Conclusion

Based on a series of on site water and salt balance studies, it was suggested that the ordinary eight year rotation system and overirrigation to rice fields have accelerated salt accumulation and concurrently increased abandoned farmlands in the farm. In order to improve the present undesirable situation, it is necessary to lower the ground water table and increase the surface water supply for upland crops.

To reclaim the highly saline soils, leaching experiments were conducted both in the field and laboratory. In both conditions, soluble salts cannot be removed completely from the soil, possibly due to gypsum dissolution. 50% of the initial salinity remained in the soil when Dw/Ds = 1 in the field, whereas in the column experiment with sandy loam soil, only 10% of the initial salinity remained in the soil. Leaching efficiency was similar between intermittent ponding and continuous ponding, and significantly higher than the field result. However, it is expected that higher leaching efficiency will be obtained by ponding water intermittently on the soil surface in the field where the soil texture varies from sandy loam to heavy clay.

The soil saturated hydraulic conductivity was measured using leaching solutions with different concentrations: 0.5, 0.05, 0.01 molc/l (SAR = 10) and distilled water. Similar results in the soil HC were observed when leached with solutions of 0.5 and 0.05 molc/l. However, a decrease of the soil HC occurred with continuing leaching with 0.01 molc/l or distilled water. Clay dispersion possibly caused this decrease. To prevent clay dispersion, the application of flocculant is considered to be promising for keeping the leaching efficiency and irrigation efficiency high.

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