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Role of root inputs from a dinitrogen-fixing tree in soil carbon and nitrogen sequestration in a tropical agroforestry system

Abstract : Agroforestry is often mentioned as a suitable technology for land rehabilitation in the tropics and for mitigation of climate change because this land-use favours nutrient recycling and C sequestration. The aim of this work was to estimate soil C sequestration in a 12-year-old tropical silvopastoral system composed of a legume tree (Gliricidia sepium) and a C4 fodder grass (Dichanthium aristatum), and to link it with tree root biomass and N status in the soil. The site was under cut-and-carry management, i.e. tree pruning residues and cut grass were removed from the field and fed to stabled animals elsewhere. Thus, main sources for tree C and N inputs were root activity and turnover. Organic C derived from the trees and tree root biomass were determined based on natural 13C abundance. For the 0-0.2 m soil layer, the biomass of tree roots <2 mm diameter was 2.4 Mg/ha when the trees were pruned every 6 months (SS6), and 0.6 Mg/ha when pruned every 2 months (SS2). Both C (R2 = 0.39, P < 0.05) and N (R2 = 0.82, P < 0.05) sequestration were correlated with tree root biomass. The trees and grass contributed 18 and 8 MgC/ha to soil, respectively, over the 12-year experiment in SS6. The net increase of 2.5 MgN/ha in soil, originating from the trees, contributed to the net soil C sequestration. In SS2, trees contributed 16 Mg C/ha to soil over 12 years, but grass-derived C was reduced by 2 Mg C/ha because of the small amount of grass litter. The increase of 1.7 Mg N/
Keywords : VERTOSOL TREE PRUNING
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Jorge Sierra, Pekka Nygren. Role of root inputs from a dinitrogen-fixing tree in soil carbon and nitrogen sequestration in a tropical agroforestry system. Australian Journal of Soil Research, CSIRO Publishing, 2005, 43 (5), pp.667-675. ⟨10.1071/SR04167⟩. ⟨hal-02678594⟩

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