Abstract

FERNANDEZ LOPEZ, Carolina  and  MENDOZA, Rodolfo. Evaluation of phosphorus available by three methods in different soils and productive managements. Cienc. suelo [online]. 2008, vol.26, n.1, pp.13-27. ISSN 1850-2067.

Phosphorus is a nutrient with low soil solubility and mobility and may present limited availability for plant growth. One way to increase phosphorus availability in soil is by fertilization. Due to the variability in the evaluation of phosphorus availability in soil, the study was carried out with the following objectives: a) to compare two of the most common soil available P methods (Bray I and Olsen), and the iron oxide impregnated filter paper method (Strip); b) to evaluate which of the methods is better related to some plant variables under different managements and soil conditions. The soils selected from Corrientes Province were: 1) Entisol: natural soil as a control and cultivated with Citrus, 2) Alfisol: control and cultivated with rice, 3) Vertisol: control and cultivated with pastures. Physical and chemical soil properties indicated that soils from the same order differed in the textural composition, despite having similar chemical properties, suggesting that the differences among soils can be ascribed to cultivation. In addition, a greenhouse pot trial was conducted.Six soils were fertilized with eleven levels of P (0-200 mg P kg^-1) and then incubated during 25 days at 28 °C. After incubation, soil samples were analyzed for P by the Olsen, Bray I and Strip methods. Rye grass was grown in pots during 45 days and the shoot dry matter was harvested and its P content analyzed. The results obtained in this work suggest that the three studied methods of P availability in soils described adequately and significantly the relationship between extracted P and dry matter yield (R² between 0.35 for the Vertisol and 0.95, for the Entisol), % P (R² between 0.92 and 0.95) and absorbed P (R² between 0.93 and 0.96). Nevertheless, the adjustments were different between soils, extractants and crop managements, suggesting the existence of a three-way interaction that determines different results in the final value of P availability in soil. Finally, we can conclude that the simplest method may not be the one that is most positively related to dry matter production or the concentration of the P in plant tissue.

Keywords : Bray P; Olsen P; Strip P; Entisoll; Alfisoll; Vertisoll.

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