Green Manuring with Sesbania spp. for Maintaining Rice Productivity and Soil Environment

Abstract

A study was conducted at the Bangabandhu Sheikh Mujibur Rahman Agricultural University Experimental Field in July-December 1997 to investigate the effects of green manuring with Sesbania aculeata and Sesbania rostrata on rice productivity and soil environment. Green biomass of Sesbania spp. of 15t ha^-1 was applied to the soil along with inorganic N 0, 20, 40, 60, and 80kg ha^-1, respectively, two weeks before the transplant of a modern rice cultivar of BR11. The highest rice yield of 4.87t ha^-1 was obtained when green biomass was supplemented with inorganic N 80kg ha^-1, which had an increase of 102% and 12% compared to the control plot and the plot where N 80kg ha^-1 alone was supplemented, respectively. No significant yield difference was observed between the plots except the control and where S. aculeata alone was supplemented. However, the highest N-use efficiency was observed in treatments where N 20kg ha^-1 was supplemented with S. rostrata green biomass. Results on soil environmental parameters indicated that green manuring had a beneficial impact on pH, organic-C, NH₄⁺-N, and CO₂-C of soil. Results revealed that CO₂-C were comparatively low in plots where inorganic N was supplemented with or without green biomass at later crop growth stages, which might be due to a probable detrimental effect of inorganic N on the microbial population. From the study, it is concluded that green manuring with S. rostrata of 15t ha^-1 along with inorganic N 20kg ha^-1 might be sufficient for maintaining both satisfactory rice yield and favorable soil environment in acid rice soil under humid sub-tropical conditions.