Comparison of methods evaluating the plant available potassium content in soils of different types and potassium levels

Abstract

The amount and quality of clay minerals in Hungarian soils show considerable differences. In relation to this, in long‐term multi‐location field experiments, different levels of K supply have developed even when fertilized at the same K fertilizer rate. In an incubation experiment (4 weeks at constant temperature and moisture), carried out with the soil samples taken from several sites at these fertilization field trials which were different in their clay content and K levels, changes in the plant available K content in these soils were studied. A high constant dose of K fertilizer was applied on every soil type. Two extraction procedures were used for estimating plant available K content of soils, AL‐soluble (NH4‐lactate, pH 3.7) and NH4‐acetate (pH 7.0), were compared based on the obtained exchangeable amounts of K. As a consequence of the high K dose applied at the beginning of the incubation experiment, plant available K levels measured by the two extraction procedures were significantly different. However, a very close linear relationship were found between the values obtained with the two extractants.