Increasing of soil fertility in the Southern Steppe subzone, as in Ukraine as a whole, is one of the most important fundamental problems of nowadays, the solution of which will ensure the long-term sustainable development and high productivity of agro-ecological systems while preserving agricultural agro landscapes and, above all, their soil cover. One of the main directions that contribute to the production of stably high crop yields in the Southern Steppe subzone is the optimization of the structure of the sown areas and the increase of the fertility of degraded soils. The specified problem is solved by means of long-term bean grasses and legumes-cereal grass mixtures or reforestation. In this regard, the Institute for Irrigated Agriculture of the National Academy of Sciences has conducted the long-term research on the selection of leguminous perennial grasses and legume grass mixtures, whose biological features have been most adapted to the natural and climatic conditions of the subzone of the Southern Steppe and contributed to the fixation of atmospheric nitrogen from the air. The creation of high-yield single-species crops of leguminous perennial grasses and binary legume grass mixtures increases the fodder base for animal husbandry, reduces the mineralization of humus in soils, improves their physical and physico-chemical properties and, above all, reduces the catastrophic impact of natural phenomena associated with regional climate changes.