Harvesting, Post-Harvest Handling and Storage
What you must understand
Know maturity indices: physiological maturity (black layer in maize), moisture content, days to maturity, colour change, and firmness. Understand harvest methods - hand, mechanical - and the importance of harvesting at the right moisture. Know moisture content and safe storage moisture: cereals generally around 12–13%, oilseeds lower. Understand drying: sun drying, artificial drying, and the risk of cracking grain with too-rapid drying.
Know storage losses: insects (weevils, grain borers), moulds (Aspergillus, aflatoxin risk in moist warm conditions), rodents, birds and moisture migration. Understand storage structures: cribs, silos, hermetic bags, metal silos, and the value of cleaning, drying, and treating grain before storage. Know threshing, winnowing, shelling, grading, packaging and transport. Understand the difference between quantitative loss (weight) and qualitative loss (quality, germination, market value).
Traps in questions
- Grain stored above safe moisture develops mould and aflatoxin, not just insects.
- Aflatoxin is a health hazard and a market rejection risk, not merely discolouration.
- Mixing new and old grain spreads infestation.
- Sun drying too fast on hot surfaces cracks grain and lowers grade.
- Harvesting too early reduces yield; too late causes shattering and lodging.
Rule of thumb
Dry, clean and cool: grain should be dry to safe moisture, free of chaff and broken grain, and stored cool and airtight where possible.
Worked example
A farmer harvests 2 000 kg of maize at 20% moisture and dries to 13%. Dry matter is 2 000 × 0.80 = 1 600 kg. At 13% moisture the final mass = 1 600 ÷ 0.87 ≈ 1 839 kg. The apparent 161 kg loss is mostly water, not grain - a common exam trap.