Shevchuk O. Agrochemical efficiency of biogas production by-products on grey forest soil of the Right-Bank Forest-Steppe of Ukraine

Practical recommendations for the digestate use have been developed. It has been established that early spring fertilization of winter wheat with liquid digestate at a dose of 10 m3/ha is advisable which will replace the application of synthetic nitrogen fertilizers with a total dose of 109 kg/ha of active ingredient in spring and at the stage of BBCH 28-29. Under this fertilization scenario, grain yield can be 7.64-8.68 t/ha with a protein content of 10.7-11.4% depending on weather conditions. Different combinations of digestate with mineral fertilizers were evaluated compared to the traditional fertilizer application system and the effectiveness of its application at a dose of 20 m3/ha or in combination with aqueous ammonia in a nitrogen ratio of 1:1 at a dose of N200 has been established. The doses of nitrogen application with different fertilizer products in feeding and the development stage of winter wheat plants significantly affect the nitrogen content of mineral compounds in the soil layer 0-40 cm. Fertilization with digestate, compared to nitrogen fertilizers, improves the nitrogen regime of the soil at the end of the winter wheat growing season. Fertilization of winter wheat with nitrogen fertilizers (109 kg/ha of active ingredient) and digestate provides an increase in yield of 0.60-2.4 t/ha or by 10-41% and decreases with an increase in the dose of digestate application from 10 to 20-30 m3/ha. At a digestate dose of 10 m3/ha, there is only a tendency to reduce grain yield compared to the production control (N109) by 0.31 t/ha or by 4%. Feeding winter wheat with digestate in spring at doses of more than 30 m3/ha does not contribute to a significant increase in winter wheat yield. At a dose of 30 m3/ha, a significant increase in grain yield is ensured - 0.78 t/ha or 15% compared to the control without fertilizing, but at the same time it is inferior to production control with fertilizing crops with nitrogen mineral fertilizers at a dose of 109 kg/ha of active ingredient. Increasing the digestate dose to 50 and 70 t/ha did not significantly change grain yield compared to absolute control. Early spring feeding of winter wheat with digestate at a dose of 10-30 m3/ha is not inferior in terms of its impact on grain quality indicators to the traditional system of fertilizing it with synthetic nitrogen fertilizers. With an increase in the digestate dose to 20 and 30 m3/ha, the protein yield per unit of sown area decreases by 16 and 42%, respectively, which is explained by a decrease in grain yield. Feeding winter wheat with digestate at a dose of 10 m3/ha provides an intensity of nitrogen balance of 61.0%, phosphorus - 168.4% and potassium - 200.5% which indicates the need for additional nitrogen application. At the same time, the utilization rate of nitrogen from digestate is 82.6%, phosphorus - 32.6%, and potassium - 77.4%, and decreases at a dose of 30 m3/ha to 13.9%, 4.8%, and 22.0%, respectively. Under different fertilizer systems, corn yield increases by 2.65-2.96 t/ha or by 46-51% compared to the yield in the control without fertilizers of 5.80 t/ha. When applying 10 m3/ha of digestate in combination with aqueous ammonia, there is a tendency to increase yield by 0.31 t/ha or by 12% compared to applying only digestate at a dose of 20 m3/ha. Application of digestate to corn at a dose of 20 m3/ha compared to the production control of 200 kg/ha in the form of aqueous ammonia does not significantly change grain quality indicators. At the same time, there is a tendency of improving the grain unit and its protein content. The most favorable balance of nitrogen, phosphorus and potassium in the soil, assuming that only corn grains are removed from the field - 68.0 kg/ha, 54.1 and 44.2 kg/ha, respectively, is formed by the fertilizer system Digestate 10 m3/ha+Nva and a total nitrogen dose of 200 kg/ha. The lowest digestate consumption for the formation of 1 ton of winter wheat grain (4.6 m3) is provided by its spring feeding at a dose of 10 m3/ha. At the same time, 1 m3 of digestate contributes to the formation of 216 kg of grain. The nitrogen fertilizer consumption for the formation of 1 ton of corn grain yield increase is 4% lower compared to the production control (N200 in the form of aqueous ammonia) when combining digestate and aqueous ammonia in the fertilizer system in a ratio of 1:1 by nitrogen. At the same time, the payback of nitrogen increases by 11% compared to its application in the form of digestate at a dose of 20 m3/ha. The use of digestate in the fertilization system of winter wheat and corn is economically viable and can replace expensive synthetic nitrogen fertilizers. In this respect, it is necessary to take into account, first of all, the costs of transporting digestate from the biogas plant to the field. The payback of 1 UAH of costs for different winter wheat fertilizer systems varies within 0.5-4.8 UAH and is the highest for feeding it with digestate at a dose of 10 m3/ha.