Choosing a Field for Maize After a Dry Winter
A farmer near Mahalapye has two adjacent plots and must plant maize within three weeks, before the rains are expected. Plot A is a sandy loam on a gentle slope where the previous season's maize yielded well but the topsoil now crusts hard and shows pale grey patches; a soil test shows pH 4.9, low organic matter and very low phosphorus. Plot B is a heavier clay loam in a slight depression where water stood for several days last season; it tests pH 6.6 with moderate phosphorus but the farmer noticed yellowing and stunting of the previous sorghum crop in wet patches. The farmer has limited funds, can afford either 300 kg of lime or 200 kg of single superphosphate, but not both, and has one season of cattle manure available. Rains are expected to be below average.
1. Which plot should be planted to maize this season, and why?
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Plot A is the better choice, despite its poor fertility, because the key limiting factor this season is water. Plot B is a depression where water stood for days; with a below-average rainy season it may still waterlog after heavy storms, and waterlogging causes the yellowing and stunting already seen in sorghum (root oxygen starvation). Clay loam in a depression also dries and warms slowly, delaying planting. Plot A's sandy loam warms and drains faster and the previous maize yielded well there, showing the site can produce maize. Its problems (acidity, low phosphorus, low organic matter) are fertility constraints that can be managed, whereas Plot B's problem is a physical/water constraint that cannot be fixed within three weeks. Decision rule: match the crop to the field whose main limitation is correctable with the resources and time available.
2. Given the limited budget, how should the farmer spend it, and what should be done on the chosen plot before planting?
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Spend on correcting the most limiting nutrient on the chosen plot rather than on the other plot. On Plot A, phosphorus is very low and maize responds strongly to it at establishment, so the single superphosphate is the higher priority; but the pH of 4.9 also restricts nutrient availability. A defensible plan: apply the available cattle manure broadly to raise organic matter, buffer acidity and improve the crusting surface; band the single superphosphate at planting near the seed rather than broadcasting, to get maximum response from a small amount; and defer liming, since lime needs months to act and 300 kg spread over a field is too little to shift pH much. If the farmer can obtain a small amount of lime, apply it in the planting rows only. Do not spend on Plot B, which will not be planted.
3. The farmer asks whether to plant immediately after the first rain or wait. Advise, giving reasons.
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Advise waiting until the soil is wet to the depth of the seedbed (roughly 15–20 cm) and the risk of a false start has passed, rather than planting on the first light shower. On a crusting sandy loam with a dry subsoil, a small early rain wets only the surface; seed germinates and then dies when the subsoil remains dry, forcing replanting and wasting scarce seed. Waiting also allows the manure and phosphate to be worked in and the crust broken. The trade-off is that late planting shortens the growing season, so the farmer should set a cut-off date: if the rains have not come adequately by that date, switch to a shorter-maturing maize variety or a drought-tolerant crop such as sorghum or cowpea rather than plant maize late.