Nutrient harvesting-the tree-root safety net

The hypothesis that deep rooting trees intercept nutrients which have leached below the crop rooting zone and compete for nutrients less strongly than trees rooting mainly within the crop root zone was tested in a mixed alley-cropping system on an Ultisol in North Lampung, Sumatra by measuring uptake of 15N placed at varying soildepths. Gliricidia sepillm, with its predominantly shallow root system, competed strongly for N with the crop and took up little 15N from lower soil depths. In contrast Peltophorum dasyrrachis roots exhibited a higher nutrient uptake activity at lower soildepth thus providing an active ‘safety-net’. Root activity as well as root length density has to be taken into account when assessing the efficiency of the safety-net.i’rellnlnary modelling results using WaNuLCAS suggested that Peltophonlln roots inthe 40-60 cm soil layer could reduce leaching by 5-10% over the course of a maize crop cycle in the rainy season.

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