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Soil phosphorus movement and budget after 13 years of fertilized cultivation in the Amazon basin

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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 g g1 (87%) while resin extractable P increased only 4 g g1. Phosphorus content of the organic P pools below the plowlayer increased by 24 g g1 (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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    Beck M A; Sanchez P A J




    cropping patterns, humid tropics, nutrient uptake, phosphorus, secondary forests, shifting cultivation, soil testing, fertilizer



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