Influence of subsurface drainage on crop production and soil quality in a low-lying acid sulphate soil

Kuttanad, the low-lying tract in Kerala State of south-west India, is a place where drainage problems have caused the agricultural production to remain low. The problem is more severe in the acid sulphate soils of Kuttanad. Besides the problems inherent to acid sulphate soils, the area also experiences problems of flooding, lack of fresh water and intrusion of saline water from the Arabian Sea. A subsurface drainage system consisting of 10 cm diameter clay tiles, each of 60 cm length, was installed at a depth of 1 m with two different spacings of 15 and 30 m for evaluating its influence in improving soil quality and crop production. Many of the critical crop growth parameters in the subsurface drained area, particularly the grain yield and 100 grain weight, were significantly superior to that of the ill-drained areas. Drain spacings up to 30 m was found to significantly improve the productivity of the area. The overall increase in rice yield due to subsurface drainage was 1.36 t/ha. It was also found that subsurface drainage could remove the chemical heterogeneity of soil which is the root cause for patchy crop growth and uneven ripening of rice crop in the area. Acidity in the subsurface drained area was always lower throughout the cropping season. The salinity in the soil could be controlled considerably by subsurface drainage. The iron transformations were not serious enough to cause concern for rice cultivation when subsurface drainage was adopted. Accumulation of sulphates in insoluble form occurred during drainage due to the oxidation of pyrite. Subsurface drainage was also very efficient in leaching sodium, calcium and magnesium. Chloride content in soil decreased drastically during drainage.