Difference in phosphorus response among tropical green manure legumes grown under limed and unlimed soil conditions

Two pot experiments were conducted to investigate the effect of phosphorus fertilization on the growth of some tropical green manure legumes cultivated under limed and unlimed soil conditions. The species used were Cassia occidentalis, Cassia tora, Crotalaria juncea, Glycine max, Sesbania cannabina, and Sesbania rostrata. The species differed in their response to lime application. Liming increased the dry matter yield of Cro. juncea, G. max, S. cannabina, and S. rostrata while it decreased the dry matter yield of Gas. occidentalis and Cas. tora. Liming decreased the concentrations of P, Fe, Mn, and Zn while it increased the concentration of Ca in all species. The Mg concentration decreased in Cas. occidentalis and Cas. tora by liming while it increased in other species. The cause of the growth depression resulting from liming depended on the species. The growth reduction in Cas. occidentalis, Cas. tora, and Cro. juncea was due to the low concentration of P in the plant tissues. The deficiency in Zn was also a factor in the growth depression of Cas. tora. Cro. Juncea was found to be the most sensitive species to soil acidity. The application of P fertilizer resulted in the improvement of the dry matter yield, nodulation, nitrogen fixing activities, and nitrogen uptake. S. cannabina and S. rostrata were noted to be more efficient species in utilizing phosphorus in soil, and less responsive species to the application of higher level of phosphorus fertilizer. On the other hand, Cro. juncea was found to be the least efficient species in the utilization of P, and the most responsive species to phosphorus application. It was confirmed from this experiment that sesbania sp. were useful manure legumes due to their ability to improve P availability in soils with low available P content through their decomposition, and that G. max and Cro. juncea were effective legumes showing a high biomass production under moderate soil P fertilization