedbed preparation.)
Most of the crops can be flat-, furrow- or ridge-planted according to the particular soil and climate conditions. Good drainage and freedom from ponding (standing) water is especially vital for peanuts, beans, and cowpeas, which are particularly susceptible to root and stem rots. They should be flat-planted where drainage is good or sown on top of ridges or beds where drainage is poor. If flat-planting, care should be taken not to form a depression along the seed row where water could collect. This is a problem where mechanical planters with heavy press wheels are used, but can be avoided by using wider press wheels and throwing extra soil into the row ahead of the planter with cultivator sweeps.
Planter calibration; accuracy of hand planting
Mechanical planters must be calibrated (adjusted) prior to planting to assure that they space the seeds out correctly.
Hand planting is prone to large errors in row width and seed spacing unless some effort is made to assure accuracy. The use of a planting rope or chain along the row with knots or paint marks to indicate the spacing is recommended.
Soil insects and diseases
Seeds may need to be treated with a fungicide dust to help control seed rots which are especially serious under cool, wet conditions. Seed or soil treatment with an insecticide may also be needed to protect against damage from insects that attack the seeds and young seedlings.
Fertilizer placed too close to the seeds or in contact with them may prevent or seriously reduce germination. This depends on the kind, amount, and placement of the fertilizer (see page 161).