Estimativa da vulnerabilidade à perda de fósforo por diferentes versões do método do índice de fósforo

Abstract

Identification of areas with potential contamination of water courses by phosphorus (P) can be carried out through methodologies such as the Phosphorus Index (IP). However, the validation of the best model is necessary for the construction of risk scenarios for environmental contamination. The objective of this work was to verify the adjustment of three IP versions in the estimation of the vulnerability of the potential loss of P in a rural river basin. The basin area is 79.5 ha and is located in the municipality of Júlio de Castilhos, Rio Grande do Sul, Brazil. Three versions of IP were used to estimate the transfer of P to water courses. The validation of the models was made based on the actual P results in the soil and by the measured in the analysis of the runoff in the watershed exudation. Subsequently, a scenario was simulated where P levels in the soil were adequate to obtain high yields. The three versions of the IP presented variations in the estimate of the potential loss of phosphorus. The actual and estimated data showed low loss of soil and P and was attributed to the soft relief to the slightly undulated, the presence of wetlands in the convergent slopes, to the soil management and to the low level of available P. The Alabama IP version presented a better estimation of the vulnerability of soil P loss to watercourses. However, the IP version of Nebraska more realistically predicts the transfer of P to aquatic systems when using doses of P suitable for high yields.