Shrinking Tank Ayacut and an Unplanned Paddy-to-Cotton Shift
A block-level agricultural officer is reviewing five years of data for a 620 ha village in Sivaganga district. Three interlinked tanks have a registered ayacut of 410 ha, but the area actually irrigated fell from 380 ha to 240 ha. Normal annual rainfall is 900 mm; the last five years averaged 780 mm, with two years below 650 mm. The feeder channel is silted and partly encroached, and the tank bed holds 0.6-0.9 m of silt. Farmers have been replacing paddy with maize and cotton without a block plan. About 60% of holdings are below 1 ha. Paddy nursery raising is becoming difficult because labour is scarce in June, and MGNREGA work competes for the same workers. The officer must advise the panchayat on a realistic cropping plan for the next three seasons and justify it to farmers who believe paddy is the only safe crop.
1. Explain the gap between registered ayacut and actually irrigated area, and assess the agronomic and economic risks of the unplanned paddy-to-cotton shift.
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Registered ayacut is the legal command area recorded for the tank; actually irrigated area is what received adequate water in a season. Here the gap is 410 - 240 = 170 ha, about 41% of the command. The likely causes are reduced tank storage from 0.6-0.9 m of silt, encroachment and silting of the feeder channel, and a rainfall deficit (780 mm against 900 mm normal). A 120 mm deficit is serious because it reduces catchment runoff and tank filling far more than it reduces direct rainfall on the field.
Risks of the unplanned cotton shift:
- Cotton is a 160-180 day crop with a water need of roughly 700-800 mm. If the tank fails at boll formation, yield collapses; maize at 100-110 days has more escape options.
- Cotton is input-intensive and price-volatile. Holdings below 1 ha cannot easily absorb a failed crop plus credit.
- Continuous cotton builds up pink bollworm and other pests and removes the legume break from the rotation.
- The village loses paddy straw for cattle and the lowland paddy ecosystem that suits the tank bed.
- Maize and cotton expansion may also be pushing onto land that is not drained properly, creating waterlogging risk in heavy rains.
The shift is not wrong in itself, but without a water budget and market plan it transfers risk from the tank to the smallest farmers.
2. Prepare a three-season cropping and water-management plan for the village. Show how you allocate land among paddy, maize, pulses and millets, and state the assumptions behind your allocation.
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Start with water, not with crops. Assume the tanks can be desilted and the feeder channel cleared so that reliable supply is restored for about 240-280 ha, not the full 410 ha. Use crop water needs as a first filter: paddy about 1,200-1,500 mm, maize about 500-600 mm, blackgram about 300-400 mm, and finger millet about 400-500 mm. One hectare of paddy therefore uses water that could support roughly two hectares of maize or three of blackgram.
Kharif (June-September): keep paddy on the lowest 100-120 ha of the tank bed, using short-duration ADT 45 or CO 51 and SRI to cut water and seed cost. Put 80-100 ha of upland to maize or finger millet on rainfall plus supplemental irrigation. Avoid cotton on the smallest holdings unless a buyer or gin is contracted.
Rabi (October-January): use residual moisture and canal supply for blackgram or cowpea on 80-100 ha; these fix nitrogen and need little water. Keep a small paddy area only where standing water is unavoidable.
Summer: plan a short pulse or fodder crop only if well water is tested and available; otherwise keep the land fallow or grow green manure.
Assumptions: normal rainfall returns, tank desilting is completed, farmers accept short-duration varieties, and maize/pulse buyers are identified before sowing. If these fail, shift area from paddy to millet and fodder rather than expand cotton.
3. What three field-level checks would you make before recommending this plan, and why could each check change your recommendation?
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Tank storage and feeder-channel condition. Measure the actual silt depth and check whether the channel can be cleared before June. If storage cannot be restored in time, the paddy area must be cut further and the plan should start with a rainfed millet/pulse system.
Soil texture and drainage in the proposed upland blocks. A cotton or maize recommendation on heavy clay with a shallow water table can fail in a wet year. A quick profile check and infiltration test could move those blocks to paddy or to a raised-bed crop instead.
Market and labour check. Confirm whether maize and blackgram have local procurement or a trader willing to buy at a known price, and whether labour is available for cotton picking. If not, the economic case for cotton disappears even if agronomically it can grow.
A fourth check would be well-water quality, because the village may increasingly depend on wells; high salinity would rule out some crops. Each check is a decision gate, not a formality.