Biological Processes and Phosphate E8
Werff, P. van der; Dekkers, D.
Department of Ecological Agriculture, Wageningen AgriculturalUniversity, NL 6709 RZ Wageningen
|Phosphorous cycles in agro-ecosystems are
dominated by biological and geochemical processes. The current inefficient use of
phosphorous in agriculture has a strong impact on the long term geological cycle because
of the increasing use of phosphorous apatite reserves and enhanced turnover to marine
phosphorous reserves. The higher the realized direct phosphate availability levels are,
the higher is the phosphate fixation and the bigger the environmental losses are. In our
research we are studying soil biological processes that play a role in phosphate uptake by
crops in fields with a low phosphate availability and a sufficient phosphorous reserve in
organic matter, as is normal in organic farming.
Direct availability of phosphate determines initial crop growth. During crop development in the growing season the importance of biological phosphorous transfer is increasing. In this respect the increase of available phosphate by the activities of earthworms, the production of organic acids by plant roots, the excretion of phosphatase enzymes by microorganisms and Arbuscular Mycorrhizal Fungi (AMF), the increased colonization of the soil by the hyphal network of AMF are important examples of biological processes which enhance phosphate uptake. Reserves in organic or Calcium linked phosphorous can be used efficiently. Biological processes can account for over 25% of phosphorous uptake. Lower phosphate availabilities may result in yields that are 5-15% below maximum yields. The total phosphorous efficiency can be increased with 20-25%. This enables global use of rock phosphates on a longer term and it minimizes environmental pollution and waste of phosphorous to inaccessible fixed phosphates. However, the described phenomena and processes are dependent on abolition of at least systemic fungicides, nematicides and in the soil active insecticides to sustain the necessary soil organisms. Reduced soil cultivation is also a prerequisite for soil faunal development. Hence the long term perspectives at sustainable phosphate management can best be fulfilled with organic agriculture.
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Dekkers, T. B. M. (1995): Effect of organic manure and earthworms on the colonization of indigenous AM Fungi and phosphate uptake of barley in an organic farm. In: Azcon-Aguillar, C. & Barea, J. M. (eds.) Proceedings of the fourth European Symposium on Mycorrhiza. Granada. p. 524-527
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