Nitrogen release from leaves of leguminous and nonleguminous tree species in sandy loam soil

Abstract

To decrease adverse environmental impacts of fertilizer N and to decrease input costs in agroecosystems, there is a renewed interest in using green manure to maintain soil fertility. Nitrogen mineralization from the leaves of two leguminous /Leucaena leucocephala (Lamb.) de Witt, and Acacia nilotica (Linn.) Willd. ex Del] and two nonleguminous (Azadirachta indica A. Jussieu and Melia azedarach L.) tree species was compared in a sandy loam soil (Typic Camborthids) at constant temperature (35°C) and moisture (‐0.03 MPa). The cumulative amounts of mineralized N from the leaves of four tree species increased with increasing incubation periods; however, the magnitude ofN mineralization decreased with an increase in the incubation period and the amount of tree leaves applied to the soil. Mineralization patterns of all four species were almost identical, but the mineralization rate differed markedly among leaf materials. At 100 mg of leaf material added per gram of soil, the amount of net mineralized N was of the order L. leucocephala (323 mg kg‐1 soil) > M. azedarach (315 mg kg‐1 soil) > A. indica (269 mg kg‐1 soil) > A. nilotica (70 mg kg‐1 soil). The nitrogen mineralization potentials (No) differed markedly among the four tree species. It ranged from 71 (A. nilotica) to 284 mg per kilogram of soil ( L. Leucocephala) at 25 mg of leaf material added per gram of soil, and from 82 to 332 mg per kilogram of soil at 100 mg of leaf material added per gram of soil for the same corresponding tree species. Irrespective of added leaf material concentrations, the mineralization potential ( No) of the leaves was also of the order L. Leucocephala > M. azedarach > A. indica > A. nilotica. The N mineralization rate constants (k) did not differ significantly among L. leucocephala, M. azedarach, and A. indica except between L. leucocephala and M. azedarach or A. indica at 25 mg of leaf material per grams of soil amendment but were significantly higher than those of A. nilotica at all concentrations of added leaf material. In this study the N content and C/N ratio were found to best describe N mineralization from both leguminous and nonleguminous tree species.