8 research outputs found

    Carbon storage and DNA absorption in allophanic soils and paleosols

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    Andisols and andic paleosols dominated by the nanocrystalline mineral allophane sequester large amounts of carbon (C), attributable mainly to its chemical bonding with charged hydroxyl groups on the surface of allophane together with its physical protection in nanopores within and between allophane nanoaggregates. C near-edge X-ray absorption fine structure (NEXAFS) spectra for a New Zealand Andisol (Tirau series) showed that the organic matter (OM) mainly comprises quinonic, aromatic, aliphatic, and carboxylic C. In different buried horizons from several other Andisols, C contents varied but the C species were similar, attributable to pedogenic processes operating during developmental upbuilding, downward leaching, or both. The presence of OM in natural allophanic soils weakened the adsorption of DNA on clay; an adsorption isotherm experiment involving humic acid (HA) showed that HA-free synthetic allophane adsorbed seven times more DNA than HA-rich synthetic allophane. Phosphorus X-ray absorption near-edge structure (XANES) spectra for salmonsperm DNA and DNA-clay complexes indicated that DNA was bound to the allophane clay through the phosphate group, but it is not clear if DNA was chemically bound to the surface of the allophane or to OM, or both. We plan more experiments to investigate interactions among DNA, allophane (natural and synthetic), and OM. Because DNA shows a high affinity to allophane, we are studying the potential to reconstruct late Quaternary palaeoenvironments by attempting to extract and characterise ancient DNA from allophanic paleosol

    Soil Phosphorus Management in Organic Cropping Systems: From Current Practices to Avenues for a More Efficient Use of P Resources

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    Phosphorus (P) is a major nutrient for all living organisms and a key production factor in agriculture. In crop production, it is usually supplied to soils through fertilisers or recycled manure and compost. Organic production guidelines ban the use of highly soluble, manufactured P fertilisers and, thus, recommend recycling P from livestock manure and compost. In this chapter, after an overview of P dynamics in soils, we explore the consequences of such guidelines in terms of field- and farm-gate P budget, soil P availability and crop productivity. Moreover, we propose some avenues for the more effective use of P resources, ranging from rhizosphere-based processes (e.g., soil microorganism manipulation), genotype selection and cropping practices (e.g., intercropping), to farming system design (e.g., a combination of crops and animals at the farm scale). Finally, the potential benefits of these options are compared with respect to soil P status, field- and farm-P budgets
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