Assessment of Multielement Extractants for Prediction of Available Potassium in Thai Soils

Abstract

In many countries, the efficiency of Mehlich 3 and ammonium bicarbonate – DTPA (ABDTPA) has long been elucidated as multielement extractants for simultaneous measurement of nutrient elements including potassium (K) in soils. However, information on their efficiencies for assessing the
availability of K in Thai soils is still inadequate. This study was conducted to assess the efficiency of the two multielement extractants in predicting available K in some Thai soils. The relationships between the amounts of K extracted by Mehlich 3 and AB-DTPA with those extracted by NH₄OAc, the
conventional extraction method, widely used in soil testing laboratories in Thailand, and those taken up by corn was investigated. The results indicated that the amounts of K extracted by both Mehlich 3 and AB-DTPA were highly correlated to those extracted by NH4OAc (r = 0.969** and r = 0.894**, respectively) and those absorbed by corn (r = 0.930** and 0.902**, respectively). In addition, coefficient of determination (r²) for the relationship between amounts of K taken up by corn and extracted by the three extractants were 0.887 (NH₄OAc), 0.866 (Mehlich 3), and 0.813 (AB-DTPA). Therefore, Mehlich 3 and AB-DTPA can be effectively used for determining K availability status in Thai soils. Nevertheless, Mehlich 3 was identified to be better measurement extractant than AB-DTPA.