Use of green manuring crops in rice fields for sustainable production in Bangladesh agriculture

Abstract

About 2.4 million hectares of modern rice varieties are grown over the high and medium-high lands of Bangladesh, mostly under rainfed lowland culture. The efficiency of inorganic N fertilizer under such a rainfed ecosystem is low where soils undergo alternate wet-dry cycles. Legume green manuring crops have the ability to fix a considerable amount of atmospheric N and can add both N and organic matter to soil if rightly incorporated. Because of the high price and low efficiency of inorganic N fertilizer and also the low organic matter content of Bangladesh soil, the inclusion of green manuring crops in a rice-based cropping system, particularly rainfed lowland rice ecosystems, has received priority consideration during the recent past. A number of studies on different aspects of green manuring crops were made at Bangladesh Rice Research Institute (BRRI) to evaluate their effectiveness as supplemental sources of N for rainfed lowland rice. Results showed that the potential of cowpea (Vigna unguileata) was much higher than that of dhaincha (Sesbania aculeata), as a green manuring crop, with respect to mineral composition and its influence on rice yield. However, incorporation of the dhaincha green manuring crop in a Boro-T. Aman cropping system can save about 70 kg N ha⁻¹ yr⁻¹ in the long term. Results further showed that Sesbania rostrata was superior to other species with respect to biomass production and accumulation. In a light textured soil in a low-rainfall area, Sesbania green manuring was found to be more effective and even 45-day-old Sesbania had the ability to completely substitute 90 kg/ha urea-N in the next crop of rainfed lowland rice. In a heavy textured soil in a high-rainfall area, stem cutting of Sesbania rostrata was found to be superior to other planting practices and had the ability to supplement almost the entire amount of N in the next crop of rainfed lowland rice. Dhaincha green manuring as intercropping with T. Aus in a T. Aus-T. Aman cropping pattern also showed some promise. Sesbania N was more efficient when the time gap between incorporation of Sesbania and transplanting of rice seedling was the smallest.