Sowing wheat on 8 December: seed lot, seed rate and water scheduling
Harpreet Singh farms 4 ha of canal-plus-tubewell irrigated land near Ludhiana. His paddy, transplanted late, was harvested on 25 November and the field is now free for wheat. He holds two seed lots: 60 kg of certified PBW 725 bought in October, and about 240 kg of his own PBW 343 seed saved from the same field, where roughly one ear in twenty showed loose smut last March. He intends to sow on 8 December with a zero-till drill at 100 kg/ha (the rate he used last year for a 5 November sowing) and to apply 150 kg urea and 100 kg DAP, all the fertiliser in his store. Canal water reaches his outlet only from 20 December, and his tubewell can irrigate about 0.4 ha per day. Day temperatures in the district are still near 30 °C and the forecast is dry. His neighbour argues that a December sowing cannot pay and advises a late berseem crop instead.
1. Which seed should Harpreet sow, at what rate, and with what treatment? Justify each choice.
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Loose smut is carried inside the grain, so a field where 1 ear in 20 was smutted almost certainly produced heavily infected seed. Seed treatment (carboxin 37.5% + thiram 37.5% at 2 g/kg, or tebuconazole 2% DS at 1.5 g/kg) reduces but does not fully clean a lot with this much infection, and using it untreated would spread smut across the whole field.
Decision:
- Sow the 60 kg certified PBW 725, treated, on the best-drained 0.5 ha.
- For the rest, use the own seed only after brine floatation (discard the floating light grain), washing and drying, then a systemic smut fungicide - never raw.
- Rate: at 8 December he is 2–3 weeks past the normal window; late-sown wheat tillers less, so raise the rate to about 125 kg/ha and sow 4–5 cm deep into moisture.
Arithmetic: 4 ha × 125 kg = 500 kg of seed needed; he has 300 kg. He must buy roughly 200 kg of certified seed rather than stretch the infected lot over 3.5 ha - the cheapest part of the crop to get right.
2. Plan his first irrigation and nitrogen application given the water supply. Give timings and quantities.
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Late-sown wheat has a shallow root system and a very short vegetative phase, so the first irrigation cannot slip.
Irrigation: target the first water at 20–25 days after sowing (about 30 December–2 January). Canal water is available from 20 December, which fits; if the canal is uncertain, the tubewell at 0.4 ha/day means 4 ha needs about 10 days, so start on the lightest, driest field first and finish the whole area inside the window. Do not wait for visible wilting.
Nitrogen: he holds 150 kg urea (69 kg N) and 100 kg DAP (46 kg N + 46 kg P₂O₅) - about 115 kg N, short of the ~150 kg N/ha normally recommended. Buy another 100 kg urea.
Split: one-third of the N with DAP at sowing, one-third at the first irrigation, one-third at the second (booting, about 45–50 days). Apply no nitrogen after the second irrigation: late N on a December-sown crop delays maturity, causes lodging and pushes grain filling into the April heat, which is exactly the risk he is already carrying.
3. Estimate the likely yield penalty and advise whether he should keep the wheat or switch to berseem.
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Each week of delay beyond the last week of November costs roughly 300–400 kg/ha in this district. A 8 December sowing is about two weeks late, so the realistic expectation is around 3.9–4.1 t/ha against a district average near 4.8 t/ha - a loss of about 0.7–0.9 t/ha, with a wide range depending on March–April temperatures.
Berseem is the worse option here. A December-sown berseem gives only one or two light cuts before summer, needs more water than wheat in a canal-limited situation, and surrenders both the wheat straw and the chance of a timely kharif. A late wheat crop still yields more per hectare and per unit of water.
Keep the wheat, but cut the risk:
- use the earliest-maturing, heat-tolerant seed he can buy;
- do not economise on seed rate;
- secure the first irrigation on time and avoid late nitrogen;
- if water becomes critical, shift the berseem to the heavier 1–2 ha as a fodder insurance and keep wheat on the lighter land.