Predicting Phosphorus Buffer Coefficients of Representative Maize Soils in Laos

Abstract

Maize is an important crop in the Lao Peoples Democratic Republic (Laos) with as much as 113,808 ha grown in 2006. Recent research indicates that nearly all soils growing maize are deficient in phosphorus. In order to quantify the phosphorus requirement using the phosphorus decision support system (PDSS), the most important factor in the PDSS algorithm is the phosphorus buffer coefficient (PBC), which reflects the reaction of the soil to P fertilizer. The PBC was studied in 15 upland soils using the Bray 2 (PBC_{Bray 2}) and Mehlich 1 (PBC_{Mehlich 1}) methods and the iron oxide impregnated filter paper or Pi test (PBC _{Pi test}) procedure. Multiple regression analysis was used to quantify the relationship between the PBC and some soil properties involved in the P-sorption process. The PBC_{Bray 2} and PBC_Mehlich1 results were significantly correlated at the 0.01 levoerlg wanitihc carbon and iron having an adjusted R2 of 0.79 and 0.86 determined by the citrate bicarbonate dithionite method and the amount of clay, respectively. Unlike the two chemical extractions, the PBCPi test result was significantly correlated at the 0.01 level with aluminum (determined by the method using ammonium oxalate at pH 3 in darkness), the percent clay and organic carbon with an adjusted R² of 0.80. However, the study suggested that the PBC should be estimated by the Mehlich 1 method, so that the model could more accurately predict the PBC.