As a result of the analysis on the studies carried out in different parts of the world it is established that plants can uptake magnesium even at 20-fold excess of calcium over magnesium without any shortage when the content of total magnesium in soil is sufficient. At the same time, magnesium uptake by plants can be under the impact of such competing ions as potassium, ammonium, and manganese. When transpiration increases, plants enhance the uptake of magnesium. Therefore sufficient supply of magnesium in the periods of peak uptake of the elements which provide crop formation, such as nitrogen, potassium, sulfur, is essential for realizing bio-potential of plants. Magnesium deficiency, which inhibits plant growth, can usually occur in light soil at low pH values and high content of potassium and (or) ammonium, when soil is lack of exchangeable magnesium. Excess content of magnesium can affect on plants when the ratio of magnesium to calcium is bigger than unity. The same ratio facilitates for negative soil properties: water permeability and hydraulic conductivity decrease; soil sealing forms; dispersion properties of sodium increase. The soils with high content of smectite (montmorillonite), such as ordinary chernozem, are the most susceptible to exchangeable magnesium predominance in soil exchangeable complex. Negative soil properties at higher magnesium content can be the result of organic matter content decreasing due to the absence of biological affinity with magnesium in soil profile.
Keywords: magnesium, magnesium shortage, magnesium excess, smectite, ordinary chernozem, organic matter.
