Salinity, Silt and the Choice of a Crop in a Sundarban Mouza

Chain of cause and effect:

1. Breach allows tidal ingress. Sea water has an electrical conductivity in the tens of dS/m, far above the 2.1 dS/m the field once held.
2. Salt is left behind, not washed away. Tidal water stands on the field; when it evaporates in the dry season the dissolved salts stay in the topsoil. Repeated cycles concentrate them, taking EC from 2.1 to 6.8 dS/m - a threefold rise.
3. The plant feels it physiologically. Above roughly 4 dS/m, paddy struggles to draw water osmotically even from wet soil, and sodium toxicity damages roots and blocks uptake of nutrients. Growth and grain filling both fall.
4. Result: 3.9 to 1.6 t/ha, a 59% loss. That is consistent with a soil now well above the tolerance threshold, not with a one-off bad season.

Two supporting links that candidates often miss:

• The 1,750 mm of rain is enough to leach salt, but only if the field drains and there is fresh water to replace it. Where the repaired embankment holds water in and the canal network is silted, the rain cannot flush the profile.
• The deep tube well adds a second problem. Heavy pumping since 2015 lowers the fresh-water head, letting saline water move in laterally. Salty drinking water and saline soil are the same story, not two separate ones.

Where the claim is right: per hectare, bagda earns several times what a 1.6 t/ha paddy crop does. On a purely private, per-hectare calculus, the 40 households with the capital to raise plots to 1.2 m and lease tidal water have found the higher-return use. That is a real signal and should not be dismissed.

Where the claim fails: it measures one hectare and one household, not the village.

• It is a zero-sum water decision. Bagda needs brackish water held on the land, so salinity is now a condition of production. Every hectare converted makes it harder to bring neighbouring plots back to paddy; the externality is pushed onto the other 220 households.
• Employment collapses. Paddy employs many hands at transplanting and harvest; a shrimp pond employs very few. Forty households gain, but the landless lose their main source of wage work, grazing and fuel.
• Risk concentrates. One export market, one disease outbreak, one cyclone. The 2020 cyclone destroyed 60 houses; a breached pond would also dump saline water on a neighbour.
• Paddy income is not the same as paddy revenue. It includes subsistence grain and fodder that never appear in a market price.

Conclusion: 'profitable' is true per hectare, false per household and per village. A defensible policy allows some ponds but zones them away from paddy and drinking-water sources.

Priority: desilt and re-excavate the canal network, paired with the rainwater tanks as a low-cost add-on. Fund the embankment last, and only as a set-back earth embankment with mangrove planting.

Reasoning:

• EC is 6.8 dS/m and the rain is 1,750 mm. The limiting factor is not rainfall but drainage and a supply of fresh water to push salt down the profile. A silted canal gives both: it carries surplus monsoon water off the field and brings fresh water in. That attacks the measured cause; a taller wall does not.
• The canal also recharges groundwater, which eases the falling static level and reduces the saline intrusion into the aquifer that made the tube well salty.
• Rainwater harvesting in every homestead is cheap, decentralised, and directly addresses the salinised drinking-water pond. It is the one measure that works immediately after the next cyclone.

The other two are still needed because: the tanks cannot flush 190 ha of soil; and the embankment is not useless, it is simply mistimed. A taller concrete wall on a subsiding, breached alignment has already failed once. A set-back embankment with a mangrove belt absorbs surge energy instead of resisting it, and leaves a drainage outlet.