Improving crop husbandry of maize

Organic maize management begins by selecting suitable varieties and using high quality seeds. Crop management focuses on creating growing conditions that keep the maize plants healthy.

Many small-holder farmers in sub-Saharan Africa grow traditional maize varieties. Seeds are collected from the farmer’s previous crop. These varieties have been developed based on specific farmers’ criteria and have become, over the years, adapted to local growing conditions. Besides being well-adapted to local conditions, such varieties are adapted to low nutrient levels and farmer cooking habits. They may also withstand local pest and disease pressures well. In addition, traditional varieties are locally available and farmers can reproduce their own seeds for replanting. Nevertheless, yields of traditional varieties are generally low to moderate due to the poor methods of selecting seeds and to poor management.

Besides traditional varieties, there are several improved open-pollinated and hybrid varieties of maize on the market in most places. They differ from one another with regard to characteristics such as yield potential, the time they take to reach maturity and their adaptability to specific growing conditions like drought, pests or diseases. Hybrids are generally higher yielding than open-pollinated varieties, if grown under suitable conditions. However, hybrid varieties are expensive because new seeds need to be bought for every planting season. On the other hand, improved open-pollinated varieties are often higher-yielding than traditional varieties and farmers can produce their own seed of open-pollinated maize varieties, thus reducing the costs for purchasing improved commercial varieties.

Another aspect farmers need to consider is the higher nutrient requirements of improved varieties. Most improved varieties will only perform well under improved soil fertility management conditions, for example after applying organic manure or using green manures.

In sub-Saharan Africa, land preparation for maize cultivation is dependent on the type of vegetation, but generally, field preparation is done using simple implements. In the forest regions where there are shrubs, a cutlass is used to slash the shrubs. However, in the savannah region, farmers instead use a hand hoe or animal traction with oxen. For organic maize production, it is recommended to minimize or reduce soil disturbance during the land preparation. Full tillage is thus restricted to situations where noxious weeds such as spear grass (Imperata cylindrica) or couch grass (Digitaria scalarum) must be removed.

Under zero tillage, a dense legume cover crop, for example lablab (Lablab purpureus), velvet bean (Mucuna prurenis) or sunhemp (Crotalaria juncea) should be planted to suppress weeds and should only be cleared at the time of planting. The cover crop is cleared by slashing and strong weeds are pulled or dug out. Apart from suppressing these weeds, the legumes contribute to soil fertility when incorporated into the soil. Planting rows are then made directly using a hoe, oxen or tractor without ploughing the land in order to minimize moisture and organic matter loss. A short legume cover crop like beans, peas, soybean or mung beans is later planted as an intercrop at first weeding to cover the soil while the maize grows.

• Count 100 seeds of the selected maize variety and put the seeds between moist newspaper sheets, keeping them moist. Place the paper with the seeds in a safe area where children or animals will not disturb it. 
• After four days of incubation, count the number of seeds that have germinated and express it as a percentage. For example, if out of the 100 seeds 85 seeds germinated, germination percentage is 85.

A germination percentage of between 85 and 100 is considered good for the maize crop. In case germination rate is lower, you may increase sowing density correspondingly to ensure appropriate plant density.

Generally, African small-scale farmers plant maize seeds by hand (dibbling) or using oxen-drawn planters, while a few large farms use tractor-drawn planters. Planting should preferably be done at the start of the rainy season to enable good seed germination and proper plant establishment. Delayed planting in relation to the onset of rains will affect yields, as the young plants will not receive enough rain for proper growth and development.

Usually, maize is sown in rows at a recommended spacing of 75 to 90 cm between rows and 25 to 50 cm within the row, with a seed rate of 2 seeds per hole. Where maize is to be intercropped with a legume, the legume should be planted in rows midway between maize rows.

The appropriate planting depth varies from 2 to 10 cm, depending on the weather conditions and the moisture status of the field. For example, in areas with adequate rainfall and well-drained sandy-loam soils, planting depth of 2 to 3 cm is optimal, as deep seed placement retards germination and emergence of maize seedlings. In dry areas where the soil is dry and sandy, maize seed may be planted more deeply (5 to 10 cm). This enables the development of a deep root system to obtain the needed water and nutrients. Deep roots penetrate far into the soil and use moisture and nutrients from the deeper depths of the soil.

Intercropping helps to reduce the risk associated with the failure of a particular crop and reduces the risk of pest and disease attacks and shocks from drought. If one of the crops in a multiple cropped field is damaged, it is likely that the other crop can compensate for yield losses. This is partially due to the fact that the different crops use different growth resources in the environment and have different growth habits. Moreover, intercropping contributes to a more varied and balanced human diet and improves soil.

In sub-Saharan Africa, maize is commonly intercropped with beans or other legumes as well as with other food crops such as cassava and pumpkin.

Intercropping of maize and legumes such as common beans, ground nuts or cow peas is a common practice in most small-scale farming systems in sub-Saharan Africa. Both crops are normally sown at the same time in the field in separate rows. Later on, the maize stems may serve as stakes for the climbing beans. In addition, other crops such as cassava may be grown.

Intercropping of maize and pigeon pea is common in Malawi, Eastern Zambia and Northern Mozambique. Research has shown that in the long term, pigeon pea is one of the legumes with the highest positive effects on soil fertility and maize yields. Even though early growth of the pigeon pea is reduced when intercropped with maize, the pigeon peas compensate by continuing to grow after the maize is harvested. The pigeon pea also provides large quantities of biomass, and the seed is harvested for food. Due to its attraction to livestock, pigeon pea needs to be protected from grazing animals.

Different types of dense covering legumes can be intercropped with maize. They are sown at the same time as the maize and when they cover the ground, they are then cut and left as mulch cover. Sunhemp (Crotalaria juncea) has been successfully used in Zimbabwe for green manuring and as an intercrop with maize. Other dense legume covering crops such as lablab (Lablab purpureus) and velvet bean (Mucuna pruriens) are also commonly used.

Repeated planting of maize in the same field year after year leads to a decrease in the available nutrients necessary for plant growth and lowers yields. To avoid this, farmers should grow maize in rotation with legumes like groundnut, cowpea, pigeon peas and soybeans. Planting maize after a legume in rotation improves soil fertility and results in higher yields. In addition to fixation of nitrogen from the air, legumes interrupt the multiplication cycles of cereal diseases, provide food for humans and feed for animals and produce considerable amounts of organic materials that can be incorporated into the soil. Legumes are also known to solubilise phosphorus that is bound in the soil, and substantially increase microbial activity in the soil.

Growing green manure crops like cowpea, velvet beans or crotalaria can also generate sufficient nitrogen for a following maize crop. However, in many systems, cowpea has proved to have the shortest growing period providing sufficient nitrogen in only 8 to 10 weeks of growth.

Traditionally, farmers would restore soil fertility after a period of cultivation by leaving part of their land uncultivated for up to 5 years in order for fertility to buildup, while new and more fertile land is cultivated for food production. The increasing population density has reduced the amount of land available to the farmers, and forced many farmers to shorten the fallow period or even to abandon the fallowing practice entirely in some areas. A natural short fallowing of overworked land will result in little or no improvement in soil fertility. It is therefore important to improve fallowing systems.

Experience has shown that the inclusion of improved short duration fallows of 1 to 3 years in rotations is important for significant improvement in soil fertility. Multi-purpose trees can be used to improve fallows. For example in Zambia, improved fallows using Sesbania (Sesbania sesban) have been found to be a good way of adding significant amounts of nitrogen and organic matter to soil. Green manure cover crops can also be used. For example in West and East Africa, maize is grown after a short lablab fallow to improve the productivity of maize, where lablab is incorporated into the soil before maize is planted. By planting lablab as green manure crop, soils are protected against erosion, nitrogen is fixed and weed infestation is controlled. As a result, soil fertility is significantly improved and the productivity of subsequent maize enhanced. For this purpose, it is recommended to establish improved fallows by planting different fallow species, as they make plant nutrients available for a longer period.

Although the content of essential nutrients in maize stovers is relatively low compared to that in the grain, stover can contribute to soil improvement. It is therefore important to avoid burning or removing maize stovers and other crop residues from the field. The practice of burning crop residues is also not allowed in organic farming. Organic farmers leave crop residues on the land as mulch to decompose and return their constituent nutrients.

The integration of farm animals can contribute to better recycling of nutrients within the farm if the animals are fed farm-own forage legumes, maize residues and the manure is returned to the field. Maize plants will benefit from the valuable manure from cattle, sheep, goats, pigs or chickens, especially when it is collected and composted with kitchen remains and crop residues.

Efficient use of rainwater can be enhanced through the following practices:

• Adopting minimum or zero tillage practices to minimize the exposure of soil to water loss.
• Planting suitable varieties for the local conditions. Early maturing varieties are preferred for short rain season areas.
• Early planting at the start of the rains to ensure that the plants get enough moisture, especially around flowering.
• Proper weed control to reduce competition for water.
• Using organic materials such as compost, mulch and organic manures to improve the soil’s capacity to absorb and store rainwater.
• Mulching with crop residues from previous harvest can be used as trashlines to reduce evaporation losses.
• Reducing maize plant population is an important consideration in arid areas where irrigation is not available to increase the amount of water and nutrients available for each plant.
• Water harvesting structures, for example, by diverting runoff from other areas (uphill or road runoff) onto a field. However, given the fact that maize does not tolerate waterlogging, water should not be allowed to stand in the maize field.

Maize is one of the most efficient grain crops in terms of water utilization, and thus can produce very high yields under irrigation. However, most maize production in sub-Saharan Africa is rainfed. Occasionally maize is grown under irrigation in areas with warm and dry periods (e.g. semi-arid areas) to ameliorate the effects of drought. In peri-urban areas, where maize is normally grown for the fresh market, irrigation is used for out-of season production.

Experience has shown that the most appropriate and suitable irrigation scheme for small-scale farmers is the drip system. In drip irrigation, water is applied only to the soil around the maize roots, so that they can easily access the water. This means less water is needed and the water is efficiently used.

• When irrigation water is limited, irrigation scheduling should be based on ensuring the maize plants have enough water not to dry out during flowering. Drought stress during this period reduces yields considerably.
• Irrigation will reach higher efficiency only if it is combined with good measures for improving the soil structure and water retention of the soil.

Successful weed management in maize is best achieved by using a combination of measures including:

• Prevention of introduction and spread of weed seeds, for example by using clean seeds and equipment.
• Improved fallowing by using a dense covering legume that covers the soil well, such as lablab or mucuna, will suppress weed growth thus reducing its multiplication. This should be alternated with a cover crop within the maize crop in order to completely suppress the weed. 
• Manual or mechanical weeding to remove the weeds is also necessary. This is because maize is greatly affected by weeds during the first 10 weeks of growth.

Bt-maize is genetically engineered to make it resistant to the stem borer. It is created by adding the genes from the soil bacterium Bacillus thuringiensis to the maize seeds. It produces a toxin that kills the stem borer. Bt-maize has been cultivated in some countries including South Africa and Kenya, mainly among large-scale farmers because of the high price of seeds. Apart from being expensive for small-scale farmers, farmers are not allowed to save or exchange seed of Bt-maize. Moreover, there is evidence that stem borers quickly develop resistance to Bt-maize and some fear that the pollen could transmit the Bt-gene to local maize varieties.

The most common storage pests of maize are the Angoumois grain moth (Sitotroga cerealella), the larger grain borer (Prostephanus truncatus), grain weevils (Sitophilus spp.) and rodents (mostly mice). They can be managed by a combination of measures:

• Early harvest of the maize to prevent or reduce infestation of the maize cobs in the field.
• Growing suitable varieties that have the husk covering all of the grains.
• Proper drying of the maize grain is an important procedure in storage pest prevention. In order to be stored safely, the produce must be dried quickly after harvest and only be stored after it has been thoroughly dried.
• Good hygiene in the storage area by cleaning out all residual pockets of infestation at the end of the storage season minimizes reinfestation of the new harvest. Removing all dark corners, sealing off all potential entry points and clearing the surrounding spots where rodents are likely to hide, is helpful to control rodents.
• Periodic inspection and removal of all infested maize cobs or grain.
• Use of plant extracts, for example, crushed, ripe, dry chilli pepper pods and mixed with wood ashes, and mixed with dried maize ready for storage to repel and kill maize weevils.
• Use of natural enemies, for example, the predatory beetle Teretrius nigrensis has been used in many African countries in an attempt to control the larger grain borer.