POTASSIUM RESERVE IN SOIL AND ITS UPTAKE BY BARLEY

The research was conducted with a set of 18 soils of different sites o f the Czech Republic. The soils were analayzed for characteristics of their potassium reserves (i.e. exchangeable potassium, including water -soluble potassium), potassium reserve and soil capacity for wet fixat ion of potassium, furthermore, for the value of exchangeable soil acid ity and cation exchangeable soil capacity (Tab. 1). Four-weeks persist ing vegetation trials were established with the set of soils under con trolled conditions of cultivation in climabox. Spring barley was a tes ting crop. The studies were concentrated on the finding the dependence between solid stage of soil; soil solution and the plant for the need s of specification of suitable reserves of different soils with potass ium. The relationships found between the solid stage of soil and soil solution are shown in Figs 1, 2 and 3. The closest relationship, suita ble to predict the concentration of potassium in the soil solution fro m current data of soil testing, was found after transformation of the values of exchangeable potassium into its equivalent representation in the value of cation exchangeable soil capacity. The lower closeness o f dependence of soil solution concentration was recorded with using th e ratio of potassium activity (K / square-root Ca + Mg). This dependen ce was, however, much closer than in the case of the value itself of e xchangeable potassium. The dependence found in the potassium content i n plant on its concentration in soil solution was low (Fig. 4). The cl osest dependence in potassium content in the plant was found in the si mple content of exchangeable potassium in soil. Any other adjustments of exchangeable potassium through other characteristics of soil supply with potassium (i.e. K concentration in soil solution, mobile reserve of potassium, potassium fixation through soil) did not improve the cl oseness of relationships. Functioning of two ways of defining the suit able soil reserve with potassium was tested as follows: a) physico-che mical approach based on the above-mentioned sorptive soil capacity and on the degree of its saturation with potassium; b) biological and che mical, according to the concept of nutrient efficiency index. A high d egree of dependence of potassium content in plant in both approaches, expressed in percentage of deviation from predicted optima of soil sup ply with potassium (Fig. 6). The results of trials document a good fun ctioning of both approaches of defining the suitable soil supply with potassium. Biologico-chemical approach brought up under control a mark ed anomaly in desorption capacity of potassium in soil 4. This indicat ed the necessity to classify the soils in the categories for the needs of correct definition of different levels of reserve optima of differ ent soils with potassium. The use of concept of potassium efficiency i ndex to define the suitable soil supply with potassium is in Fig. 7.