The recent deterioration of the ecological condition of agricultural lands, the tendency of reducing soil fertility, and the production of plant products, mostly of low quality, necessitate an understanding of the role of trace elements in the process of plant formation. The content of trace elements in soils affects the efficiency of absorption of basic nutrients by plants. Deficiency of iron, manganese and zinc reduces the supply of nitrogen to plants. Copper and calcium promote the absorption of phosphorus by plants, but excess of iron inhibits it. Excess of copper and molybdenum reduces the transfer of potassium to plants. Due to high yields of agricultural crops, a significant amount of trace elements is removed from the soil, so the introduction of the optimal amount of trace elements against the background of high agricultural technology is an additional measure to increase the yields and quality of agricultural products. Heavy metals are an important environmental factor, which, on the one hand, is necessary for living organisms, and on the other (with increasing concentration of these elements in the environment) constitutes a negative factor in their lives. The activities of industrial enterprises, car exhausts and other attributes of civilization, increase the content of heavy metals in soils and as a consequence negatively affect their quality. The term "heavy metals" is used for the metals with a specific gravity exceeding 5 g/cm 3 or an atomic number of more than 20. Among them, lead and cadmium are considered the most dangerous. Therefore, modeling the content of trace elements and heavy metals in the Steppe soils of Ukraine is an additional mechanism for quality control of agricultural land and, as a consequence, of obtaining quality products to ensure food security of the state.

The intensive development of industry generates a number of negative consequences, which leads to an ecological crisis. As a result, the soil on which plant products are grown is polluted by radionuclides, heavy metals, pesticides, and chemicals. That is why in the early 1960s, the alternative farming, which is also called biological, biodynamic or organic, began to develop in Europe. The movement for alternative farming is widely developing in industrialized countries with a high level of chemization of agriculture. Therefore, the proposed topic is extremely relevant in terms of rational nature use, ensuring the sustainable development of territories, as well as food security in Ukraine. The article deals with agroecological assessment of suitability of agricultural land of the Steppe Zone of Ukraine for ecological farming and bases on the modern data from the Kherson branch of the state institution "Institute of Soil Protection of Ukraine". Spatial modeling of the presence of nutrients in the steppe soil of Ukraine was made by the means of ArcGIS 10.1 product. Taking into account the obtained data and spatial modeling, the territories with soils of limited suitability for ecological farming occupy 67.2% (1194.5 thousand hectares) of the Kherson region, unsuitable soils are located on 16.7% (297.4 thousand hectares) of agricultural land of the Steppe Zone of Ukraine and suitable lands were detected on 16.1% (286.2 thousand hectares) of the territory of the studied lands. The conclusion was made that with the actual availability of lands occupied under ecological farming (4.3% or 75.9 thousand hectares), the territory of the Steppe Zone of Ukraine has a prime potential to increase the area under ecological farming by 4.2 times. Therefore, the article paid attention to ecological farming, taking into account the specifics of the content of trace elements in the steppe soils and their compliance with the methodology for determining whether soils belong to the categories of suitable, limited-suitability and unsuitable for ecological farming.

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Abstract-This paper reports the results obtained using the systemic basin approach, geoinformation, and neurotechnology for modeling and forecasting of the humus spatial inhomogeneity and content variations in the steppe and dry steppe zones (Kherson oblast, Ukraine). The general trend of such variations has been determined in the 0-40 cm layer for 42 years. The intensive use of irrigation and drainage activities in 1970-1989 resulted in a significant humus depletion by 0.36% on average (from 2.56% to 2.2%). The analysis in 4450 observation points has yielded a decrease in the variability, the rising polynomial dependence of the humus enrichment from the west to the east, and the logarithmic dependence from the south to the north. The neurotechnological modeling has made it possible to develop the artificial neural network for the spatiotemporal modeling of the humus content in the soils. The humus is predicted to be subject to the irreversible process of gradual depletion in the 0-40 layer until 2025 upon the use of the existing agrotechnologies: rainfed land by 0.01%/year and irrigated land by 0.03%/year. This result defines the territorial priorities of the regional policy and suggests the differentiated efficiency evaluation of the soil-protective unit of the farming systems.

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