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Book of Abstracts

11th IFOAM
Scientific Conference
11-15 August 1996
Copenhagen, Denmark

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Subject index
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Extra Papers

Biological Processes and Phosphate E8

Werff, P. van der; Dekkers, D.

Department of Ecological Agriculture, Wageningen AgriculturalUniversity, NL 6709 RZ Wageningen

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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.

Werff, P. A. van der, Amelsvoort, P. A. M. van , Marinissen, J. C. Y & Frissen, P. (1995): The influence of earthworms and Vesicular-Arbuscular Mycorrhiza on the availability of phosphate in ecological arable farming. Acta Zoologica Fennica, 196, 41-44

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

Sharpley, A. N. & Withers, P. J. (1994): The environmentally-sound management of agricultural phosphorus. Fertilizer Research, 39, 133-146.