Wheat at jointing with a 9-day warabandi: spend the water now or save it for flowering?
Sunita has 2.4 ha of wheat (HD 3086) in Hisar, sown on 24 November after paddy. Her canal outlet runs a 9-day warabandi and her turn gives six hours of water for her 0.5 ha share; a 5 HP submersible fills the gap but power arrives for only about four hours on most nights. Pan evaporation at the block station is 3.5 mm per day. She gave the first irrigation at 28 days, after the crown-root stage had passed, and the crop is now at 45 days and jointing, with cracks beginning to open in the sandy loam. Her neighbour advises her to skip this irrigation and "save the water for flowering". Last year she irrigated heavily and applied an extra 60 kg N; the crop lodged and yielded 4.2 t/ha. She wants the most grain from the water she can actually command, not the largest number of irrigations.
1. Rank the irrigation stages of wheat by criticality and state how many irrigations Sunita can realistically plan with her water.
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Criticality order for wheat:
- Crown-root irrigation (CRI), 20–25 days after sowing - the single most important irrigation; ear initiation and tiller survival are decided here.
- Flowering (around 65–70 days) - the most sensitive stage for grain set; stress here cuts grains per spike.
- Milk stage - needed for grain filling and test weight.
- Jointing/booting - important but not as decisive as flowering.
- Dough stage - the first one to drop when water is short.
Her position. She has already lost the CRI timing; that loss cannot be recovered by irrigating heavily later - it simply adds lodging risk. With a canal turn every nine days plus about four hours of night power, she can realistically deliver four to five irrigations of about 6 cm each. A sensible plan is: light irrigation now at jointing, then flowering, milk and, if water allows, dough. If only three remain, she should protect flowering and milk and drop dough.
Timing aid: with 6 cm irrigation water, wheat is normally irrigated when cumulative pan evaporation since the last irrigation reaches about 65–75 mm (IW/CPE ratio 0.8–0.9). At 3.5 mm/day that is roughly three weeks - she should not simply copy the neighbour's calendar.
2. Evaluate the neighbour's advice. What is the likely cost of skipping the irrigation at jointing?
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The advice is only half right. Saving water for flowering is sound if the water saved is genuinely available then and the crop can survive the gap. On a sandy loam with pan evaporation of 3.5 mm/day, the profile holds limited moisture, and a crop at jointing is expanding leaf area fast; a long dry spell now reduces spikelet number and tiller survival, and yield can drop by roughly 10–15% even if flowering is later watered well.
The better judgement is a moderate irrigation now, not a heavy flooding: about 5–6 cm using the night power, which keeps the crop growing and still leaves the canal turn for flowering. The previous season's lodging is a warning about depth and nitrogen, not about irrigating at jointing - heavy ponding plus 60 kg of extra N on a tall crop is what pushed it over.
Decision rule for her: never risk flowering, always secure CRI in future years, and use jointing and dough as the adjustable stages. If the tube well fails and she must choose one stage only after jointing, choose flowering.
3. What practical measures would get her more grain per unit of water, and how do you explain last year's lodging at 4.2 t/ha?
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More crop per drop:
- Laser-levelling the field, so water does not run to the low corner and leave high spots dry.
- Irrigating to a measured 6 cm rather than flooding until the water stands; use the full warabandi turn efficiently by irrigating in strips.
- Irrigating at night where power allows, cutting evaporation losses.
- Retaining or mulching with paddy straw (2–3 t/ha) to slow surface evaporation and reduce crusting.
- Applying nitrogen in three splits and stopping nitrogen after flowering; extra N late in the season softens straw and invites lodging.
- Recording dates of sowing, irrigation and nitrogen, so next season's plan rests on data, not memory.
The lodging: the combination of a heavy irrigation, an extra 60 kg N and a well-fed canopy produced tall, soft stems that could not carry the ear; once lodged, grain filling and test weight fall. The fix is not less water everywhere but balanced nitrogen and controlled depth - a lodged crop also wastes every irrigation it received, which is why the water accounting and the fertiliser decision belong together.