Simultaneous Extraction of Phosphorus, Potassium, Calcium and Magnesium from Soils and Potassium Recommendations for Crops in Southern Brazil

Simultaneous multi-element extraction has been increasing worldwide to improve soil laboratory testing quality and efficiency. This study sought to investigate the applicability of the Mehlich-1, Mehlich-3, and resin methods for simultaneous extraction of soil available P, K, Ca, and Mg as well as the effect of using conversion equations on nutrient recommendations for crops. Topsoil （0-20 cm） samples were taken from the most representative soil types used for crop production in southern Brazil with a wide range of chemical, physical, and mineralogical properties. Soil P, K, Ca, and Mg were simultaneously extracted using 1.0 mol L-1 KCl, Mehlich-1 and Mehlich-3 solutions, and membrane resin. The amounts of P extracted with the Mehlich-1 method were, on average, 50% lower than those extracted with the resin and Mehlich-3 methods. However, the resin method extracted the lowest amounts of K, Ca, and Mg. The use of conversion equations was suitable and it did not affect negatively the K recommendations for crops grown on soils of southern Brazil.