Abstract

FERNANDEZ LOPEZ, Carolina; MENDOZA, Rodolfo  and  VAZQUEZ, Sara. Fractions of phosphorus in soils of Corrientes with citrus, rice and pasture production. Cienc. suelo [online]. 2006, vol.24, n.2, pp.161-168. ISSN 1850-2067.

The objectives of this study were to determine the phosphorus fractions in Entisolls, Alfisolls and Vertisolls and to analyze the effects of the production system employed (citrus, pasture and rice) on this fractionation. Three soils from fields that mainly contribute to the economy of Corrientes were selected. A simple random sampling of two treatments and five replicates was conducted in each soil order, each replicate were a composed samples from 0-15 cm depth. Samples were selected from: 1) Entisoll: native grassland vs. citrus field, 2) Alfisoll: native grassland vs. rice crop, 3) Vertisoll: native grassland vs. Setaria sp. pasture. The parameters analysed were: texture, pH, orgaic carbon, calcium, magnesium, carbonate, iron and aluminium in oxalate, available phosphorus (P Bray I) and phosphorus (P) fractionation by Hedley et al. (1982) Method modified by Sattell and Morris (1992). Total P was calculated as the total addition of each phosphorous fraction. The smallest total P detected was observed in Entisolls (71.46 mg P kg^-1soil), followed by Alfisolls (126,84 mgP kg^-1 soil) and Vertisolls (142.28 mgP kg^-1soil). The most predominant fraction of total P was the organic phosphorus in sodium hydroxide (53%, 54% y 48% respectively for each order). Fertilization decreased available P, but increased moderately labile and resistant phosphorus fractions in Entisolls. Only P fraction from inorganic phosphorus in microaggregates and residual organic in Alfisolls were increased under rice crop production. The implantation of Setaria sp. with fertilization in Vertisols raised the occluded organic phosphorus in the microaggregate fraction.

Keywords : Forms of P; Phosphate fertilization; Entisol; Alfisol; Vertisol.

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