Maize is the most important cereal crop in sub-Saharan Africa. It is a staple food for an estimated 50% of the population. It is an important source of carbohydrate, protein, iron, vitamin B and minerals.
Africans consume maize in a wide variety of ways (porridges, pastes and beer). Green maize, fresh on the cob, is eaten baked, roasted or boiled.
Every part of the maize plant has economic value: the grain, leaves, stalk, tassel, and cob can all be used to produce a large variety of food and non-food products both for humans and animals. In sub-Saharan Africa maize is mostly grown by small-scale farmers, generally for subsistence as part of mixed agricultural systems. The systems often lack inputs such as fertilizer, improved seed, irrigation, and labour.
Maize is also an important livestock feed both as silage and as crop residue, grain and is also used industrially for starch and oil extraction.
Climate conditions, soil and water management
Maize grows well in a range of climatic conditions with its large number of varieties differing in period to maturity. It has a wide range of tolerance to temperature conditions and it is essentially a crop of warm regions where moisture is adequate.
The crop requires an average daily temperature of at least 20°C for adequate growth and development. Optimum temperature for good yields is around 30°C.
The time of flowering is influenced by photoperiod and temperature. It is grown mainly from 50°N to 40°S and from sea level up to 3about 3000 m altitude at the equator. At higher latitudes, up to 58°N, it can be grown for silage but not foe grain production.
Maize is especially sensitive to moisture stress around the time of planting, tasseling and cob formation. In the tropics it does best with 600 – 900 mm of rain during the growing season.
Maize can be grown on many soil types, but performs best on well-drained, well-aerated, deep soils containing adequate organic matter and well supplied with available nutrients. The high yield of maize is a heavy drain on soil nutrients. Maize is often used as a pioneer crop, because of the high physical and chemical demands it makes to the soil. Maize can be grown on soils with a pH from 5 – 8, but 5.5 – 7 is optimal.
Sensitive to salinity.
Since a young crop leaves much of the ground uncovered, soil erosion and water losses can be severe and attention should be paid to adequate soil and water conservation measures.
1. Local seed.
Low to medium yields, usually well sheathed and so more resistant to weevil attack in storage, possibly more palatable to local4 tastes. Example: Kikuyu maize. Exotic varieties of maize can be collected to add genetic diversity when selectively breeding new domestic strains
High yielding but also requiring large amounts of fertiliser. Seed from hybrids cannot be saved for planting so new hybrid seed is required each year.
A typical example here is the “Katumani” and “Coast Composite”. These are stabilized varieties and new seed is not required each year. If proper selection procedures are followed, farmers can use their seeds selected from their harvest as planting material in the next season.
Maize growing zones in Kenya and recommended varieties
Highland Maize Varieties
These varieties are bred and recommended for medium to high altitudes (1500-2400 m) where day temperatures seldom exceed 280°C during growing season and where the night temperatures drop to as low as 80°C. Rainfall requirement ranges from 800-1500 mm. Where similar conditions prevail in the highlands of Tanzania, Uganda and Ethiopia these varieties are recommended. Examples in this group include
ü “H 6210”,
ü “H 6212”,
ü “H 6213”,
ü “H 629” and
ü “KH 600-15A”
Medium Altitude Agro-Ecozone
Altitude range is between 1000 and 1800 m. Some of the varieties in this category include
ü “H 515” and
ü “H 516”.
These varieties are commonly grown in coffee growing belts maturing in 4-5 months. The ideal rainfall amount is between 750-1000 mm
The altitude in this zone falls between 1000 and 1500 m where the temperature ranges from 12 to 300°C and has rainfall similar to that of high altitudes. “Hybrid 624” is a typical example in this category.
Pwani hybrids (“PH 1” and “PH 4”) and “Coast Composite” are fairly short varieties resistant to lodging and more tolerant to moisture stress and recommended for altitude range of 0-1250 m. above sea level with 400 mm of rainfall.
They have an added advantage of good husk cover hence reduced crop loss through bird, weevil attack and ear rots. They are also suitable under inter-cropping systems.
Examples in this category include “Katumani Composite B” and “DLC 1”. The former is a fast growing open pollinated variety, which is fairly short and produces short cobs. It is a drought escaping variety flowering within 60-65 days and maturing within 90-120 days. The variety performs well within altitudinal range of 1000-500 m above sea level and is a variety for marginal rainfall areas. The variety requires 250-500 mm of rain, and has performed extremely well in arid marginal areas in many parts of Africa particularly in Somalia, Ethiopia, Sudan, Tanzania and Namibia
“DLC 1” also open pollinated is recommended for arid and semi-arid regions. This variety flowers earlier than “Katumani Composite B” by about 4-7 days and is shorter but more prolific. Under unfavourable conditions the variety performs better than “Katumani Composite B”. The variety is best suited where rainfall duration is short and amounts to less than 350 mm. The variety is a good substitute where rainfall is erratic and can be recommended for arid marginal areas in the region as “Katumani Composite B”.
PROPAGATION AND PLANTING
Maize is always planted through direct seeding. The planting material for this crop should be sown early in the season, as soon as soil conditions and temperature are favourable. Delayed planting always leads to reduced yields. In Kenya there is a drop of expected yields of 1-2% every day planting is delayed (AIC 2002).
Planting can be done either be hand or be mechanized depending on the scale of production and farmers capability. Hand planting requires 5-10 man-days/ha. Seed is dropped in the plough furrow or in holes made with a planting stick. Planting may be done on hills or in rows, on flat land or on ridges. On heavy soils ridging is advisable, to improve drainage.
For pure stand of maize in Kenya the Ministry of Agriculture recommends spacing between rows of 75 cm and between individual plants 30 cm for all areas with adequate rainfall, resulting in a total plant population of 44,000 plants/ha.
In the coffee zones this can be increased to 75 cm x 25 cm giving total plant population of 53,000 plants/ha. In dry or marginal areas the recommendation is to increase spacing to 90 cm between rows and 30 cm between seeds – total population 37,000 plants /ha. Approximate seed rate is 25 kg/ha. The depth of planting is commonly 3-6 cm, depending on soil conditions and temperature. Deep sowing is recommended on light, dry soils. Animal manure or phosphatic fertilizers are applied at the time of planting.
5Weed control is very important. Maize is very sensitive to weed competition during the first 4-6 weeks after emergence.
It should be planted as soon as possible after the preparation of the seedbed.
Inter-row cultivation to control weeds and to break up a crusted soil surface may be done until the plants reach a height of about 1 m. In Kenya 2 weedings are necessary for most maize varieties, though a third weeding may be necessary for varieties that need 6 to 8 months. Weeding by hand requires a minimum of 25 man-days/ha.
Irrigation is used in areas of low rainfall and is particularly valuable at the time of tasselling and fertilisation. Irrigation is necessary for production of green maize.
Maize usually responds well to fertilizers, provided other growth factors are adequate. Improved varieties can only reach their high yield potential when supplied with sufficient nutrients.
A maize crop of 2 t/ha grains and five t/ha stover removes about 60 kg N, 10 kg P2O5 and 70 kg K2O from the soil. Nitrogen6 uptake is slow during the first month after planting, but increases to a maximum during ear formation and tasselling.
Maize has a high demand for nitrogen, which is often the limiting nutrient. High nitrogen levels should be applied in three doses, the first at planting, the second when the crop is about 50 cm tall, and the third at silking.
Many soils provide substantial amounts of the phosphorus (P2O5) and potassium (K2O) but this is not adequate enough, especially at the seedling stage. Apply P2O5 near the seed for early seedling vigor. K2O is taken up in large quantities but plants’ requirement can usually be estimated by soil analysis.
K2O deficiency results in leaves with burnt edges and yellow or light green colour and empty cob ends, while P2O5 deficiency results in purple tinged leaves and hollow grains.
Nitrogen deficiency shows as yellow or light green stunted plants.
Phosphate is not taken up easily by maize and, moreover, some tropical soils are deficient in available phosphate.
Zinc deficiency symptoms include shortening of internodes and light streaking of leaves followed by a broad stripe of bleached tissue on each side of the leaf midrib. Occasionally the leaf edges and interior of the stalk at the nodes appear purple.
It is advisable to apply organic manures to improve soil structure and supply nutrients, all before8 ploughing. Nitrogen (N) can be applied in organic farming via green manure (legumes fixing N directly from the atmosphere), farmyard manure (FYM) or compost. Phosphorus can be supplied through FYM, compost, and in the form of rock phosphate (available in East Africa as Mijingu rock phosphate). Rock phosphate should be applied in the rows or planting holes at planting to promote root formation. Potassium can be supplied through FYM, compost and ashes. However, fertilizer recommendations based on soil analysis provide the very best chance of getting the right amount of fertilizer without over or under fertilizing. Ask for assistance from a local agriculturist office.
In rain-fed maize growing areas, plant seeds along with the first rain. This will allow roots to absorb the natural nitrates formed with bacterial action in the soil. Roots are susceptible to poor drainage, which causes stunted and yellowing of leaves. Stagnant water results to loss in N through leaching and denitrification (FADINAP, 2000).
In Africa maize does well when intercropped with beans or other legumes. The intercropped legumes should be sown at the time of first weeding in order not to crowd out the young maize plants. Since maize is a heavy feeder and takes considerable nutrients out of the soil, it can only be grown continuously on the richest soils or when heavily fertilized. Recommended legumes for intercropping in Kenya are: Beans , pigeon peas, cowpeas, groundnuts and Soybeans.
· Other crops that have been tried with varying success include
· Potatoes, Cassava, Pumpkin.
Intercropping maize with beans and other legumes regulates pests (leafhopper, leaf beetles, stalk borer, and fall armyworm) and increases the land utility. Intercropping Canavalia (Canavalia spp.) with maize improves soil productivity.
Intercropping maize with beans and squash enhances parasitism of caterpillars. This practice increases food sources for beneficial insects whereby increasing abundance of natural enemies. The intercropping system of maize-beans-squash is a low input and high yield strategy in the tropics. Maize yield is increased by as much as 50% over monoculture yield. Although the yields for beans and squash are reduced, the overall yield for the 3 combined crops is greater than when grown separately in monocultures (Agroecology Research Group, 1996).
Push-pull Desmodium (Desmodium uncinatum) and molasses grass (Melinis minutifolia) when planted in between maize rows keep the stem borer moths away. These plants produce chemicals that repel stem borer moths. In addition desmodium suppresses the parasitic witch-weed Striga hermonthica.
Napier grass (Pennisetum purpureum) and Sudan grass (Sorghum vulgare Sudanese) are good trap crops for stem borers. Napier grass has its own defense mechanism against crop borers by producing a gum-like-substance inside its stem, this prevents larva from feeding and causing damage to the plant. Both grasses attract stem-borer predators such as ants, earwigs, and spiders. Sudan grass also increases the efficiency of natural enemies, in particular parasitic wasps, when planted as border crops (Herren; Pickett, 2000; ICIPE, 2006).
Alternative uses of maize in mixed cropping
Shading of vegetable crops by planting single rows between vegetables in areas of high intensity of sunshine can increase yields of intercropped vegetables.
Use as support for runner beans for export or local consumption.
Maize can be harvested by hand or by special maize combine harvesters.
The stage of maturity can be determined by yellowing of the leaves, yellow dry papery husks, and hard grains with a glossy surface.
Maize is often left in the field until the moisture content of the grain has fallen to 15-20%, though this can lead to attack by grain borers in the covered cobs. In hand harvesting the cobs should be broken off with as little attached stalk as possible. They may be harvested with the husks still attached. These may be turned back and the cobs tied together and hung up to dry.
The world average yield in 2000 was 4255 kg per hectare. Average yield in the USA was 8600 kg per hectare, while in sub-Saharan Africa it was 1316 kg per hectare. Average yields in Kenya 2001-2005 ranged from 15-19 bags/ha (1350-1750 kg/ha) (Economic Review of Agriculture 2006).
15The major problems in most maize-producing areas are reducing the moisture content of the grain to below 13%, protection from insects and rodents, and proper storage after harvest. High moisture content with high temperatures can cause considerable damage such as development of aflatoxin producing fungi, making the product unsuitable for human and animal consumption.
Maize for home consumption is either sun-dried on the cob for several days by hanging up tied husks, or put in a well-ventilated store or crib.
Easy test for moisture content: take a few grains and try to crush them with your teeth – below 13% moisture level the grains are extremely hard and almost impossible to crush this way.
Shelling (the removal of grains from the cob) is usually carried out by hand, though several hand and pedal-powered mechanical shellers are now available. The average recovery is about 75%. The shelled grain is dried again for a few days and then stored in bags, tins or baskets.
The optimum moisture content for storage is 12-13%. Traditionally, the selected cobs are stored at home in the husk above the fireplace to prevent losses by insects. This is a common practice with small-scale farmers
Crop residues are removed from the field and then used as fodder, fuel, etc.
Infestation and damage by pests have been ranked as the third most important constraint upon maize production in semi-arid eastern Kenya after moisture stress and poor soil fertility (Songa et al., 2002).
Stem borers and striga weed account for losses in maize in the eastern and southern Africa region of 15-40% and 20-100%, respectively. When they occur together, farmers can lose their entire crop (ICIPE, 2006). Earworms and armyworms are other major pests.The principal pests of stored maize are Angoumois grain moth (Sitotroga cerealella), the larger grain borer (Prostephanus truncatus), maize weevils and rodents.
a. Field pests
They can damage maize from the seedling stage to maturity. The presence of small, faint yellow blotches on the lower
leaves is an indication of spider mite injury. As the colonies of mites increase in size they cause the lower leaves to become dry. The mites then migrate to the upper leaves. In Africa several species of spider mites have been reported on maize (mainly Tetranychus spp. and Olygonichus spp.). In Kenya, they are occasionally found on maize, but usually they are not of economic importance. 16
Provide good growing conditions for the crop.
Conserve natural enemies. Predatory mites and anthocorid bugs usually control spider mites.
The maize leafhoppers
The adults are about 3 mm long, slender and cream to pale yellow green in colour. These leafhoppers have two small black
spots between the eyes and brown marks behind the eyes extending along the body. They have brown lines along the wings. They usually hop away when disturbed hence the name. 17
The direct damage cause by maize leafhoppers by sucking plants is insignificant, but the indirect damage is high because they transmit the maize streak virus, a major disease of maize. Cicadulina mbila is the most important vector.
Plant maize well away from grassland or previously irrigated cereals; in particular, avoid planting downwind of such areas. The numbers of leafhoppers generally increase in irrigated cereals and grasslands – or in wild grasses during rainy seasons. Leafhoppers disperse away from these areas when dry.
Plant early – and if possible planting in an area should be carried out at the same time. Staggered planting of crops will favour multiplication of leafhoppers and increase the risk of virus transmission to later plantings.
Keep the fields free from weeds, in particular grasses.
Leave a barrier of 10 m of bare ground between maize fields and previously infested crops. This is reported to reduce virus incidence, by restraining movement of leafhoppers.
Remove residues of cereal crops since they serve as infection sources.
Use resistant varieties where available.
They are attracted to bright green surfaces, so can be caught in sticky green traps (see picture).
African bollworm (Helicoverpa armigera)
Caterpillars of the African bollworm also known as the corn worm or earworm attack mainly the developing cobs, although they may occasionally feed in the leaf whorl or on tender tassels.
Eggs are laid on the silks. Caterpillars invade the cobs and feed on developing grain. Development of secondary infections is common. Local outbreaks of this pest are sometimes severe.
Conserve natural enemies. Parasitic wasps, ants and predatory bugs are important in natural control of the African bollworm.
Monitor the crop regularly.
Use bio-pesticides. Plant extracts (e.g. neem, garlic, chilli,) and Bt are reportedly effective against the African bollworms. However, timing of application is very important. Spraying when caterpillars are inside the cob would be ineffective.
Handpick and destroy pod borers. This helps when their numbers are low and in small fields.
White grubs are the larvae of scarab “chafer” beetles. They are white, C-shaped with a brown head and 3 pair of legs.
Some species of white grubs (e.g. Phyllophaga spp, Heteronychus spp.) feed on roots of maize plants. Root damage is manifested by wilting seedlings, poor stands, and patches of tilted or lodged plants showing uneven growth. Injured plants can easily be pulled out of the ground.
Feeding of adults on maize leaves is usually not of economic importance. However, adults of the black maize beetles (Heteronychus spp.) are reported as major pests of cereals in many parts of Africa. They eat the stems of young shoots just below the ground. One adult beetle may destroy several seedlings in a row.
Remove old plants and weeds before planting.
Plough and harrow the field to expose eggs and grubs to predators (e.g. ants and birds) and to desiccation by the sun. Once exposed, they can also be picked by hand. This is feasible in small plots.
Provide conditions for growing healthy plants. They can tolerate grub feeding without serious damage.
Ensure proper drainage. Grubs love moist soil, especially with decaying organic matter. Female beetles prefer to lay eggs on moist-decaying organic matter.
Avoid planting maize immediately after old pasture in areas where grubs are frequently seen.
Observe a good crop rotation progaramme. In particular, in fields where white grubs are common.
Use trap crops and / or repellent plants. Good trap crops are African marigold, sunflower, and castor. Repellents plants are chives, garlic, tansy, and catnip. The crops trap and repel adult beetles from attacking the main crop grown (Golden Harvest Organics, 2003).
Cutworms (Agrotis spp. and other species)
Cutworms cut maize seedlings at or a little below ground level, make small holes along the initial leaves, or remove sections
from the leaf margins.
Eliminate weeds early, at least 2 weeks before transplanting.
Plough and harrow the field prior to transplanting. This exposes cutworms to natural enemies and desiccation and helps destroy plant residue that could harbour cutworms.
Make barriers to protect the transplanted seedlings. Barriers can be made by wrapping paper, aluminium foil and thin cardboard or similar materials around the base of transplant stems. Toilet rolls are handy as cutworm collars since they are readily available and will biodegrade into the soil.
Dig near damaged seedlings and destroy cutworms.
Conserve natural enemies. Parasitic wasps and ants are important in natural control of cutworms. Some maize varieties show partial resistance, such as “Katumani” in Kenya.
Examples are weaver-bird among many other grain birds
b. Storage pests
A number of beetles feed on dry maize causing post-harvest losses.
The most common are:
· Dinoderus sp., · Carpophilus sp., the coffee bean weevil (Araecerus fasciculatus), the lesser grain borer (Rhizopertha dominica), and the larger grain borer (Prostephanus truncatus).
The Infestation by these insects is heavier in the rainy season than in the dry season, is more prevalent in the humid zone than in the savannah, and is found more in large chips than in smaller ones. Pests’ invasion will be observed after a storage period of about 6-8 months.