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 accessio ns of Sesbania species and two accessions of Leucaena species were eva luated in a 5-week laboratory incubation. Leaves of these leguminous t rees, 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 relativ e to the soil (control). Nitrogen in sesbania leaves was mineralized m ore rapidly than that in leucaena leaves; one sesbania accession relea sed as much N as that released from urea fertilizer applied at an equi valent rate of 60 kg N ha(-1). Mineralizable N ranged from 15 to 53% o f leaf N and it was negatively correlated with hemicellulose content a nd hemicellulose-to-N ratio. The results indicate that additional N an d P may be required if these leaves are used as sources of nutrients f or crops. In acid soils low in Ca, additional Ca may also be required. (C) 1998 Elsevier Science Ltd. All rights reserved.