मृदा स्वास्थ्य कार्ड, आर.एस.सी. वाला पानी और खाद की शिकायत
A farmer in your circle brings a complaint along with a Soil Health Card for his 0.4-hectare plot. The card, sampled 14 months ago, shows pH 8.9, EC 0.62 dS/m, organic carbon 0.31%, nitrogen low, phosphorus medium (18 kg/ha Olsen-P), potassium high (310 kg/ha) and sulphur deficient. His tubewell water has EC 1.9 dS/m and residual sodium carbonate 3.4 meq/L. For the coming wheat season he plans to broadcast 100 kg DAP and 150 kg urea per hectare at sowing, and to flood-irrigate from the tubewell every 8–10 days. He applied gypsum once last June and now believes 'the pH problem is finished'. He also says yields have fallen for three years running and concludes that the dealer's fertiliser is adulterated, 'because nothing else changed'. The district recommendation for wheat is 120 kg N, 60 kg P₂O₅ and 40 kg K₂O per hectare.
1. Compute the nutrients his plan actually supplies, compare with the recommended dose, and state the correction.
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DAP 100 kg supplies 46 kg P₂O₅ (46%) and 18 kg N (18%). Urea 150 kg supplies 69 kg N (46%). Total supplied: N 87 kg, P₂O₅ 46 kg, K₂O nil, sulphur nil.
Against 120-60-40, the gap is 33 kg N and 14 kg P₂O₅. Potassium is the one part he gets right by accident: Olsen-K at 310 kg/ha is high, so skipping K is justified.
A workable correction: about 130 kg DAP per hectare supplies 60 kg P₂O₅ and 23.5 kg N; then urea to cover (120 − 23.5) ÷ 0.46 ≈ 210 kg/ha, split into a basal dose and two top-dressings. Because sulphur is deficient, part of the phosphate should come as SSP, which carries roughly 11–12% S, or 20–25 kg/ha of sulphur should be applied separately. Farmyard manure or a green-manure crop is needed to raise organic carbon from 0.31%. The plan should also be checked against a fresh soil sample, since the card is 14 months old and the irrigation water is changing the soil.
2. Explain, agronomically, why pH 8.9 with RSC 3.4 meq/L water and 0.31% organic carbon explains the yellowing and stunting, and why one gypsum application did not 'finish' the problem.
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pH 8.9 is strongly alkaline. With residual sodium carbonate of 3.4 meq/L, every irrigation adds sodium and bicarbonate faster than leaching removes them, and organic carbon at 0.31% is very low, so there is little organic matter to hold soil structure. The soil is heading towards sodicity: clay disperses, the surface crusts, infiltration falls, and roots meet poor aeration.
At high pH with free calcium carbonate, zinc, iron, manganese and phosphorus are immobilized even when present in the soil. The visible result is exactly what he reports - yellowing of younger leaves, poor tillering, patchy stunting after irrigation.
Gypsum works by supplying calcium that displaces sodium, but the displaced sodium must then be leached out with good-quality water and drained away. Applied gypsum is consumed with each high-RSC irrigation, so a single June dose cannot be a permanent cure. The correct approach is a repeat dose based on soil and water tests, applied and leached before sowing, combined with organic matter and, ideally, blending or changing the water source.
3. Identify the reasoning error in the adulteration claim and state what evidence would actually settle it.
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The inference is post hoc ergo propter hoc, with an added single-cause assumption: yields fell after the fertiliser was used, therefore the fertiliser caused the fall, and 'nothing else changed' is asserted without being tested - while soil pH, irrigation water and organic carbon have visibly changed.
Argument alone cannot settle it; evidence can. First, a fresh soil and water test, because the card is 14 months old. Second, a retained sealed sample of the fertiliser, drawn in duplicate, signed, and sent to the notified laboratory with a forwarding memo; if the analysis is within specification, adulteration is disproved. Third, a comparison strip or plant-tissue/visual diagnosis to test the nutrient explanation.
In the record, note the complaint, the sampling procedure, the seal numbers and the dispatch date, and explain to the farmer in writing why the agronomic cause is the more probable one. That is a defensible conclusion; a bare denial is not.