Weediness of soybean (Glycine max) crops under different systems of main tillage and green manuring

Study of the impact of traditional and zero-tillage systems and organo-mineral fertilization systems with the use of green manure crops in intermediate post-harvest sowings on crop weediness and soybean yield when growing it in an irrigated short-rotation crop rotation of the Southern Steppe of Ukraine. The research was carried out on the basis of a stationary experiment laid out in the fields of the Askanian State Agricultural Research Station Institute of Irrigated Agriculture of NAAS in the area of operation of the Kakhovka irrigation system. The scheme of the experiment included three variants of the main tillage and four variants of fertilization with post-harvest sowings of green manure of buckwheat (Fagopyrum esculentum Moench.), phacelia (Pracelia tanacetifolia Benth.) and white one-year-old sweet clover (Melilotus albus). Field, quantitative-weight, calculation-comparative, and mathematical-statistical methods were used. The average number of weeds in soybean crops when plowing was the lowest and was 28.5 pcs/m2. With zero tillage, both in the second year and longterm use, an increase in the weediness of crops was observed by 16 and 8.5 pcs/m2 , respectively. When sowing soybeans according to zero technology, weediness was lower in the options with post-harvest sideral sowing of phacelia and buckwheat, where the number of weeds, compared to the control, was 10 and 16 pcs/m2 fewer. For all methods of the main tillage, an increase in soybean yield was recorded when using post-harvest green manures, which was 0.22–0.57 t/ha when sowing buckwheat on green manure, 0.06–0.23 t/ha when using white one-year-old sweet clover, and 0.29–0.67 t/ha when using phacelia. It was established that when growing soybeans in an irrigated short-rotation crop rotation in the Southern Steppe zone of Ukraine, the least weediness of crops and the highest crop yield at the level of 3.77 t/ha was provided by plowing to a depth of 28–30 cm. Sowing of post-harvest green manures contributed to an increase in soybean productivity from 0.06 to 0.67 t/ha. When growing soybeans according to zero technology, using buckwheat in the intermediate post-harvest sowings and phacelia for green manure can reduce weediness of the main crop by 24 and 39%, respectively, and increase productivity by 0.22 and 0.29 t/ha.