PHOSPHORUS IN THE PAMPEAN SEMIARID REGION OF ARGENTINA .1. BRAY AND ANIONIC-EXCHANGE RESIN EXTRACTABLE PHOSPHORUS

There is often a lack response of wheat to phosphorus (P) fertilization in the Pampean semi-arid area of Argentina. Consequently, the fate of fertilizer P in an entic Haplustoll soil was investigated under three production systems commonly practiced in that region. The following procedures were conducted: i) comparison and linear regession of the values of P obtained by Bray I (Pbray) versus the anionic exchange resin (Paer) procedure (Paer = 2.35 + 0.68 Pbray), ii) addition of different amounts of KH2PO4 to the Ap horizon, and after incubation at 25-degrees-C for 6 months, extraction of the Paer in order to establish an index of fertilizer availability F1 which was: F1 = -0.13, and iii) determination by X-ray diffractometry of the generated brushita (DCPD) in the incubated samples to which P was added. The decrease in labile P could explain the lack of wheat response to the P fertilization in certain years.