Over the course of 2007-2015, the department of the irrigated agriculture had been conducting research in the area of the Ingulets irrigation system on the experimental fields of the Institute of Irrigated Agriculture of the National Academy of Agrarian Sciences of Ukraine (NAAS), which were established in 1996, with the aim to develop and scientifically substantiate agroecological and technological methods for crop rotations on the irrigated lands of the Southern Steppe of Ukraine that will ensure soil fertility, increase crop productivity, economic and energetic efficiency. In 2007-2010, studies were conducted to substantiate the systems of basic tillage using different ploughing tools. The 4-field grain-row crop rotation 1 included winter wheat with post-harvest cultivation of millet, corn, soybeans and spring rape. Five studied systems of basic tillage differed in methods, techniques and the depth of soil loosening. In 2011-2015, grain-row crop rotation 2 entailed soybeans, instead of spring rape seed, and winter barley with post-harvest cultivation of millet, instead of winter wheat. Five studied systems of basic tillage differed in the depth of soil loosening and non-renewable energy costs for their implementation. Experiments were performed under conditions of two organo-mineral fertilizer systems using by-products of crop rotation, fertilizer application in doses of N75P60; N97, 5P60 and inoculation of soybeans with microbial compounds. Following crop rotations 1 and 2, a decrease in humus content within the 0-40 cm soil layer to the level of 1976, 110.2-114.4 t/ha, was observed. To prevent further decline in humus content, an optimization model was developed by capping specific weight of soybeans in short-term crop rotation 25%, stubble plowing the stem and leaf mass of crops as well as applying fertilizer quantities corresponding to the expected yields. With the help of mathematical modelling, it was determined that the retention of post-harvest plant remains in soil and the application of nitrogen and phosphorus fertilizers increased humus content in soil used for growing rape by 0.3%, winter wheat – by 0.7%, and corn – by 0.9%.

Efficient water management in agriculture is an important part of the general programme on water resources preservation. This study is devoted to the determination of the effects of soil processing system and mineral fertilization on the water use efficiency and productivity of grain corn (Zea mays Linnaeus, 1753). The trials were conducted in 2017–2018 on irrigated land in the South of Ukraine. The field experiments were carried out on the experimental plots of the Institute of Irrigated Agriculture of the NAAS in four replications. We studied the following agrotechnological parameters and their combinations: Factor A – primary tillage type and depth within different tillage systems in the short crop rotation (grain corn – grain sorghum – winter wheat – soybean); Factor B – application rates of mineral fertilizers (N0P0, N120P60, N180P60). We established that the highest yield of grain accompanied by the best water use efficiency was provided by the cultivation technology with disk cultivator tillage on the depth of 8–10 cm within the differentiated tillage system in the crop rotation under the maximum nutritive background of N180P60. This agrotechnological variant resulted in a corn grain yield of 14.51 and 14.59 t/ha in 2017 and 2018 years of the study, respectively. The coefficient of water use efficiency, which is the relation of the water used by the crop to the yield, in this variant was the lowest – 39.6 and 42.0 mm/t in 2017 and 2018, respectively, which indicates the optimum response of corn grain to watering. The worst indexes of water use efficiency and corn productivity were determined in the experimental variant with disk cultivator tillage on the depth of 12–14 cm within the subsoil tillage system within the crop rotation under non-fertilized conditions. We determined that strengthening of the crop nutrition under the rational tillage system in crop rotation is helpful in optimization of the crop water use in the irrigated conditions of the South of Ukraine, which is very important in the current conditions of freshwater scarcity.

In the article the brought results over of experimental researches of influence of different methods and depth of soil basic tillage and doses of mineral fertilization on agrophysical properties and productivity of soybean. A purpose of researches is establishment of the most effective methods of soil basic tillage and doses of application of mineral fertilizers at growing of soybean in row croprotation on the irrigation of south of Ukraine and their influence on a height and development of plants, forming of harvest and quality of seed. During an experiment used the field, in-gravimetric, visual, laboratory, calculation-comparative, mathematically-statistical methods with the use of confessedly methods and methodical recommendations. For determination of efficiency of action of soil basic tillage and doses of fertilizers on the productivity of soybean five variants of methods of basic tillage were stopped up and three variants of fertilizer systems: organic and two organo-mineral with doses bringing of mineral fertilizers - N30P60, N60P60 on a background of post harvesting bits and pieces of cultures of crop rotation and optimal mode of irrigation. Results. The changes of agrophysical properties happened under act of the systems of soil basic tillage, nourishing mode, that stipulated creation of different terms for a height and development of culture and forming of harvest. The productivity of seed of soybean at plowing on a 25-27 cm averaged for five years on a background the dose of fertilizers of N60P60 of 4,22 t/ha. At the combined tillage which united disk loosening on a 14-16 cm with slotting on a depth a 38-40 cm, 4,12 t/ha of seed of soybean is got in the system of differentiated-1 soil tillage. On the average on a factor B (system of fertilizer), the productivity of seed of soybean at organic system of fertilize made 2,38 t/ha. Bringing of dose N30P60 assisted the height of harvest on 0,84 t/ha, and N60P60 on 1,39 t/ha, or on 35,2 and 58,4% accordingly. Conclusion. In the short row crop rotation on the irrigated lands of south of Ukraine the most favorable terms for a height, development and forming of harvest of soybean on dark-chestnut soils are created in the systems of plowing basic soil tillage with the turn of layer or differentiated- 1 tillage with the deep loosening under soybean or shallow on a background slotting on a depth a 38-40 cm under a previous culture.

Малярчук М.П.-доктор сільськогосподарських наук, старший науковий співробітник https://orcid.org0000-0002-0150-6121 Інститут зрошуваного землеробства Національної академії аграрних наук України Томницький А.В.-кандидат сільськогосподарських наук https://orcid.org0000-0002-7820-4383 Інститут зрошуваного землеробства Національної академії аграрних наук України Лужанський І.Ю.-науковий співробітник https://orcid.org0000-0002-3832-6829 Інститут зрошуваного землеробства Національної академії аграрних наук України

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