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Spatial and temporal variation of below-ground N transfer from a leguminous tree to an associated grass in an agroforestry system

Abstract : Nitrogen (N) transfer from leguminous trees can be a major N source for the associated crop in low-input agroforestry systems. The aim of this study was to identify the main climatic and soil factors controlling N transfer from the leguminous tree Gliricidia sepium (Jacq.) Walp to the associated grass Dichanthium aristatum (Poir.) C.E. Hubb, in a 16-year-old tropical agroforestry system. Nitrogen transfer was estimated using the natural 15N abundance method. Before tree pruning, total N transfer represented 57% of the N uptake of the grass, including 31% coming from N2 fixation. The spatial variation induced by the tree was well described by soil organic N content (ON). In this system, ON is an index of soil available N as well as of tree root density. Rainfall (R) and evapotranspiration (ETP) were the main climatic factors controlling N transfer. Multiple regression analysis indicated that R, ETP and ON explained 79% of the temporal and spatial variation of N transfer. Transferred N cannot be estimated after pruning because of the change in the isotopic signature of the soil N source. This was related to N release from root turnover. The results suggest that grass showed a preferential uptake of N coming from the tree, which could be due to a lower energy cost compared to obtaining absorbed N from the clayey soil used in this work.
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Submitted on : Sunday, May 31, 2020 - 1:18:40 PM
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David Daudin, Jorge Sierra. Spatial and temporal variation of below-ground N transfer from a leguminous tree to an associated grass in an agroforestry system. Agriculture, Ecosystems and Environment, Elsevier Masson, 2008, 126 (3-4), pp.275-280. ⟨10.1016/j.agee.2008.02.009⟩. ⟨hal-02668652⟩

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