SOIL SUPPLY WITH MAGNESIUM AND THE CONTEN T OF MAGNESIUM IN THE ABOVEGROUND MASS OF YOUNG RYE PLANTS

The relationships between nutritive conditions of soils and magnesium content in plants were studied under controlled conditions of cultivat ion of the testing crop in climabox. The aim of this study was to spec ify more accurate an appropriate soil supply with magnesium. The colle ction of 19 soils was obtained from the topsoil of routine production plots of outstanding agricultural enterprises in the region where an a ttention was paid to the soil supply with potassium in relationship to magnesium over longer period of lime. To evaluate nutritive condition s of soils, three soil tests were used: Mehlich 2, KVK-UF and concentr ation of nutrients in soil solution. Availability of Magnesium for pla nts was assessed on the basis of analysis of above-ground mass of 14-d ay rye plants. The correlations found between the conditions of soil s upply and magnesium and its intake by rye plants are given in Tab. III . Fully inappropriate close relationship between magnesium in soil and magnesium in plant was Found in the case of the concentration of magn esium in soil solution (Fig. 3). Despite the significant dependences w ere found in soil tests Mehlich 2 and KVK-UF, the use of the given rel ationships for the needs of optimization of soil supply with magnesium was very small due to a large variability (Figs 1 and 2) in practical ly important range of the content of magnesium in soil (130 to 300 mg Mg/kg). Worse properties in the Mehlich 2 method against the KVK-UF pr ocedure could be caused by a marked acidity of extraction solution Meh lich 2 which releases unavailable forms of magnesium for plants, e.g. precipitates of dolomite character. Much closer correlations between s oil tests and magnesium in plant were obtained when soil supply was ex pressed in the form of weight ratio Md/K (Figs 4 to 6). To provide the lower limit of adequate content of magnesium in plant, the weight rat io Mg/K would exceed 0.8; 0.7 and 0.6; gradually For the methods Mehli ch 2, KVK-UF and soil solution. For Full obtaining of high quality of mineral composition ratios Mg/K would be over 1.8. A part of the soil test KVK-UF is also determination of cation exchange capacity (CEC) of soil. Thus, it should express the condition of soil supply with magne sium as the percentage of CEC saturation by equivalents of magnesium ( Fig. 7). Variance of correlation field on the side of higher Mg conten t in plant was found in soils (5, 6, 7 and 16) which were characterize d by lower content of potassium. The variance on the other side of the correlation field was associated with higher soil supply with potassi um in relationship to CEC value (soils 15 and 17). It can be assumed f rom these results that under the condition of adequate supply with pot assium the degree of saturation of adsorption complex by magnesium cou ld be a major criterion of the soil supply with magnesium. In our case , the suitable range of saturation of adsorption complex by magnesium should be 8 to 17%. The most marked accuracy of closeness of the relat ionship between the soil test and the content of magnesium in the abov e-ground mass of young rye plants occurred when deviations in soil sup ply with potassium from predicted lower limit of optimum after KVK-UF were included in the Mg-test of soil. The procedure of calculation of parameters is given under Tab. III. The regression relationships found are in Figs 8 and 9. The results obtained indicate that the solution of the problem of appropriate soil supply with magnesium cannot be suc cessful without previous optimization of potassium in soil.