Effectiveness of agroecological practices in irrigated crop rotations in southern Ukraine

Abstract

The conservation and improvement of soil fertility and its ameliorative condition in field crop rotations on irrigated lands in Ukraine depends on the availability of organic matter, postharvest (leaf, stem and root) residues, green manure and dung, which are energy material for microbiological processes, nutrient regime formation and humus accumulation in the soil. Organic matter is the most important part of the soil, its role in the processes of soil and fertility formation is very important and multifaceted. The analysis of literary sources shows that among the agronomic practices the influence of fertilization and soil tillage systems on the dynamics of organic matter accumulation has not been sufficiently investigated. In this connection, there is an increased interest in further research on the trends in the processes of mineralization and humification, as well as on the pace of transformation and redistribution of organic matter under different fertilization systems and basic soil tillage and productivity formation in field crop rotations on irrigated lands.

The aim of the study was to provide scientific substantiation of the optimal parameters of the methods and depth of basic tillage of dark chestnut soils for agricultural crops under different systems of basic cultivation and fertilization in the irrigated row crop rotation. The research objective was to determine humus status, soil nutrient regime and productivity of agricultural crops under different rates of mineral fertilizers against the background of burying leaves, stems and roots of agricultural crops of the rotation using implements with a different design of the working parts.

The investigations were carried out in the stationary experiment of the irrigated agriculture department of the Institute of Irrigated Agriculture of the National Academy of Agrarian Sciences of Ukraine in 2010-2018 in a 4-field row crop rotation under irrigation in the operation zone of the Ingulets irrigation system. The crop rotation included grain corn, soybeans, winter wheat and grain sorghum. The soil of the experimental field is dark chestnut medium loam with low nitrate availability and medium availability of mobile phosphorus and exchangeable potassium. Humus content in the 0-40 cm-layer is 2.15%.

At the initiation stage of the experiment we used the following soil-cultivating implements: mounted bottom plow ПЛН -5-35, deep tillage chisel ЧГ-40-02, light trailed disc harrow БДЛП-4 and disc-chisel harrow БДВП-3.0-01. We seeded zoned varieties and hybrids of agricultural crops and applied growing technologies generally recognized for irrigated conditions. The irrigation regime ensured keeping up the pre-irrigation soil moisture threshold for crop rotation crops at a level of 70% LMHC (lowest moisture holding capacity) in the 0-50-cm soil layer.

During the experiment, we used field, quantitative and weight, visual, laboratory, comparative calculation, mathematical-statistical methods as well as methods and methodological recommendations widely recognized in Ukraine. Humus balance was calculated using linear regression equations for determining the mass of plant residues per yield of the main products developed by the scientists of the National scientific center Institute of Soil Science and Agrochemistry of NAASU.

The estimation of humus formation from stubble residues burried in the soil under different systems of basic tillage and fertilization background shows that a negative balance of humus is observed at the unfertilized background under all systems of basic tillage. At the same time, the highest negative indicators were under mouldboardless single-depth shallow cultivation and amounted to 0.35 t / ha, whereas under differentiated (option 1) treatment with soil slitting at a depth of 38-40 cm once per rotation they were the lowest - 0.16 t / ha. Against the fertilized background (N_82.5P₆₀ per hectar), there was recorded an increase in humus content under all systems of basic soil tillage. At the same time, in the variant of differentiated-1 basic soil tillage, an average annual estimated humus content increment reached +0.66 t/hа, while under multi-depth mouldboard (control) cultivation it was lower and made up +0.62 t/hа.

The application of differentiated (option 2) and multi-depth and single-depth shallow mouldboardless systems of basic soil cultivation (variants 5, 2, 3) under the organic and two organo-mineral fertilization systems led to a significant decrease in crop yield, especially of row crops, as well as to lower productivity of the crop rotation as a whole. Shallow (12-14 cm) disk loosening in the system of a long-term application of single-depth mouldboardless tillage against the background of the organic fertilization system led to the formation of the lowest crop rotation yields.

The application of mineral fertilizers at a rate of N₁₂₀P₆₀ against the background of postharvest residues under differentiated (option 1) system of basic tillage provided the highest crop yield of the rotation. In this case, grain corn yield was 14.82 t/ha, productivity of soybeans was 4.31 t/ha, the yielding capacity of winter wheat amounted to 6.90 t/ha, and that of grain sorghum reached 7.70 t/ha, the productivity of the crop rotation being 8.43 t / ha, which is 3.2% higher than the control. Only soybean crops brought a yield 0.7% lower than the control. A positive humus balance was also observed after the application of N₁₂₀P₆₀per hectare of the crop rotation area.

Thus, in row crop rotations on irrigated lands in the southern part of the Steppe zone it is expedient to apply organo-mineral fertilization systems with the use of postharvest residues of agricultural crops as a fertilizer, combined with mineral fertilizers at a rate of N₁₂₀P₆₀ at the background of a multi-depth system of basic tillage with plowing up and differentiated (option 1) cultivation with one soil slitting per rotation, which creates favorable nutrient and water regimes of the soil and promotes the formation of crop rotation productivity at a level of 8.17 - 8.43 tons / ha of grain.