Forage tree legumes. III. Release of nitrogen from leaf, faeces and urine derived from Leucaena and Gliricidia leaf

Abstract

The role of tree legume leaf as a green manure in increasing the N status of soils has been widely recognized. An alternative to the direct application of leaf is the feeding of the leaf to animals and using the dung and urine as the N source. This experiment was undertaken to measure the release of N from dried leaf of Leucaena leucocophala cv. Cunningham and Gliricidia sepium and from the dung and urine from goats fed the same leaf. The residue materials were labelled with 15N and either incorporated into the soil or applied onto the surface. ISN released from the residues was measured over a 10-week period by extraction using a grass crop of Panicum maximum cv. Riversdale and measurement of mineral N in the soil. Highest recovery was 89.6% in the leucaena-derived urine incorporated treatment and lowest (< 10%) in the surface-applied faeces treatment of both species. 15N recovery in the grass indicated that leucaena leaf is more resistant to breakdown than gliricidia leaf. These data suggest that careful consideration should be given to the use of leaf litter as an N source. In situations where volatilization of N from excreta can be minimized, such as in cut-and-carry systems, the N economy of the system could be enhanced by including the animal in the N cycle.