DEKKERS, DORINE & PETER VAN DER WERFF.
Department of Crop Science, Ecological Agriculture Group, Haarweg 333, NL-6709 RZ, Wageningen, THE NETHERLANDS.
Effects of long-term phosphorus (P) application on Vesicular Arbuscular Mycorrhizal colonization was studied after a 10 years fertilizer free recovery period, following 23 years of P fertilizer applications of 0, 17.5 or 52.5 kg ha-1 year-1. During ripening mixed soil, root and plant samples were taken and analyzed. The highest fertilizer application was about double P crop extraction, and resulted in a measured increase of 23 % of P-total concentration in the soil. Total mycorrhizal (VAM) and arbuscular colonization (AC) (expressed in %) were negatively affected by the P application of 52.5 kg ha-1 year-1 after 10 and 11 years without fertilizer application. VAM % and AC % at levels of 0 and 17.5 kg ha-1 year-1 P application were significantly higher than at 52.5 kg ha-1 year-1. Former fertilizer application of 52.5 kg ha-1 year-1 increased cost benefit ratio of the symbiosis between VAM fungi and plants, herewith affecting their mutualistic functioning.