Scientific Journal of KubSAU

The article presents the results of the study on the magnesium mode of leached chernozem of Western Ciscaucasia at three rotation of grain-grass-tilled crop rotation. Magnesium in the soil is represented mainly by non-exchangeable form, the number of which is estimated at 90,18 and 91,29 % of gross reserves. Exchange forms of magnesium are 8,68 and 7,71 % respectively in arable and the subsurface layer. The share of water-soluble and organic forms account for less than 1 % - of 0.62 and 0.68 and 0.46 and 0.38% respectively. For three rotation 11-full rotation of gross stocks of magnesium in the soil in which crops were grown without fertilizers has decreased by 0.02 % (200 mg/kg), with fertilizers of 0.03 and 0.02 % (300 and 200 mg/kg). Intense magnesium has been leached from the topsoil. There was a change of the soil content of the forms of magnesium. In the rotation without fertilizer, the share of non-exchangeable magnesium in the General Fund item increased from baseline by 0.27 % in arable and 0.11% of the subsurface layer of soil that the absolute content decreased. The amount of water-soluble, exchangeable and organic magnesium of the soil decreased. Reducing the amount of water-soluble (0.05 and 0.06 %) and metabolic (0.18 and 0.02 %) of magnesium was due to its consumption of the plants. The proportion of magnesium organic part of the soil is reduced as a result of steadily declining yields, and, therefore, the amount of organic residues. In crop rotation, use of mineral fertilizers we have observed different behavior of magnesium compounds in the soil. The number of non-exchangeable magnesium decreased from baseline by 0.13 % in arable and 0,58 % of the subsurface layer of soil. The content of the exchange of magnesium increased respectively 0.43 and 0.41 %, water soluble - 0.13 and 0.10 %, and the organic part of the soil - 0.02 and 0.02 %

The contents of lead in soils are primarily determined by regional factors: the composition of parent rocks, relief, climate, vegetation. In recent years, these factors have increased the anthropogenic source of element. In order to assess its impact, requires knowledge of the natural, i.e., background lead levels, the so-called reference points, which can later be used to monitor changes occurring in the soil. Under background refers to the content of the element in soils at a great distance from the areas of receipt of contamination. Background content of lead in each type of soil depends mainly on composition of parent rocks. The correlation coefficient between the content of lead in parent rocks and soils, with the background contents is equal to 0,86±0,17 at p=0,95. For each soil type there are low variations in lead content due to the composition of parent rocks. Lead concentrations in the soils increased at the expense of its receipt from the atmosphere, irrigation water, drainage during mining, as a result of agricultural use, lead containing chemicals. Comparing the obtained results with existing currently permissible concentrations (APC, MPC) it is necessary to note that the lead content in leached chernozem soil after three rotations of the rotation may not cause any pathological changes or anomalies in the course of biological processes and lead to accumulation in the agricultural plants, and therefore may interfere with biological optimum

The content of selenium in the soils of various genetic types varies widely. Its amount is lower in soils formed on volcanic rocks. On average, it is 0.2-0.6 mg/kg. In the soils formed on sedimentary rocks, the content of selenium is often in the range of 4.5-5.0 mg/kg and depending on the conditions of formation it varies widely, sometimes reaching 100 mg/kg. Predominantly they are alkaline soils, selenium concentrations in the soil solution is 10-6 moles. The content of selenium in most soil types of the Russian Federation and CIS countries varies in the range of 0.01-1.0 mg/kg. Floodplain, chestnut soils, black soils and gray soils are more enriched (0.3 to 1.0 mg/kg), whereas sod-podzolic and sandy soils are relatively depleted (0,05-0,2 mg/kg). Systematic application of mineral fertilizers on the fields of crop rotation leads to a decrease in total content in the leached black soil. Fertilizers contribute to increased mobility of this element and more intensive involvement of it in the biological cycle

Chromium in soils is represented by the following forms of connections: 1) stationary; 2) strongly bound in the composition of primary and partially secondary clay minerals, with one and a half aluminum and iron hydroxides; 3) exchange bound on the surface of one-and-a-half oxides and clay minerals; 4) associated with organic matter of soils; 5) water-soluble compounds. The gross chromium content (70.1-78.3 mg/kg) in leached chernozem is well below clark soils of the world (100 mg/kg). The share of mobile, acid-soluble and acid-insoluble forms of the element compounds is 0.01, respectively; 7.09 and 92.9 % of its gross content. After three rotations of 11-full grain-grass-tillage crop rotation without mineral fertilizers, the chromium content in leached chernozem has not undergone significant changes, even to some extent there is a tendency of its reduction. This indicates the absence of serious natural sources of chromium in the soil. Scientifically-based system of fertilizers for agricultural crops does not lead to anthropogenic pollution of leached chernozem with chromium. The removal of this element with crop yields is compensated by its receipt in the form of ballast with mineral fertilizers