Impact of Leaf Chemical Quality Indices of Different Tree Species on Soil Microbial Biomass and N-Availability in a Wheat Microcosm

Leaves of tropical multipurpose tree species (5 N-fixing, 5 non-N-fixing and combinations of 5 N-fixing species with a non-N-fixing) were incorporated in soil to evaluate effects on soil microbial biomass and N-availability of wheat in a pot experiment under dryland conditions. Soil microbial biomass and N-availability are closely linked to the productivity of an ecosystem. High quality leaves of N-fixing tree species had higher N content, and lower polyphenol (PPL) and lignin (LIG) contents (resulting in lower LIG/N, PPL/N and LIG + PPL/N ratios) than low quality leaves of non-N-fixing species. Combination treatments showed intermediate values of different parameters. Application of high quality leaves caused maximum rise in microbial biomass C and N and available-N in soil; the increase was minimum with low quality leaves and intermediate with combined treatment. Among Nfixing species, Dalbergia sissoo, Cassia fistula and Prosopis cineraria leaf applications showed greater increase in microbial biomass C (128-147% over control) and N (174 - 228%). Strong correlations between LIG + PPL/N ratio of leaves with MBC and MBN of wheat suggests that the ratio can be used to screen multipurpose tree species for use as soil amendment.