Mineralization of N, P, K, Ca and Mg from sesbania and leucaena leaves varying in chemical composition

The N.P.K. Ca and Mg release patterns of the leaves of four accessions of Sesbania species and two accessions of Leucaena species were evaluated in a 5-week laboratory incubation. Leaves of these leguminous trees, applied at an equivalent rate of 3 t dm ha-1, were significant sources of N, K and Mg, but insignificant sources of P and Ca relative to the soil (control). Nitrogen in sesbania leaves was mineralized more rapidly than that in leucaena leaves; one sesbania accession released as much N as that released from urea fertilizer applied at an equivalent rate of 60 kg N ha-1. Mineralizable N ranged from 15 to 53 percent leaf N and it was negatively correlated with hemicellulose content and hemicellulose-to-N ratio. The results indicate that additional N and P may be required if these leaves are used as sources of nutrients for crops. In acid soils low in Ca, additional Ca may also be required.