NITROGEN EMISSIONS IN EUCALYPTUS DEGLUPTA AND GMELINA ARBOREA HEDGEROW SYSTEMS IN THE UPLANDS OF SOUTHERN PHILIPPINES

摘要

Nitrogen oxide emissions from agricultural soils are the most important anthropogenic source of this gas. Agroforestry is a dynamic, ecologically-based, natural resource management system that, through the integration of trees and livestock in farm, diversifies and sustains smallholder production for increased social, economic and environmental benefits. In hedgerow systems designed to restore or maintain soil fertility, tree litter, crop residues and animal manure are used as green manure. Thus, these systems may serve as source of nitrogen oxides, the extent depending on the management practices and the component trees and crops of the system. Eucalyptus deglupta and Gmelina arborea are the two top ranking trees planted in the agroforestry farms in Claveria. Experimental plots were established in E. deglupta- and G. arborea- based hedgerow agroforestry systems to measure nitrogen oxide emissions from fertilization, tree litterfall and litter decomposition, maize residue incorporation and livestock manure. Results showed that crop residue incorporation and fertilizer application are the major sources of nitrogen inputs in these hedgerow systems. Animal manure and leaf are other sources of nitrogen inputs into the soil. Gmelina arborea has higher leaf litter fall and faster rate of decomposition than E. deglupta. The growth and biomass of maize in alley areas under E. deglupta hedgerows are higher than those grown under G. arborea hedgerows. Use of local values for N excretion factors will reduce uncertainties in the estimates of N excretion from animal manure.