Effects of soybean growing practices on nitrogen-fixing nodule development and seed chemical composition

Abstract

The findings of a field study on the effects of soybean growing practices on nodule development and the biochemical composition of Glycine max L. seeds are discussed. The research was conducted under monsoon climatic conditions in the steppe zone of Primorye Region. The Far East region of Russia is a leading soybean-producing area in the country. Recently, G. max has attracted increasing attention not just as oil crop but as a vegetable crop. Due to the development of new varieties, advanced growing practices are required to ensure high-quality yield production. The research goal was to identify optimal growing practices for the vegetable-type soybean variety Namul that promoted maximum development of nitrogen-fixing nodules and the accumulation of protein and oil in seeds. The two-year study showed that nodule development was influenced not only by the growing practices but also by weather conditions. The highest nodule number at the first trifoliate leaf stage (8-28 nodules ha) was recorded in 2025. However, nodule number increased by the flowering stage 2.0-6.4 times depending on the experimental treatment in 2025, and 3.9-20.3 times in 2024. Depending on the year, nodule weight ranged from 0.04 to 0.28 g at the early growth stages and from 0.7 to 2.3 g at the flowering stage. Evidently, the conditions of 2024 were favorable for high protein accumulation in seeds (45.2-45.7%). The highest oil content in seeds was observed under wide-row sowing at a rate of 550 thousand seeds per ha in the third ten-days of May (22.6% in 2025). The research found a moderate positive correlation between seed protein content and both nodule number and total nodule weight (r = 0.62 and r = 0.51, respectively).