Late Boro after Potato: Seed Rate, Method and Fertiliser Stock
Ashok Halder of Dhaniakhali, Hooghly, has 0.40 ha of medium land under potato until the third week of January. He wants to take boro paddy immediately after the potato harvest and has a shallow tube well that can irrigate 0.40 ha. He has budgeted ₹9,000 for seed and has four family workers plus hired labour at ₹350 per day. The block Krishi Sahayak advises transplanting a 145-day variety on 22 January, which would push harvest into mid-June. Ashok is weighing two options: (a) raise a nursery and transplant, or (b) direct-seed pre-germinated seed on 25 January. In his store he has 20 kg urea, 30 kg DAP and 10 kg muriate of potash, and his last soil test showed zinc at 0.42 ppm. Boro paddy sells locally at about ₹2,200 per quintal at harvest, and last year his neighbour lost about 20% of grain to sterility after a hot April.
1. Work out the seed requirement for transplanting and for direct seeding on his 0.40 ha, and recommend which method fits his situation.
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Transplanted boro with a conventional variety takes 40–50 kg seed/ha, so 0.40 ha needs 16–20 kg; the nursery bed would be roughly 1/20 of the main field, about 200 m². Direct seeding of pre-germinated seed needs 60–80 kg/ha, i.e. 24–32 kg. At ₹40–50/kg the whole seed bill is under ₹1,600 against a budget of ₹9,000, so seed cost does not decide the matter - time and labour do.
Because his land is free only in the third week of January, transplanting a 145-day variety would push flowering into late April–May. Every day saved matters, so direct seeding on 25 January with a short-duration (about 120–125 day) variety is the better fit: it saves 20–25 days of nursery plus 8–10 labour-days of uprooting and transplanting (roughly ₹3,000–3,500). The price is that the field must be well levelled, drained and weed-free; he must use a pre-emergence herbicide (butachlor or pendimethalin) plus one hand weeding, and sow slightly thicker to cover gaps.
2. Which agronomic risks does a 22 January transplanting of a 145-day variety create, and how would you reduce them?
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The binding risk is high-temperature damage at flowering. Transplanted on 22 January, a 145-day variety flowers in the third week of April and fills grain in May, when shade temperature often crosses 35 °C and nights stay above 25 °C. At anthesis, even 1–2 hours above about 35 °C sterilises spikelets; the neighbour's 20% sterility loss is exactly this. Warm nights also raise respiration, reduce grain filling and give chaffy grain of low test weight.
How to reduce it:
- choose an early, short-duration variety and start as soon as the potato harvest allows;
- keep 5 cm of standing water at booting and flowering, since water moderates canopy temperature;
- avoid late top-dressing of nitrogen, which delays maturity and invites brown planthopper;
- split the potash dose for stem strength;
- harvest promptly at maturity so grain does not shatter in the norwester.
A late crop can still be saved, but the correct judgement is to advance the harvest rather than chase yield with extra fertilizer.
3. Using the fertilizer stock he already holds, work out what is still short for 0.40 ha and what he should buy, keeping the low zinc in view.
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The recommended boro dose is about 100:60:40 kg N:P2O5:K2O per ha, so for 0.40 ha he needs roughly 40 kg N, 24 kg P2O5 and 16 kg K2O.
What he holds:
- 20 kg urea = 9.2 kg N
- 30 kg DAP = 5.4 kg N + 13.8 kg P2O5
- 10 kg MOP = 6.0 kg K2O
Total in hand: 14.6 kg N, 13.8 kg P2O5, 6 kg K2O.
Gaps: about 25 kg N (≈55 kg urea), 10 kg P2O5 (≈22 kg DAP) and 10 kg K2O (≈17 kg MOP). He should buy about 55 kg urea, 22 kg DAP and 17 kg MOP, splitting the urea into basal, tillering and panicle-initiation doses.
Zinc at 0.42 ppm is below the 0.6 ppm critical level, and boro after potato often shows khaira. He should add 10 kg zinc sulphate for 0.40 ha (25 kg/ha) at the last ploughing, or give two 0.5% foliar sprays at tillering and panicle initiation. Zinc must not be banded together with phosphatic fertilizer.