A simple method of producing green manure Sesbania rostrata to achieve N synchrony in lowland rice

Abstract

There is concern, particularly in the tropics, that some high-quality leguminous green manures (LGM) and crop residues may release nitrogen (N) into the soil so rapidly that losses of N may occur through denitrification, ammonia volatilization, and leaching. In Sri Lanka, for example, it is reported that as much as 75% of Sesbania rostrata -N is lost in dry-zone lowland soils (Seneviratne and Kulasooriya 1994). The concept of synchrony of N supply with crop demand has thus resulted. An organic material of the right quality may release N at approximately the same time and rate required by the crop, thereby reducing N losses. This has been tested by mixing lowand high-quality plant materials in different proportions (Myers et al 1994). However, this method adds an additional cost to green manuring because of the labor involved in transporting and applying plant materials with a high C-N ratio. This study investigated a simple cultural method to produce low- and high-quality green manures in situ with S. rostrata .