Late-sown wheat after a delayed paddy harvest
Gurpreet Singh has 4 hectares of irrigated land in Ludhiana district. His paddy was harvested on 12 November, but a low patch held standing water for ten days after an unseasonal shower, so the field could be prepared and levelled only by 15 December. He now plans to sow wheat on 18 December. In his store he has 200 kg of PBW 725 seed left from last year, with a laboratory germination of 80 percent. His usual practice for timely sowing is 100 kg seed per hectare on 22.5 cm rows, five irrigations, and 50 kg N, 25 kg P2O5 and 12 kg K2O per acre. A neighbour tells him to sow at the same seed rate and spacing as always, saying wheat is wheat. Gurpreet is reluctant to spend on fresh certified seed and is also considering leaving the field empty until the summer crop.
1. Should Gurpreet use the leftover seed, and at what seed rate should he sow on 18 December? Show your calculation.
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Yes, the seed can be used, but not at 100 kg/ha and not before a quick check.
Why the rate must change: wheat sown on 18 December loses about three weeks of tillering compared with timely sowing, so the crop cannot build yield from tillers. The only compensation left is more main shoots per unit area, which means a higher seed rate. Late-sown wheat is normally sown at about 125 kg/ha instead of 100 kg/ha.
Adjusting for germination: certification assumes roughly 85 percent germination. His lot gives 80 percent, so plant population would fall short. Adjusted rate = 125 x (85/80) = about 133 kg/ha, so sow 130-135 kg/ha.
Quantity: at 133 kg/ha his 200 kg covers only about 1.5 ha, so he must buy certified seed for the remaining 2.5 ha.
Before sowing: run a cloth germination test (100 seeds, moist cloth, 7 days) and treat the stored seed with an approved fungicide, because seed kept over a season carries loose smut and root-rot risk. Narrow the rows to 18-20 cm instead of 22.5 cm so the higher plant population is spread evenly.
2. How should his irrigation and nitrogen schedule change for a crop sown on 18 December, and why?
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The whole schedule moves earlier and tighter.
First irrigation: give crown-root irrigation at about 21-25 days after sowing instead of the usual 30-35 days. Late-sown wheat reaches jointing and flowering in hotter weather, its root system is shallower, and moisture stress at crown-root stage cannot be recovered later.
Later irrigations: keep intervals of 10-12 days rather than the usual two weeks, and expect to need five or six irrigations, not five, because the reproductive phase falls in April-May when evaporation is high. Never skip the flowering and milk stages.
Nitrogen: do not put all the urea at sowing. With 50 kg N per acre, apply the DAP and one-third of the urea at sowing, one-third with the first irrigation and the remaining third with the second irrigation.
Reasoning: a late crop has less time to recover from a setback, so each operation must be on time rather than generous. Extra urea beyond the recommendation only lodges the crop and delays maturity; water timing matters more than water quantity.
3. The field could still be too wet on 18 December. Give Gurpreet a decision rule for sowing wheat versus switching to another crop, with reasons.
Read the worked answer
Fix a cut-off date and decide by it, instead of deciding field by field on the day.
If the field can be worked and sown by about 31 December: sow wheat. Yield will be roughly 15-20 percent below a timely crop, but the extra seed cost is small compared with losing a whole season of land use, and the field still goes into the paddy rotation on time. Wheat also suppresses weeds and adds residues.
If sowing would slip into January: the yield penalty becomes severe (often 25-30 percent or more) and the crop matures late, pushing the next paddy late as well. In that case switch to a shorter-duration alternative such as spring maize, sunflower or a fodder crop, which can still be harvested before paddy transplanting.
Do not leave the field empty: bare land for four months earns nothing, loses organic matter and invites weeds. If nothing can be sown, put in a green-manure crop such as dhaincha or sunhemp and incorporate it before paddy - this is the cheapest way to improve a field that is already being written off for one season.