Crop Production and Management
Crop production questions test agronomic decisions from land preparation to storage, using Namibian staple and cash crops: pearl millet (mahangu), sorghum, maize, cowpea, groundnut, bambara nut and irrigated wheat or horticulture.
Core rules
- Plant at the onset of steady rain, not the first shower. Correct planting depth is roughly 3-5 cm, deeper on drier sands.
- Row planting makes weeding, fertilizer placement and plant counts possible. Weed during the first 3-6 weeks, the critical period for yield loss.
- Cereals need nitrogen, split between planting and top-dressing; legumes fix nitrogen but still need phosphorus and inoculant where appropriate.
- Rotate cereals with legumes to break pest and disease cycles and improve soil nitrogen.
- Harvest at physiological maturity and dry grain below about 12.5% moisture before storage. Store on pallets in a clean, dry store; hermetic bags or ash help control insects.
Pests and problems
- Quelea birds, armyworm and stalk borer attack cereals; Striga attacks sorghum and millet in poor soils.
- Continuous cereal cropping increases nematodes and soil-borne disease.
Worked example
A maize field is planted at 0.75 m between rows and 0.30 m within rows. Each station occupies 0.75 x 0.30 = 0.225 m2, giving 1/0.225 = 44 444 stations/ha. With one plant per station and a 1000-grain weight of 300 g, pure seed needed is 44 444/1000 x 0.3 kg = 13.3 kg/ha. At 90% germination, divide by 0.90 to get 14.8 kg/ha; add 5% for field losses, about 15.5 kg/ha. The reasoning links spacing to population, then population to seed mass and germination.
Traps
- Confusing seed rate with plant population.
- Forgetting germination percentage and field losses.
- Applying nitrogen to dry soil or at the wrong stage.
- Storing grain above safe moisture and losing the crop to mould.