Water Budgeting and Enhancing Water Productivity in Lowland Rice-Fish Farming System

Two important problems in lowland rice field include low agricultural productivity and underutilization of excess water. The low productivity is due to excess and deficit water stress in wet and dry season, respectively. Taking advantage of good quality water and heavy textured soil, rice-fish-based farming system is often suggested. Experience with a vertisol in coastal waterlogged area revealed that seepage percolation rate was low (0.47 mm d−1) in November and increased to 1.93 mm d−1 in April. Wet and dry season rice cultivation is feasible with rice-fish system in waterlogged areas by water harvesting and  with irrigation from supplementary farm pond. For this, one-hectare rice-fish system requires supplementary farm pond of 0.18 ha. Similarly, for intermediate lowland in Brahmaputra river valley, supplementary farm pond of 0.18 ha was required for two rice crops in rice-fish system. Six years of study at Brahmaputra river valley revealed that the water productivity of the integrated rice-fish system (1.04 kg rice equivalent yield m−3) was 2.88 times higher as compared to rice fallow system (0.36 kg m−3). For the shallow lowland system, water productivity (0.9 kg rice equivalent yield m−3) with rice-fish system was 2.1 times higher compared to traditional practice of sole rice.