Water Budget and Crop Choice in a Canal Village
A village in a coastal Andhra district has 120 hectares of irrigated land. The canal, fed by a reservoir, releases water only between June and October and delivers about 0.8 million cubic metres in a good year; in each of the last three years releases were cut by a quarter. Farmers sank 38 borewells after 2018, when farm power became free, and the water table has fallen from 22 m to 31 m. Rainfall averages 640 mm. Paddy, now grown on 95 hectares, needs about 1,200 mm of water; cotton needs 700 mm, red gram 450 mm and millet 350 mm. Salinity in the lower fields has risen and paddy yields have dropped from 5.2 to 4.3 tonnes a hectare. The district administration must advise the village on a cropping plan for the coming year and on whether to stop new borewells. Farmers reply that paddy has an assured procurement price and that any restriction attacks their livelihood.
1. Construct a water budget for the 120 hectares and state the annual deficit in million cubic metres. On that basis, explain why the present cropping pattern cannot be sustained.
Read the worked answer
Convert every crop need to a common unit: 1 mm over 1 hectare is 10 cubic metres.
Demand: paddy 95 ha x 1,200 mm x 10 = 1.14 million m3 (MCM). Cotton on the remaining 25 ha = 25 x 700 x 10 = 0.175 MCM. Total demand is about 1.32 MCM a year.
Supply: canal 0.80 MCM in a good year, but 0.60 MCM at the recent cut of one quarter. Sustainable groundwater recharge is small when rainfall is 640 mm: even at 15 per cent recharge, that is 0.115 MCM, and canal seepage adds a little. Realistic sustainable supply is roughly 0.72-0.95 MCM.
Deficit: about 0.35 MCM in a good year and 0.55 MCM in a cut year. That gap can only be met by drawing down storage, which is exactly what a 9 m fall in the water table shows. A strong answer notes the trap: a wet year does not close the gap, because most of 640 mm of rain evaporates or runs off, and the salinity rise shows that the marginal water being pumped is also the poorer water. Paddy is the problem not because it is a bad crop but because it is the crop with the largest water requirement being grown on the largest area with a supply that is falling.
2. Propose a cropping plan for all 120 hectares that fits within sustainable supply, and justify each crop choice agronomically and economically.
Read the worked answer
A defensible plan keeps household food grain, reduces the thirsty area and puts legumes into the rotation.
Illustrative allocation: paddy 30 ha = 0.36 MCM; cotton 30 ha = 0.21 MCM; red gram 40 ha = 0.18 MCM; millet 20 ha = 0.07 MCM. Crop demand is 0.82 MCM, leaving about 0.10 MCM for leaching salt from the lower fields and for drinking water. Total 0.92 MCM sits inside the 0.95 MCM good-year ceiling and above the 0.72 MCM cut-year ceiling, so the plan needs a rule for deficit years: protect paddy and red gram, defer cotton.
Reasons for each choice: paddy is kept on the best 30 ha because the family needs grain and the procurement price is real, but it is placed on the fields with the least salinity. Red gram fixes nitrogen, breaks the paddy pest cycle and needs only 450 mm, so it earns its place on agronomic grounds as well as water saving. Millet tolerates salinity and can use the lower fields where paddy now fails. Cotton is the cash crop but is water-responsive and pest-heavy, so it is capped rather than expanded.
A weak answer redistributes area without the arithmetic; a strong one shows the plan is feasible in a normal year and says what is cut in a bad year.
3. Compare three instruments - continuing free farm power, banning new borewells, and replacing the power subsidy with a direct benefit transfer plus assured procurement for pulses and millets - and recommend one, giving your reasoning on incentives, monitoring cost and equity.
Read the worked answer
Free power sets the marginal price of irrigation water at zero, so each extra hour of pumping is costless to the farmer and costly to the aquifer. It is popular and easy to run, but it is the direct cause of the 38 wells and the 9 m fall: it rewards exactly the behaviour that must be reduced.
A borewell ban attacks the symptom. It is cheap on paper but expensive to enforce - rigs move at night, 38 wells already exist, and the penalty falls hardest on small farmers who borrowed to drill. Unless the ban is paired with an alternative water source it simply criminalises a coping strategy.
Direct benefit transfer raises the effective price of pumping while keeping income support, so it changes the marginal decision without making farmers poorer. Its costs are metering and political resistance, and it will fail if there is no market for the substitute crops. That is why the procurement guarantee for red gram and millet matters: it lowers the risk of switching, which is the actual barrier.
Recommendation: phase in the transfer and procurement together, keep free power only for wells below a notified depth for three years, and invest the saved subsidy in extension and seed. Equity test: the transfer must be per household, not per unit of power used, or large farmers capture it.