EFFECT OF YEARS, FERTILIZATION AND GROWING REGIONS ON THE CONTENT AND FORMS OF POTASSIUM IN SOIL

The dynamics of potassium (K) in soil was investigated in long-term small-plot field trials at seven stations, where five combinations of fertilization were tested. The objective of the experiment was to estimate the effect of the weather conditions, type of growing region and increasing doses of fertilizers on the content of water soluble K (Sol-K), exchangeable K (Ex-K) and acid soluble K (Ac-K) in soils. The weather conditions had the strongest effect on the total variability of the Sol-K (34.9%), to a lesser extent on the variability of Ex-K (14.1%) and only negligibly on the Ac-K (0.3%). In the individual years of the experimental period, the content of water soluble and Ex-K was particularly affected, chiefly by the weather and due to different demands of crops for this nutrient (leguminous plants consume high amounts and cereals relatively low amounts of K). In fairly dry years (e.g. 1982), the level of potassium (Sol-K and Ex-K) in soil was higher than in years with precipitation above the average. The content of soluble and exchangeable K was positively influenced by the application of potassium fertilization (0.989, 0.994, respectively). Compared to the control, the content of Sol-K and Ex-K in the variant where the fertilizer dose was the highest increased by 69.3 and 55.3%, respectively. Potassium fertilization (compared to the control) raised the level of the Ac-K, but not significantly, also implying that the effect of fertilization on the total variability of the Ac-K (0.6%) was virtually none. The effect of the growing region on the total variability of the potassium content was higher wherever the potassium bonding to the the sorption soil complex was stronger. The differences between the average levels of Sol-K characterizing the growing regions were not statistically significant. The levels of Ex-K and Ac-K differed significantly in the sugar-beet growing region, where the reserve was more than 40% higher than in the potato growing region.