The present study aims to characterize the effect of the annual potassium variable rates fertilization (VRF) on the content of the soluble K, with this being investigated in both light and heavy soils. The study was performed between 2007 and 2013 in two separate areas differing in the soil texture classes. The initial levels of potassium determined in both experimental areas were classified as very high. The data obtained confirmed the positive effect of the variable fertilization techniques on the equalization of the K contents in the experimental fields, as determined by the decrease in the variance, standard deviation, and range of the elements content in both types of the soils studied. As assumed, the controlled withholding of fertilization applied in the early stages of the experiment resulted in a decrease of K content toward the preferred, medium to optimal, levels. In addition, we found that the progressive initiation of the potassium VRF on the experimental areas, to prevent an excessive decreases, resulted in earlier global adjustment of K contents in the light soils in contrast to the heavy ones, with the final spatial equalization being better in the latter, however.
 Hawkesford M., Horst W., Kichey T., Lambers H., Schjoerring J., Moller S.I. et al., Functions of Macronutrients, Elsevier, San Diego USA, 2012.
 Andrist-Rangel Y., Simonsson M., Andersson S., Öborn I., Hillier S., Mineralogical budgeting of potassium in soil: A basis for understanding standard measures of reserve potassium, J. Plant Nutr. Soil Sci., 2006, 169, 605-615.
 Fotyma M., Content of potassium in different forms in the soils of southeast Poland, Pol. J. Soil Sci., 2007, 40, 19-32.
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