Minimising losses at harvest and in storage

Proper harvest and post-harvest handling of sorghum aims at minimising losses and maintaining grain quality. Timely harvest and adequate drying of the grains before storage considerably reduce storage losses. Cultivars with hard grain suffer less damage at storage.

Timely harvesting

Prompt harvesting of mature grains is important to avoid major losses, mainly those caused by birds. Rain-fed sorghum crops are harvested at the end of the rainy season when the grain has become hard. Most farmers in the tropics harvest sorghum manually by either cutting the heads or removing the whole plant. Where short cultivars are grown, the plants can be harvested mechanically using a combine harvester.

Sorghum grain yields under traditional farming practices in Africa are as low as 0.5 to 0.9 tons per hectare. If conditions are favourable and improved cultivars are used, yields of 3 tons and more per hectare are possible.

As a general rule, sorghum stalks and re-growth should be dug or ploughed into the soil, grazed or destroyed soon after harvest to prevent further development of insect pests. Burning of the residues is not recommended in organic farming, as it destroys valuable soil organic matter in the top soil and kills soil organisms. Sorghum forage is often dried and stacked along the field as trash lines or made into silage. Drying and ensilage of sorghum forage avoids animal poisoning from prussic acid. In case of pasture use, re-growth of sorghum plants is best, if stubbles with no less than 10 to 15 cm length are left. Forage sorghum is usually only cut once after flowering under rain-fed conditions. Under conditions of sufficient water and nutrients forage sorghums can be harvested multiple times.

In some areas with a climate that allows two subsequent crops of sorghum, ratooning of sorghum is common. The practice aims at getting more than one harvest from a single sowing. Immediately after the first harvest the plants are ratooned. Compared to a newly sown crop a ratoon crop develops faster because of its established root system which utilises the available water in the soil early in the season, matures earlier and therefore can avoid losses by migratory quelea birds. Ratooning also saves on labour for ploughing and planting. Where the parasitic Striga weed or soil borne pests and diseases prevail, two subsequent crops of sorghum are not recommended. To achieve good yields, the crop is thinned to 2-3 tillers per hill. Weeding and other management practices are done as for a newly sown crop.

Proper drying

Traditionally, the harvested panicles are properly dried in the sun for about 2 weeks. Drying is ideally done by spreading the grains on a mat or tarpaulin to minimise ground contamination and fencing-in the area to keep out domestic animals. Furthermore, grains should be protected from rain, as rain can delay drying and lead to the development of mould.

Threshing and winnowing

Threshing is done to separate the grains from the panicles. As in wheat, the seeds separate easily from the floral brackets when threshed. Traditionally, the dried panicles are filled in sacks and the sacks are hit gently with a stick to loosen the seeds off the panicles. With this method, care should be taken not to damage the seeds. After threshing, grains are winnowed to remove any foreign matter.

Proper storage

For storage, grains should be filled into bags made of jute or sisal that allow good aeration. This reduces infestation with storage pests and moulds. To further reduce infestation by fungi and insects, a layer of neem leaves can be laid out on the bottom of the granary. Rat-guards should be used to prevent entry of rats into the granaries. Stored grain can further be brought out periodically and exposed to the sun in order to reduce the build-up of high humidity conditions, which is a precursor for mould development. Attention should be paid not to use bags or containers which contain traces of pesticides or other chemical products, in order to avoid any contamination of the grains.