Late-Sown Wheat After Late Cotton: Variety, Seed Rate and a Waterlogged Patch
Ramkishan farms 1.6 ha of irrigated sandy loam near Hanumangarh. His cotton was picked late, so the field will be free only on 18 December. He already owns seed of a 145-day wheat variety; a 115-day variety is available in the market. Soil test reports 168 kg/ha available N, 22 kg/ha Olsen P and 310 kg/ha exchangeable K. He plans 100 kg seed/ha, 120 kg N, 60 kg P2O5 and 40 kg K2O, with four irrigations. The canal turn is fixed for 24 December; a tube well is available after that. Last year wheat sown on 5 December with the long-duration variety yielded 4.6 t/ha, while neighbouring late-sown fields yielded 3.2–3.5 t/ha. Night temperatures are 6–8°C and are expected to rise sharply after 15 March. Labour is scarce. The field slopes 0.3%, and the lower 0.3 ha has a history of waterlogging.
1. Advise on variety, sowing date, seed rate and seed treatment. Show how each choice is linked to the temperature and water constraints.
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Decision: buy the 115-day variety and target 22–24 December, not later. Use 125 kg seed/ha and treat the seed before sowing.
Reasoning
- The main risk is terminal heat, not cold. A 145-day variety sown on 24 December would reach grain filling after 15 March, exactly when temperatures rise sharply; a 115-day variety advances flowering and grain filling by about three weeks.
- Sowing should not wait for the 24 December canal turn if the tube well can provide a pre-sowing irrigation. A 3–5 day delay is less damaging than sowing dry and waiting for water.
- 100 kg/ha is a normal timely-sown rate. Late sowing reduces tillering, so raise the rate to about 125 kg/ha to establish more main shoots. Going above 130–140 kg/ha risks lodging, more disease and small ears; it is not a substitute for early sowing.
- Shallow sowing (about 5 cm) into moist soil is important; deep sowing in a late, warming seedbed reduces emergence.
- If sowing slips past the first week of January, do not force wheat. Switch to barley for grain or oats for fodder, which fit the shorter season better.
2. Redesign his fertilizer and irrigation schedule for the late-sown crop. State what you would change and what you would keep, with reasons.
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Keep the P plan, but change N timing and irrigation. Soil K is 310 kg/ha, which is high; 40 kg K2O is unlikely to pay. Reduce K to 20 kg K2O or omit it and put the saving into seed. Apply the full 60 kg P2O5 and half the N (60 kg N) basally. Apply the remaining N in two doses: at crown-root irrigation and at tillering. Do not reserve N for late booting; late N delays maturity and increases heat and lodging risk.
Irrigate first at 17–21 days after sowing, not at 28–30 days, because late-sown wheat reaches crown-root stage sooner. Then irrigate at tillering, flowering and milk. Keep the last irrigation light and stop well before harvest. On the lower end, cut a shallow drain and irrigate in small streams; do not let water stand for more than a few hours. Applying extra N to 'compensate' for late sowing is a mistake: it produces soft, late growth.
3. The lower 0.3 ha remains waterlogged. What would you do with that patch, and how does it change your overall plan and expected yield?
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Do not sow the 0.3 ha waterlogged patch to wheat. Wheat is sensitive to waterlogging at crown-root and jointing; a crop on that patch is likely to yield under 1.5 t/ha and may fail altogether. Put the patch under barley (more tolerant) or a fodder oat crop, and use it to carry the drain outlet for the rest of the field. Keep the wheat plan on the upper 1.3 ha. At a realistic 3.4–3.5 t/ha, that gives about 4.4–4.6 t of wheat, plus fodder from 0.3 ha. If the entire 1.6 ha were sown to wheat and the lower patch waterlogged, the expected crop would be lower and the risk of a poor, uneven harvest higher. The patch should also be levelled before the next season.