Potassium fixation in Portuguese soils

Abstract

In Portugal, since the 1930s, the results of experimentation on potassium fertilization have frequently caused perplexity among researchers. In such cases, where clear responses to K were expected due to low K concentrations in the soils, they did not occur or were very slow in manifesting themselves, particularly in the south of the country. In this review paper a retrospective of the existing experimentation was carried out where the inefficacy of K fertilization was evident. In addition, an inventory of soil types was made where evidence of K fixation had been most often detected, either through experimental trials or through laboratory tests. The laboratory data refer to the determination of soil K fixation capacity. With regard to K fixation, in addition to the identification of the K-fixing soils, the propitious factors for fixation of this nutrient are discussed, highlighting the mineralogical composition of soils in the clay, silt and fine sand fractions. Finally, based on the studies already carried out, some strategies to be followed in potassium fertilization were proposed.