Acceso usuarios
Man Singh, Sunil Pabbi, A.K. Bhattacharya, Anil Kumar Singh
India has a total coastline of about 7000 km. The major vocation in the densely populated coastal region is agriculture. The majority of the coastal soils are waterlogged, saline to saline�sodic, low in carbon content and poor in productivity. The nitrogen dynamics of the coastal rice wetlands reclaimed by subsurface drainage was studied. Four areas with various drain spacings and two distinct stages of reclamation were considered. The land reclamation process through subsurface drainage of the areas with drain spacings of 15 and 25 m was started in 1986 and 1987, respectively. For the areas with 35 and 55 m drain spacings, the reclamation process was started in 1999. The data collection was carried out during 1999, 2000 and 2001. During the period of study, irrigated rice was cultivated in the areas with 15, 35 and 55 m drain spacings where the subsurface drainage system was operational. Drainage operation for the area with 25 m drain spacing was discontinued and the land left fallow. The study revealed that subsurface drainage improved the fertility status of the soil by promoting ammonium storage on the clay complex. Sustained operation of subsurface drainage system could maintain a favourable salt balance in the topsoil layer (0�30 cm) enhancing microbial activity and consequently nitrification. As a result, the nitrite concentration in soil water at field capacity was within the permissible limit of 0.9 mg/L in the rhizosphere. There was, however, a higher amount of nitrite accumulation in the area with impeded drainage. The three years� data also established a gradual increase of nitrite accumulation in the 0�15 and 15�30 cm soil layers respectively. The nitrite concentration in these layers exceeded the permissible limit one year after discontinuation of the operation of the subsurface drainage system. Such a nitrite accumulation in the topsoil layer may give rise to nitrite toxicity to plants and become a threat to the sustainability of the coastal agro-ecosystem
