Liming One Plot, Not Both
Harjit farms four hectares near Bathinda. A block agriculture office soil test gives his two plots very different readings. Plot A, cropped with wheat for six years and dressed each season with ammonium sulphate, shows pH 5.2 and low available phosphorus. Plot B, irrigated for a decade with slightly brackish tubewell water, shows pH 8.7, with white crusting along the furrows and hard, sticky clods when wet. He has ₹6,000 and can afford any two of: one tonne of slaked lime at ₹2,500, half a tonne of gypsum at ₹2,000, two tonnes of farmyard manure at ₹3,000, or a soil-test-based fertiliser mix at ₹2,800. A neighbour advises him to spread lime on both plots, because lime makes soil sweet and sweet soil grows everything. Harjit also plans to flood Plot A for four months of paddy next kharif, and wants to apply whatever he buys a week before that flooding.
1. Which plot needs lime and which needs gypsum? Evaluate the neighbour's advice using the two pH readings.
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Plot A at pH 5.2 is acidic. Lime (CaCO3, or the faster-acting Ca(OH)2) neutralises the hydrogen ions held on the soil colloids: Ca(OH)2 + 2H⁺ → Ca²⁺ + 2H2O. The pH rises towards 6.5–7.0, and the added Ca²⁺ also helps flocculate the clay. Plot B at pH 8.7 with white crusting is alkaline/sodic: the white deposit is salt left as the brackish water evaporates, and excess Na⁺ on the clay is what makes it sticky when wet and hard when dry. The amendment here is gypsum, CaSO4·2H2O, which supplies Ca²⁺ that displaces Na⁺ from the clay surface; the sodium then leaches away with irrigation and drainage, and structure improves.
Lime on Plot B would push the pH even higher and lock out zinc and iron. So the neighbour's advice is wrong on one of the two plots. It replaces a measurement with a proverb - 'sweet soil' is not a diagnostic category. The judgement is to match the amendment to the measured pH and to the ion causing the problem, not to apply one remedy everywhere.
2. Harjit wants to apply what he buys one week before flooding Plot A for paddy. Give two risks in that plan and state what he should do instead.
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First, paddy is tolerant of acidity - pH 5.2 is close to the range paddy grows well in - so a large lime dose just before paddy spends money on a crop that does not need it, while the crop that is actually losing yield, wheat, gets nothing. Second, lime needs two to three weeks of moist, warm soil to react and be incorporated into the top 10 cm; applied a week before puddling it is unevenly mixed, and the flooding that follows can leave patches of unreacted lime and over-limed spots.
There is also a chemical trap: if lime is spread together with ammonium sulphate, the ammonium is lost as ammonia gas. Keep the two applications weeks apart.
The better sequence is to get a lime requirement figure from the laboratory, apply the calculated dose in the dry field three to four weeks before wheat sowing, incorporate it, and keep paddy as it is. Over-liming above pH 7.5 fixes phosphorus as calcium phosphate and makes zinc and iron unavailable, so the 'low available phosphorus' on his report could actually get worse rather than better.
3. Recommend how to spend the ₹6,000, naming what goes to each plot and one risk in your plan.
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A defensible split is: ₹2,500 for one tonne of lime on Plot A, ₹2,000 for half a tonne of gypsum on Plot B, and the remaining ₹1,500 kept for a repeat soil test after the next harvest. Plot A gets its pH corrected where wheat is limited; Plot B gets a start on sodium displacement without spending money on a treatment that would harm it.
An alternative with better agronomy but a narrower target is ₹2,500 lime plus ₹3,000 farmyard manure, all on Plot A, and to defer Plot B until the brackish water is diluted or blended with canal water - because gypsum without a way to leach the displaced sodium achieves little.
Risk: half a tonne of gypsum over roughly two hectares is well below a full gypsum requirement, so Plot B may show almost no change in one season and Harjit may conclude that gypsum does not work. He should be told to judge Plot B over two or three seasons, with the drain or leaching step in place, and to re-test rather than to trust a single year's appearance.