Opportunities for capture of deep soil nutrients

This paper discusses the mechanisms by which nutrients occur in deep layers which include downward leaching of mobile nutrients, biological breakdown of soil organic matter and chemical breakdown of minerals. Soil nutrients not accessible to annual crops can be extracted by perennials through two processes: (i) the retrieval of nutrients already present in layers below the effective extent of rooting of annual crops; and (ii) the interception of nutrients moving below or outside the rooting zone of annuals. Several agroecosystems with the potential for more efficient use of nutrient resources in deep soil are illustrated: (i) intercropping perennials and annuals for complementarity in resource use; (ii) incorporating annuals into underutilized zones of tree plantations; and (iii) mixing plant species for spatial complementarity. Finally, suggestions to prevent the accumulation of mobile nutrients (nitrate) in deep soil are provided, including research in Kenya demonstrating that phosphorus fertilizer application can reduce nitrate accumulation in deep soil during continuous cropping of maize

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