AgriGuide

Maize

Maize (Zea mays L.) is a major staple food in sub-Saharan Africa. It can be used as food and animal feeding, as well as a source of industrial raw material. In sub-Saharan Africa, maize is grown mostly by small-scale farmers under rainfed conditions mainly for human consumption. It is consumed as green maize fresh on the cob, or is baked, boiled or roasted.

Low yields in sub-Saharan Africa can be attributed to a variety of factors:

• Poor soil fertility as one of the leading challenges for small-scale farmers. The increasing population density resulted in land exploit intensification and forced farmers to shorten or abandon the previously well followed fallow periods. As a result, nutrients and organic matter in the soil have become heavily depleted and this has resulted in reduced soil fertility and productivity.
• The use of low quality seeds. Poor seed selection and limited use of new improved commercial varieties are among the reasons farmers are not able to cope with the productivity demand.
• Unsuitable crop husbandry practices such as late planting, poor weed management, pest and disease attacks (stem borers) and the Striga weed are important constraints that lower maize yields. High post-harvest losses especially due to improper drying and storage, lead to moulding and attack by the maize weevil during storage.

• Soil moisture stress is a continuous problem for many farmers who continue cultivating maize under rainfed conditions. The erratic nature of rainfall, including distribution leads maize to severe soil moisture stress; reducing yields significantly.

Selection of suitable varieties

The choice of appropriate maize varieties for a given location is important, as it makes a significant contribution to yield improvement. Furthermore, farmers must also consider the differences between modern varieties and traditional varieties. Wrong variety selection can lead to a poor harvest or total crop failure. Therefore, it is important to carefully select varieties that match with local growing conditions; including climatic conditions, nutrient level of the farm as well as cooking habits and dietary requirements of the consumers.

Traditional varieties as landraces

Small-holder farmers in sub-Saharan Africa grow traditional maize varieties. Seeds are collected from the farmer’s previous crop (recycling). These varieties have been developed based on specific farmers’ criteria and have become, over the years, adapted to local growing conditions (landraces). Besides being well-adapted to local conditions, such varieties are adapted to low nutrient levels and farmer cooking habits. Seed may also withstand local pest and disease pressures well. 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.

Improved varieties

Besides traditional varieties, there are several improved open-pollinated and hybrid varieties of maize in most local markets. They differ from one another with regard to characteristics such as yield potential, growth period and their adaptability to specific growing conditions like drought, pests or diseases. Hybrids are 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, therefore reducing costs for purchasing improved commercial varieties.

Recommendations of on-farm multiplication of maize seeds

Farmers can produce and multiply on-farm seeds from open-pollinated maize varieties. The following recommendations are meant to guide farmers in seed production:

• Select a suitable open-pollinated variety for the agro-ecological zone. This can be sourced from the existing preferred maize crop on the farm, neighbours, the national maize program or a local seed company.
• Choose the best plot and weed it. Maintain a distance of at least 300mt from any nearby maize crop of a different variety. This would avoid cross-pollination between varieties and maintain the characteristics of the preferred variety. Alternatively, farmers can sow the preferred variety one month earlier or later than neighbouring maize fields.
• Plant maize seed crop early and carefully. Examine and manage the maize plants as they grow to ensure a healthy growth and development.
• Select healthy looking maize plants, particularly those not infected with diseases or attacked by pests. The selected plants should have cobs of good size with well filled seeds. Label the cobs in the field and let them mature properly.
• Harvest the cobs when the plants start to dry, but making sure cobs do not get mixed with cobs from other maize varieties. Allowing the cobs to over-dry will predispose them to infestation by weevils on the field.
• Dry the cobs further with their sheath cover, on a clean and dry surface in the sun.
• Remove the sheath cover and shell the dried cobs, being careful not to damage the seeds by taking the best seeds, which come from the middle of the cob. After shelling, dry the seeds further; well dried seeds crack when bitten. Clean the seed by removing all dirt and foreign matter, and small and damaged seeds. Pack the seeds in a sack to stand on pallets in a clean, dry and well-ventilated store. Maintain a distance of about 0.5mt away from the wall of the room.

Improved fallowing

Traditionally, farmers would restore soil fertility after a period of cultivation by leaving part of their land uncultivated for up to 5 years for fertility to restore, while new and more fertile land is cultivated for food production. However, the increasing population density has drastically reduced the amount of land available for farming, forcing farmers to shorten the fallow period or even to abandon the fallowing practice entirely. 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, 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. Soil fertility is improved and the productivity of following maize enhanced. It is recommended to establish improved fallows by planting different fallow species, as they make plant nutrients available for a longer period.

Weed management

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

• Prevention of introduction and spread of weed seeds, 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 to completely suppress the weed.
• Manual weeding to remove the weeds is also necessary. Maize is greatly affected by weeds during the first 10 weeks of growth.

Management of Striga weed

Two species of Striga are found in sub-Saharan Africa: Striga hermonhica in West and Central Africa, and Striga asiatica in Eastern and Southern Africa.

Striga is a parasitic weed that only grows by attaching itself to roots of a host plant like maize. Striga sucks nutrients from maize plants, leading them to be smaller and weaker. The attack brings to yield losses or even complete crop failure. Once Striga becomes well established on the ground it is difficult to control it, partly due to its high reproductive capacity. Striga also produces thousands of seeds, which can survive in the soil for several seasons and germinate only when a cereal crop is planted. Successful Striga management is achieved by using a combination of measures, also used for weed management, as follows:

• Prevention of Striga introduction and spread of weed seeds. Use clean seeds and equipment as well as Striga resistant or tolerant maize varieties, in case they are available;
• Legumes that are grown in rotation or intercropping with maize stimulate the germination of Striga, but inhibit post-germination growth of the weed because it cannot grow on the roots of legume crops. It is recommended to plant green manure and fodder crops such as desmodium, sesbania, crotalaria or fodder grasses like Napier grass, for at least two seasons, and to plant maize or cereals only once every two to three seasons until all Striga is eliminated.
• Intercropping maize with desmodium or other legumes such as mucuna between rows of maize has been shown to improve soil fertility and significantly suppress Striga weeds.
• Farmers can also regularly walk through their fields and uproot any growing Striga plants. However, this should be done early enough before the Striga produces seeds, and before it greatly affects the maize.

Reducing post-harvest losses

Timely harvesting

Maize is harvested by hand on the cob in small-holder maize farming. Maize that is to be eaten green is ready for harvest when the grain hardens or when the silky flowering at the top of the cob turns black. At this full maturity stage the crop has a moisture content of about 30%. However, maize to be dried is left to partly dry in the field until all the leaves of the plants have turned brown. This bears the considerable risk of the grains spoiling by feeding birds. Many small-scale farmers wait too long to start harvesting because they lack suitable drying facilities.

Delayed harvesting can lead to rotting of the cobs, attacks by rodents, birds and weevils. It also allows fungal pathogens such as aflatoxins to spread, especially if the drying crop is rained on while still in the field. At harvest, the husks are removed from the cobs.

Drying

Quickly after harvest, the cobs should be dried under the sun before being shelled. If the grains are not well-dried, they will attract insect pests and mildew. To test whether the grains are dry enough, shake a handful of grains and half a handful of salt in a dry soda bottle for 2 or 3 minutes. If after the grains are allowed to settle, the salt sticks on the walls of the bottle, this means the grains still contain moisture. Grains should be dried again and tested repeatedly until no salt sticks to the bottle before being stored.

Drying should not be carried out on the bare ground, but on a cemented floor, on mats or tarpaulins on a raised structure like cribs or specially constructed drying sheds. This is to avoid the grains picking up moisture, dirt and insects. In case of open air drying, the grain should be protected from rain, night dew, domestic animals and birds.

Storage

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 where the husk covers all of the grains.
• Proper drying of the maize grain is an important procedure in storage pest prevention. For maize to be stored safely, it must be dried quickly after harvest.
• Minimize re-infestation of the new harvest by cleaning out all residual pockets of infestation at the end of the storage season.
• Removing all dark corners, sealing off all potential entry points and clearing the surrounding spots where rodents are likely to hide.
• Periodic inspection and removal of all infested maize cobs or grain.
• To repel and kill maize weevils, use plant extracts, for example, crushed ripe, dry chilli pepper pods mixed with wood ashes, and with dried maize ready for storage.
• 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.

Bt-maize is genetically engineered to resist stem borer. It has been created by adding the genes from the soil bacterium Bacillus thuringiensis to the maize seeds. Bt-maize produces a toxin that kills the African white stem borer (Maliarpha separatella (Ragonot). Apart from being expensive, farmers are not allowed to save or exchange Bt-maize seed. Stem borers quickly develop resistance to Bt-maize and pollen could transmit the Bt-gene to local maize varieties.

After drying, maize should be stored in a clean and well-ventilated storage area, separating old from new grain stocks. There are different ways of storing maize.

• Maize is stored by hanging cobs, before shelling, on kitchen fire rafters to prevent insect damage. It is recommended to shell cobs immediately after drying to reduce weevil damage;
• Shelling of the grains should be done carefully, so that the grains do not get damaged. After shelling, the grains should be cleaned by removing any dirt and foreign matter, small and damaged seeds;
• Cleaned shelled grains are stored in small household storage metallic silos or packed in sacks (bags with perforations) and stored well on pallets in clean and well ventilated stores. Under such conditions, grain can be stored up to two years without significant reduction in terms of quantity and quality.

Farmers who do not have adequate storage capacity are advised to sell off the grain immediately to avoid incurring losses. Well-dried and shelled grain is ready for milling into flour and further processing into other products.

Marketing and organic certification

The majority of maize produced in Africa is consumed locally. Maize has also become a cash crop with local industries such as for the livestock sector and breweries, due to economic growth, urbanization and rising incomes. There are growing domestic and continental market opportunities for maize throughout sub-Saharan Africa. Organic farmers can exploit this potential to position organic maize at the national and continental levels.

However, the market for certified organic maize is still very small, or does not exist. Many small-scale farmers are already using some organic practices such as intercropping. They can easily learn and make use of full organic practices to establish sustainable and productive production systems for their families and take advantage of the local market opportunities without organic certification.