Effect of combined nitrogen on nodule function of leguminous crops with special reference to tropical soils

Abstract

The effect of combined nitrogen on nitrogen fixation has been discussed by several investigators and from their findings it could be concluded that inorganic nitrogen may have either stimulatory, neutral of negative effect on nitrogen fixation depending on the type of legome and soil condition. It was reported in some instances that low levels of combined nitrogen especially when applied as a "Starter" fertilizer at germination, stimulates plant growth and enhances nodule mass and nitrogen fixation. On the other hand when most of the legumes are grown in soil high in available nitrogen, the nitrogen fixation rate is severely affected. This phenomenon may become more critical when legumes are grown as cover crops where non legume counterpart is fertilized with nitrogenous fertilizer. The degree of inhibition appears to vary with sevaral factors vis, concentration of combined nitrogen, host species, cultivar, strain of root nodule bacteria, rate of inculation, light intensity and temperature. However, the most critical factor is the concentration of combined nitrogen and it has been shown that very low concentrations such as 240 ppm N reduced