Predicting Phosphorus Buffer Coefficients of Some Representative Soils for Maize Production in Lao PDR by Three Soil Analysis Methods

Abstract

Phosphorus buffer coefficient (PBC) is one of the important factors in the phosphorus fertilizer recommendation prediction by the use of Phosphorus Decision Support System (PDSS) program. A study on PBC of 7 representative maize soils in Laos and one Thai soil was conducted. The PBC determination was done by mixing the soils with potassium dihydrogen phosphate (KH₂PO₄) at the rates of 0, 25, 50, 100 and 200 mg P kg^-1. All soil samples were kept in the incubator at 30 °C for two weeks. The extractable P was analyzed by three methods: Bray-2, Mehlich-1 and iron oxide-impregnated filter paper method or Pi-test. The results showed different PBC values of soils with different extractants. Multiple regression analysis was used to determine the relationship between the PBC and soil properties. It revealed that PBC_Bray-2 was correlated with percentage of clay content with adjR²=0.64 and PBC_Pi-test was correlated with percentage of clay content and ammonium oxalate extractable aluminum, with
adjR² =0.89. The soil properties were substituted in the two models to predict the PBC_Bray-2 and PBC_Pi-test, respectively. The predicted PBC was plotted against observed PBC to compare the prediction accuracy using soil properties by 1:1 line relationship. The result showed that the PBC should be estimated by Pitest for more accurate PBC prediction.