Soil supply with magnesium and the content of magnesium in the above-ground mass of young rye plants

The relationships between nutritive conditions of soils and magnesium content in plants were studied under controlled conditions of cultivation of the testing crop in climabox. The aim of this study was to specify more accurate an appropriate soil supply with magnesium. The collection of 19 soils was obtained from the topsoil of routine production plots of outstanding agricultural enterprises in the region where an attention was paid to the soil supply with potassium in relationship to magnesium over longer period of lime. To evaluate nutritive conditions of soils, three soil tests were used: Mehlich 2, KVK-UF and concentration of nutrients in soil solution. Availability of Magnesium for plants was assessed on the basis of analysis of above-ground mass of 14-day rye plants. The correlations found between the conditions of soil supply 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 magnesium in soil solution (Fig. 3). Despite the significant dependences were found in soil tests Mehlich 2 and KVK-UF, the use of the given relationships for the needs of optimization of soil supply with magnesium was very small due to a large variability (Figs 1 and 2) in practically 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 procedure could be caused by a marked acidity of extraction solution Mehlich 2 which releases unavailable forms of magnesium for plants, e.g. precipitates of dolomite character. Much closer correlations between soil tests and magnesium in plant were obtained when soil supply was expressed 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 ratio Mg/K would exceed 0.8; 0.7 and 0.6; gradually For the methods Mehlich 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 magnesium as the percentage of CEC saturation by equivalents of magnesium (Fig. 7). Variance of correlation field on the side of higher Mg content in plant was found in soils (5, 6, 7 and 16) which were characterized by lower content of potassium. The variance on the other side of the correlation field was associated with higher soil supply with potassium in relationship to CEC value (soils 15 and 17). It can be assumed from these results that under the condition of adequate supply with potassium the degree of saturation of adsorption complex by magnesium could 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 relationship between the soil test and the content of magnesium in the above-ground mass of young rye plants occurred when deviations in soil supply 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 successful without previous optimization of potassium in soil.