White Crusts in a Canal Command: Salinity, Sodicity and the Paddy Proposal

Diagnosis - three signals, one process

1. Waterlogging. A water table of 0.9 m in July and 1.4 m in October sits inside the capillary fringe for these soils (roughly 1–1.5 m). Evaporation therefore pulls water to the surface and leaves salts behind - which is why the crust appears after the Rabi harvest, when the soil dries.
2. Salinity. ECe 5.6 dS/m is above the ~4 dS/m threshold at which wheat yield begins to fall steeply. The observed drop of about 38% (4.2 to 2.6 t/ha) is consistent with salinity plus waterlogging acting together; the two usually reinforce each other because waterlogged roots have less oxygen to cope with salt.
3. Sodicity. pH 8.4 with SAR 14 means sodium, not just chloride and sulphate, is the problem. Sodium disperses clay, seals the surface, cuts infiltration and keeps the water table high - a feedback loop.

Standing water for 20–25 days shows there is no effective drainage outlet; canal seepage plus over-irrigation recharge more than the crops transpire.

Verdict on paddy: not defensible. Paddy has a far higher water duty than wheat or mustard. It would raise the water table, enlarge the waterlogged area, and paddy itself is sensitive to salinity at establishment and to sodicity. An extra outlet increases supply, not drainage - it treats the symptom in the wrong direction.

Order of operations that follows from the diagnosis

• Cut recharge: laser levelling, rotational (warabandi) supply, no flood pre-irrigation, lining or sealing the distributary.
• Provide surface/subsurface drainage with a safe disposal route - without this, any leaching just moves salts around.
• Apply gypsum at a rate set by soil SAR and cation exchange capacity, then leach with good-quality water.
• Shift to low-duty, salt-tolerant crops (barley, mustard, cotton, ber, fodder) rather than paddy.
• Treat tubewell subsidy cautiously: pumping can lower the water table, but only if the groundwater EC is tested and used conjunctively.

This answer would change if a functioning drainage outlet existed and ECe were below about 2 dS/m; then higher-value crops become arguable.

Purpose first. Monitoring must distinguish three questions: is the water table falling, is the salt store in the root zone shrinking, and is the sodium hazard being reduced? A single indicator cannot separate these.

Design

• Water table: a nested piezometer network - at least one per 10 ha, stratified by distance from the distributary and by elevation, with continuous recorders on two fields. Read fortnightly during canal runs and monthly otherwise; include a pre-monsoon (June) and post-monsoon (October) census, since those two dates define the annual range.
• Soil: sample 0–30, 30–60 and 60–90 cm in the same permanent plots each season. Measure ECe (saturation extract), pH, SAR and infiltration rate. Permanent plots stop the classic error of comparing different fields each year.
• Water balance: record canal supply (discharge × days), rainfall, pumping hours and crop evapotranspiration. Without the balance you cannot say whether a falling water table is due to drainage or simply to a dry year.
• Drainage outflow: volume and EC of water leaving the drains; this is also the environmental compliance point, because saline outflow has to go somewhere.
• Crop and social data: yield per plot, area sown by crop, and cost per hectare, so that adoption can be judged, not just hydrology.
• Remote sensing: one post-monsoon satellite index of surface salinity/crusting per year as a cheap spatial check.

Thresholds that should force a re-think

1. Water table shallower than 1.5 m at pre-monsoon after year 2 - drainage capacity is inadequate.
2. ECe in the 0–30 cm layer not falling by at least 30% after two leaching seasons - gypsum rate or leaching efficiency is wrong.
3. SAR rising despite gypsum - the amendment dose is being calculated on the wrong basis, or sodium-rich water is being used.
4. Drain outflow EC above the agreed limit - the system is exporting the problem downstream, and the disposal route needs redesign.

Report against a fixed baseline plot set, and publish the data to the panchayat; a monitoring plan that only the department sees cannot correct farmer behaviour.

Why the current subsidy is mis-targeted

• Tubewells address the water table but not the salt. Pumping can make things worse if the groundwater itself is saline (common in canal commands), because the farmer then irrigates with the very salt that needs removing. It also rewards capital, so larger holdings capture most of it, and unregulated well density simply moves the problem.
• Gypsum is chemically the right response to SAR 14, but gypsum without drainage and leaching water leaves the sodium in the profile. Applied to a sealed, low-infiltration surface it may not even enter the soil. A subsidy for a material, with no test and no water plan, buys bags, not reclamation.

A better design

1. Pay for practices, not assets: per-hectare payments for laser levelling, for adopting low-duty crops (barley, mustard, fodder), and for maintaining the warabandi schedule. These are reversible and can be withdrawn.
2. Make gypsum payment conditional on a soil test and a leaching plan, with the dose written on the voucher and verification after one season. This converts a material subsidy into a service.
3. For tubewells: subsidise only after an EC test, require registration of the well, and cap well density per unit area. Conjunctive use - canal water blended with groundwater - should be the stated purpose, not groundwater substitution.

Who pays for drainage

Drainage is a public good with off-site beneficiaries: the distributary system, downstream farmers and the village itself all gain when the water table falls. No individual farmer will invest, because the benefit leaks away - this is exactly the collective-action case for public funding. A defensible split is: the command-area development programme funds the main drains and outlet; the panchayat maintains the field drains through a labour component; beneficiaries contribute land for the drain alignment and a small share of maintenance. Disposal of saline outflow must be designed and permitted before construction, not after, or the scheme simply relocates the damage.