Reclaiming a Saline-Sodic Paddy Field in Coastal Odisha
Ramesh farms 0.6 ha of lowland paddy in Mahakalapada block, Kendrapara, Odisha. The field is irrigated by a canal whose water has an electrical conductivity (EC) of 1.1 dS/m. A soil test taken before kharif reports pH 8.4, ECe 7.2 dS/m, ESP 28%, CEC 18 cmol(p+)/kg, organic carbon 0.42%, and infiltration 2 mm/h. The 25-day-old transplanted rice is patchy: stunted plants with whitish leaf tips and poor tillering, especially in the lower corner where water stands 5 cm deep. The field has no subsurface drainage. The farmer has 2 t of gypsum, 15 t of FYM, and access to a shallow tube well, but the canal is the only source of good-quality water. He plans to broadcast all the gypsum in the standing water and continue with the same crop. Rainfall is about 1,200 mm, mostly June to September. The lower corner has a monsoon water table at 40 cm, and the field slopes gently toward the canal. Ramesh also wants to grow a rabi crop if the land can be reclaimed.
1. Interpret the pH, ECe, ESP and infiltration values. Is the immediate problem salinity, sodicity, or both? Explain why the farmer's plan of applying all gypsum in standing water is unlikely to solve the problem.
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Diagnosis. ECe 7.2 dS/m is above the 4 dS/m salinity threshold, and ESP 28% is above the 15% sodicity threshold; pH 8.4 and infiltration 2 mm/h fit a saline-sodic soil. The patchy whitish tips and poor tillering are consistent with salt injury and poor root growth, worsened where water stagnates. Both salinity and sodicity matter, but the immediate limitation is that salts cannot be leached because there is no subsurface drainage.
Why the plan fails. Gypsum supplies Ca2+ to displace Na+ from the exchange complex, but the displaced Na+ must be leached below the root zone. Broadcasting all 2 t into standing water without drainage leaves the salts in the field and may not mix the gypsum into the soil. A rough check: with CEC 18 cmol/kg and ESP 28%, reducing ESP to 10% means removing about 3.24 cmol Na/kg. For 0-15 cm soil (about 2.1 million kg/ha), that is about 1.56 t Na/ha, requiring about 5.8 t gypsum/ha theoretically. On 0.6 ha that is about 3.5 t, so her 2 t is short even before field efficiency is considered. Confirm with the laboratory gypsum requirement.
2. Prepare a practical reclamation and crop plan for the next two seasons, including gypsum dose, FYM, drainage, water source, and crop choice. State what you would do for the current rice crop.
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Current crop. Do not expect a rescue with a heavy gypsum dose. Open shallow drains if possible, maintain only a thin water layer, avoid letting canal water evaporate to concentrate salts, and harvest the crop for what it is. Do not apply urea to 'push' growth; the problem is not simply N.
After harvest. 1) Sample 0-15 and 15-30 cm and get gypsum requirement, ECe, ESP and pH. 2) Install temporary shallow drains (30-40 cm deep, 5-10 m apart) or broad beds so leached salts have an outlet. 3) Apply the full gypsum requirement in two splits, incorporated into the top 10-15 cm, not into standing water. 4) Add 10-15 t FYM/ha and a green-manure crop such as dhaincha. 5) Leach with canal water when drainage works; aim for ECe below 4 dS/m before the next rice crop. 6) Grow a salt-tolerant rice variety in kharif; in rabi, grow only if good water and drainage are available, otherwise keep the land under a tolerant cover crop. Do not puddle immediately after gypsum; allow calcium to react and salts to move.
3. What indicators would you monitor to decide whether reclamation is working, and what would make you change the crop or the water source?
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Monitor ECe, ESP, pH, infiltration and water-table depth at 0-15 and 15-30 cm before each season; record crop survival, tillering and yield. Reclamation is working when ECe falls below 4 dS/m, ESP below 15%, pH trends toward 8.0 or lower, infiltration exceeds about 5 mm/h, and the lower corner no longer stays waterlogged. If ECe stays above 4 dS/m after two leaching seasons, or if drainage cannot be installed, shift to a more salt-tolerant crop and stop pumping brackish water. If canal water becomes scarce, reduce the area rather than spreading the same water thinly.