Sorghum crop should be harvested as soon as the grain in the ear head attains the colour of grain and the grain hardens. At this stage, the grain will contain 15-20 per cent moisture. Complete uniform maturity may not be possible in sorghum. In most cultivars, stalks and leaves are still green and succulent when the grain is already mature.
It is rarely practical to delay harvest until the moisture content of the grain has dropped to a level enabling storage without prior drying. Losses due to lodging, shattering and bird damage will make the procedure more costly than the additional handling of grain involved in earlier harvest.
In India, grain sorghums are harvested by cutting of the heads with a sickle. The standing stalks, depending on the convenience, will be cut at ground level for feeding the cattle. In certain areas, the plants with ear heads are cut at ground level and the heads are then separated from stalks in a day or two, depending on the convenience.
Harvested ear heads are dried in sun for a day or two or until the grain moisture content drops to around 12 per cent. Traditionally, threshing of sorghum is accomplished by tampering under the feet of cattle, by running stonerollers over the dried ear heads or by beating with sticks.
Increasingly, locally manufactured power operated threshers are being employed and several small-scale grain threshers have now been developed. The threshed grain has to be cleaned and dried to 12 per cent moisture content for safe storage. The seed is usually sun dried in thin layers after cleaning by winnowing.
Storage:
Sorghum grain is stored to prevent physical losses and to maintain grain quality during storage period. Loss of quality may be due to moulds, insects and rodents. Moulds on sorghum grain are capable of producing aflatoxin. A number of simple storage techniques are used for storing the grain.
Dried earth granaries, granaries made with plant material, underground stores and earthen or metallic containers are commonly used for small-scale storage. Storage of grain in jute sacks inside storehouses is a satisfactory method. Sacks should be kept away from direct contact with walls and floor. In more advanced areas, grain is stored in concrete silos.
Insect pests pose a threat to safe keeping of sorghum grain. Important storage pest is rice weevil. Mould development may not be a problem if the grain is dried to less than 12 per cent moisture content before storage and humid air does not enter the storage structures, especially during rainy season. Traditional methods of storage may be satisfactory if the quantity is small and the storage period is less than a year.
These methods include mixing the seed with ash, sand or dried neem leaf. Sophisticated storage methods use contact insecticide sprays or dusts to surfaces in empty storage structure before storing the grain. After storage, the stores are usually disinfested by fumigation. Methyl bromide 16 g m-3 for 12 hrs or Phostoxin 3 g tablets (one or two) t-1 of grain for about five days can keep away the storage pest in safety limits.