Soil Test, Saline Water and a Paddy Relapse
A newly appointed AFO visits Rampur village in a canal command area to advise a farmer holding 6 ha of sandy loam soil. The soil test report shows pH 8.6, EC 0.9 dS/m, organic carbon 0.31%, available nitrogen low, phosphorus medium and potassium high. The canal supplies water only once every 12 days, and the farmer's borewell water has EC 3.2 dS/m. In the last kharif season he grew paddy and lost about 40% of the crop to false smut and lodging after applying 140 kg N/ha in three splits. He now plans paddy again in kharif and wheat in rabi, and asks whether he should increase urea to compensate for the low nitrogen. The farm has no soil-test-based fertilizer plan, and the farmer has not maintained records of input costs or yields.
1. Identify the two most important constraints in this field and explain why increasing urea would not solve them.
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The two binding constraints are (i) soil alkalinity/salinity risk - pH 8.6 with EC 0.9 dS/m and borewell water at EC 3.2 dS/m - and (ii) a 12-day canal interval that cannot support continuous standing water for paddy. Low organic carbon (0.31%) and low available N are secondary because they can be corrected, but adding more urea would worsen the problem: 140 kg N/ha already produced lodging and false smut, both favoured by excessive nitrogen and a dense canopy. More urea would increase lodging risk, raise input cost, and add salt load without improving water availability or reducing pH. The first interventions should be organic matter (FYM/green manure), gypsum or another amendment if exchangeable sodium is high, and a crop that fits the irrigation interval; fertilizer should be split and guided by the soil test, not increased blindly.
2. Recommend a kharif and rabi crop/irrigation plan that fits the 12-day canal interval and the saline borewell.
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Do not repeat paddy with the same plan. For kharif, choose a shorter-duration, salt-tolerant crop such as maize, sorghum, pearl millet or cotton, sown on ridges; if paddy is unavoidable, use a salt-tolerant, short-duration variety and direct seeding rather than continuous flooding. Use canal water at critical stages and blend borewell water with canal water; avoid irrigating with EC 3.2 water at germination. For rabi, wheat can be grown with 4–5 limited irrigations if canal water is stored in a farm pond; otherwise choose barley, mustard or chickpea, which need fewer irrigations. Apply 5–10 t FYM/ha before kharif, and keep a leaching dose once a year only if drainage is adequate.
3. Draft a soil-test-based fertilizer adjustment: what should the farmer do with N, P, K and organic carbon?
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N: do not exceed 100–120 kg N/ha; apply one-third basal, one-third at tillering and one-third at panicle/ear initiation; use neem-coated urea. P: soil P is medium, so apply 40–50 kg P2O5/ha at sowing/transplanting. K: soil K is high, so skip potassium fertilizer this season and re-test after harvest. Organic carbon: apply 5–10 t FYM/ha or a green-manure crop; this also improves water-holding capacity. At pH 8.6, apply zinc sulphate 25 kg/ha and monitor EC; do not add more salt-based fertilizers. Keep a simple record of inputs and yields so the next recommendation is based on crop response, not only on the soil test.