Leguminous trees pass on nitrogen to crops
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CTA. 1991. Leguminous trees pass on nitrogen to crops. Spore 33. CTA, Wageningen, The Netherlands.
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Some field studies show that there is improved nodulation on the roots of leguminous trees when they are growing close to nonnitrogen-fixing plants. Moreover this increased nodulation may mean that nitrogen is being transferred directly to the roots of the non-leguminous plants. This hypothesis was discussed at a meeting in Nairobi which was organized by the International Council for Research in Agroforestry (ICRAF) and the International Board for Soil Research and Management (IBSRAM). It may upset one of the criteria for selecting trees for intercropping: ensuring that the roots of the tree should grow deeper than those of the crop. Studies in a coffee plantation showed that the roots of the leguminous tree, Inga jinicuil, were concentrated around the trunks of coffee trees, within or just below the litter layer. In a mixed Casuarina-Eucalyptus plantation in S.E.China, Casuarina roots with abundant nodules were found to be growing amongst the Eucalyptus roots. More evidence has been found in Indonesia, and in Nigeria it has been found that the roots of Leucaena leucocephala were growing amongst cassava roots in an alley cropping system. In Senegal one observer was surprised to find that roots of Albizia lebbeck had travelled 15 metres to become intertwined with sorghum roots. ICRAF and IBSRAM are hoping that interest in this matter will be raised and that this will lead to further studies. Dr.M.van Noordwijk,Institute for Soil Fertility Research, Haren, THE NEDERLANDS
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