Effects of soil fertility and fertilizer application on biomass and chemical compositions of leguminous cover crops

The biomass and chemical compositions of selected leguminous cover crops Aeschynomene histrix, Cajanus cajan, Centrosema brasilianum, Centrosema pascuorum, Chamaercrista rotundifolia, Crotalaria verrucosa, Lablab purpureus, Psophocarpus palustris, Pseudovigna argentea, Mucuna pruriens, Pueraria phaseoloides, and Stylosanthes hamata were studied in a pot experiment, using soil with two fertility levels. Biomass yield responded to soil fertility levels and fertilizer application. The highest response to soil fertility was observed with C. brasilianum (340%, 200% and 310% more shoots, roots and nodules in high fertility soil than low fertility soil without fertilizer application). The highest response to fertilizer application was with P. palustris (500% more shoots with fertilizer than without in high fertility soil), with C. rotundifolia (410% more roots with fertilizer than without in low fertility soil), and with L. purpureus (1330% more nodules with fertilizer than without on high fertility soil). Legumes grown without fertilizer application allocated more biomass to roots than those with fertilizer application. Chamaercrista rotundifolia, L. purpureus, P. argentea, M. pruriens and C. cajan showed higher N content in roots than in shoots. Soil fertility levels did not affect N content of shoot, while fertilizer application increased it by 30%. Except for C. cajan (only shrub species), all the herbaceous legumes had lower lignin content (6–10%) in the shoots. The mean lignin content in roots was above 20% with no fertilizer, and decreased with fertilizer application compared to the no fertilizer treatment. The polyphenol concentration in shoots was higher than in roots.