Late-sown wheat: nitrogen, resistant Phalaris and two canal turns
Harpreet Singh has 5 acres of sandy loam in a canal command area. Paddy was combine-harvested on 20 December and wheat was sown on 28 December, about three weeks after the normal window for his district. At sowing he applied one 50 kg bag of DAP and one 50 kg bag of urea per acre. The first irrigation was given on 18 January. When he walked the field on 5 February (about 39 days after sowing), most plants had only four or five tillers and the older leaves were pale yellow from the tip downwards. A one-acre patch that received clodinafop last winter is still thick with Phalaris minor; he sprayed clodinafop again ten days ago at the recommended dose and sees no effect. He now plans to broadcast two bags of urea per acre in a single application and to repeat clodinafop at double dose. His soil test shows organic carbon 0.31%, low available nitrogen, medium phosphorus and medium potassium. Canal water is assured for only two more irrigations before mid-March; the tube well works but pumping is expensive.
1. Assess his nitrogen programme. What is causing the yellowing, and what would you actually recommend for the rest of the season?
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The uniform pale colour of the older (lower) leaves with thin tillering on a sandy loam is the classic pattern of nitrogen deficiency, but first exclude waterlogging, termite damage to roots, and herbicide injury, since clodinafop can also cause yellowing.
Do the balance sheet: 1 bag urea = 45 kg × 46% ≈ 20.7 kg N, and 50 kg of DAP gives about 9 kg N plus 23 kg P₂O₅. So roughly 30 kg N per acre has been applied. The crop needs about 50 kg N per acre, leaving a shortfall of about 20 kg N – that is one bag of urea per acre, not two. Two extra bags would take the field to roughly 71 kg N, which on a thin, late-sown crop invites lodging, delayed maturity into the heat, late aphid build-up and no extra yield; on sandy loam the surplus also leaches below the root zone.
Apply the single bag with the next irrigation. Because late sowing has already shortened the tillering window, the remaining nitrogen must go early, not after booting. A 2% urea foliar spray (2 kg urea in 100 litres of water per acre) can be used as a quick corrective if the crop still looks pale at booting, but it supplements and does not replace soil-applied nitrogen.
2. How should he deal with the *Phalaris minor* patch where clodinafop has failed, given the crop stage?
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Two consecutive failures of clodinafop at the recommended dose point to herbicide-resistant Phalaris minor in that patch, though application error must be excluded: uncalibrated sprayer, too little water, spraying on a hot afternoon or a missed leaf stage. The weed is already well past the 2–4 leaf stage at which clodinafop works best, so doubling the dose will mostly buy wheat phytotoxicity, not weed control.
The sound choices are: (i) shift to a herbicide with a different mode of action whose label window still covers the current crop stage, and check the current package of practices for the exact product and dose rather than guessing; (ii) for the resistant patch, hand-pull or hoe the escapes and clip the remaining weeds before they set seed, so the seed bank is not topped up for next year; (iii) plan the next season around rotation, not repetition – a pre-emergence herbicide at sowing, a post-emergence product from a different group, clean seed, and a non-cereal break crop wherever possible. Applying 2,4-D now, close to jointing, risks spike malformation and should be avoided.
3. He has only two canal turns left before mid-March. Which irrigations should get them, and why?
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With only two assured turns plus costly tube-well water, allocation has to follow the stages where moisture stress hits yield hardest. Use the first turn at tillering, because the top-dressed urea only works after it dissolves into moist soil and because tiller survival is still being decided. Reserve the second turn for booting, when the ear is forming and flowering is imminent; this is the most stress-sensitive stage in wheat, and missing it damages grain number more than missing any other single irrigation.
If tube-well water is affordable, add a light irrigation at milk for test weight, but never irrigate near maturity or on a windy afternoon. Practical support measures matter as much as timing: laser-levelled field so each turn spreads evenly, irrigating at night to cut evaporation, and checking that the low corner is not waterlogged. For a late-sown crop that will mature into rising temperatures, the priority is to keep the crop growing now, not to save water for a fourth irrigation that may not be needed.