Influence of precursors and soil cultivation on oil and protein yield from soybean crops

Goal. To develop the basic parameters of bioadaptive soybean cultivation technology (Glycine max L.), determine their impact on the yield and quality of soybean seeds in the Steppe of Ukraine. Methods. Basic — field research, additional — laboratory and mathematical statistics (dispersion and correlation analyses). The research was carried out in the conditions of the Northern Steppe at the Institute of Agriculture of the Steppe of NAAS during 2010–2024 (soil-typical deep medium-humus heavy-carbonaceous chornozem). Results. For the use of plowing after winter wheat, corn for grain, and soybeans as precursors, the yield of soybeans increased to 2.22–2.26 tons/ha compared to the indicator for the predecessor of sunflower (2.10 tons/ha). The use of shallow tillage caused a significant shortage of soybean harvest in repeated crops of 0.09 t/ha, after corn for grain — 0.15, sunflower — 0.17, after winter wheat — 0.19 t/ha, compared to this value in plowing options. For direct sowing, the shortage of soybean harvest was 8.7–19.7%. The lowest soil hardness was during soybean cultivation in repeated crops for ploughing — 5.6–13.1 g/cm2, for shallow tillage — increased to 9.7–19.2 g/cm2, for direct sowing — to 11.6–23.6 g/cm2. After sunflower plowing, it increased to 6.6–14.8 g/cm2, with shallow tillage — to 11.1–21.6, without tillage — to 12.9–27.3 g/cm2, which negatively affected the growth and development of soybean plants. Due to the very strong inverse correlation between the oil content in soybean seeds and yield, even with a higher oil content in soybean seeds by direct sowing, the highest yield of oil from a unit of soybean crop area (0.46 t/ha) was achieved precisely for plowing after predecessors — soybean, corn for grain, and winter wheat. For direct soybean sowing after sunflower and corn for grain, the shortfall in oil yield was 0.05–0.06 t/ha, in repeated sowing — 0.03 t/ha. The highest protein yield (0.94–0.95 t/ha) was obtained for plowing after soybean predecessors — corn for grain and winter wheat, the lowest (0.68 t/ha) — for direct soybean sowing after sunflower. Conclusions. To form a stable productivity of soybean crops and a high yield of oil and protein in the conditions of the Northern Steppe of Ukraine, soybeans should be grown for plowing as the main cultivation of typical chornozem after the best predecessors — soy, corn for grain, and winter wheat. With direct sowing, soil hardness increases significantly, which leads to a reliable shortage of soybean yield (8.7–19.7%), a decrease in oil yield (by 6.5–17.4%), and protein (by 14.1–23.4%).