Implications of multipurpose tree leaf application on wheat productivity in dry tropics

Abstract

Leaves of multipurpose tree species (those providing more than one function or product of human use) can serve as sources of fertilizer for nutrient supply, especially nitrogen (N). In this study chopped leaves of tropical tree species (5 N-fixing species, 5 non-N-fixing species and combinations of 5 N-fixing with a non-N-fixing species) were incorporated in soil to evaluate its effects on wheat biological productivity (including grain yield, GYIELD) under dryland conditions. High quality leaves of N-fixing tree species (e.g. Dalbergia sissoo, Cassia fistula and Prosopis cineraria) had lower carbon/nitrogen (C/N), lignin/nitrogen (LIG/N), polyphenol/nitrogen (PPL/N) and lignin+polyphenol /nitrogen (LIG+PPL/N) ratios than low quality leaves of non-N-fixing species. Combination treatments had intermediate values of different parameters. Application of high quality leaves caused greater increases in wheat productivity and yield than other species. By the application of leaves of N-fixing trees, on average, wheat yield increased 160% relative to the control (no addition of leaves), and when combined with non-N-fixing Terminalia chebula leaves the yield increased 108%. Mean total net productivity (TNP) with N-fixing species treatments, exceeded mean TNP with non-N-fixing species and combination treatments by 50% and 28%, respectively. Multivariate regressions indicated that nitrogen (N) concentration in leaves (main nutrient), interacting with lignin (LIG) and polyphenol (PPL) concentrations, explained 79%–86% of variability in productivity parameters and yield. Strong correlation between LIG+PPL/N ratio of leaves with GYIELD of wheat crop suggests that the ratio can be used as a reliable index for mass screening of multipurpose tree species for use as soil amendments especially in dryland agriculture. Direct application of high quality N-fixing tree species leaves (especially D. sissoo, C fistula and P. cineraria), an uncommon practice in dry tropics in India, may serve as a short-term option for rapid enhancement of wheat productivity and soil fertility.