s:1856:"TI Soil phosphorus movement and budget after 13 years of fertilized cultivation in the Amazon basin 
AU Beck, M.A. 
AU Sanchez, P.A.J. 
AB Agronomic studies on soil phosphorus dynamics have primarily focused on the plant-available inorganic P pool. However organic P and less labile inorganic pools can contribute significantly to plant P uptake. The objectives of this study were to determine the changes in inorganic and organic P pools of varying lability in and below the plowlayer after 13 years of continuous cultivation and fertilization on a Typic Paleudult in Yurimaguas Peru. The field experiment was established after slash and burn of a secondary forest and included non-fertilized and fertilized treatments. The yearly cropping pattern consisted of an upland rice (Oryza sativa)-corn (Zea mays)-soybean (Glycine max) rotation. A modified version of the Hedley et al. procedure was used to sequentially fractionate soil P into increasingly recalcitrant organic and inorganic pools. Plowlayer accumulation of the fertilizer P occurred in all P pools. The greatest increase was in the NaOH extractable inorganic P pool. In the non-fertilized plots the organic P decreased by 42%. Phosphorus fertilization resulted in significant movement of P below plowlayer. The accumulation occurred mostly in inorganic and organic P pools that are not quantified by traditional soil-P test methods. In fertilized plots sub-plowlayer total P increased by 90 μg g−1 (87%) while resin extractable P increased only 4 μg g−1. Phosphorus content of the organic P pools below the plowlayer increased by 24 μg g−1 (50%) in fertilized plots. The inclusion of less labile P pools in studies of P movement and the evaluation of P fertilizer residual values could lead to a better understanding of P dynamics and hence better management of P fertilization. 
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