Potassium availability to flooded rice in lowland soils

ABSTRACT Non-exchangeable potassium (K) forms are not estimated by usual methods of soil K availability, like Mehlich-1, but they can contribute to K nutrition of flooded rice. This study aimed at evaluating K forms in lowland soils by different chemical methods and associate them to K absorption by flooded rice. Fourteen lowland soils cultivated with flooded rice (IRGA 417 cultivar) were sampled and used in a greenhouse experiment. The K forms in the soil samples were extracted before and after rice cultivation by using calcium chlorite, Mehlich-1, sodium tetra phenyl borate (NaTFB) and fluorite acid. The K uptake was measured in rice shoots. There was a wide variation in K forms among the lowland soils. The variation in the amount of K extracted by using the Mehlich-1 method does not explain the K absorption by irrigated rice plants in every soil. The NaTFB method was more sensitive to evaluate K availability in lowland soils cultivated with flooded rice plants.