Effects of rotational pattern and fertilization application on soybean yield under straws returning of preceding crop

Field experiments were conducted from 2018 to 2020 at the Soybean Experimental Station of the Jiangsu Academy of Agricultural Sciences in Nanjing, Jiangsu Province. A split-plot design was used to study the effects of straw returning and fertilizer application on the nutrient utilization and yield of soybeans under different rotation patterns. The main plot factor was different rotation patterns with straw returning of preceding crop of soybean (wheat–soybean, garlic–soybean, leaf mustard–soybean, and winter fallow–soybean), while the sub-plot factor was fertilizer application (no fertilizer and nitrogen N, phosphorus P, and potassium K compound fertilizer 15∶15∶15 at 225 kg∙hm⁻²). The results showed that rotation pattern and fertilization application significantly affected the soybean yield and yield components under crop straw returning of preceding crop, and the two factors had significant interactive effects on the yield, yield components, plant morphological index, biomass, nitrogen accumulation and distribution, and disease rate of soybean, as well as soil total nitrogen, available nitrogen contents. Compared with the winter fallow–soybean planting pattern, the other three rotation patterns decreased soil bulk density and available nitrogen content but increased soil organic matter and total nitrogen contents. Plant height, stem diameter, height of the bottom pod, branch number per plant, total biomass, grain biomass, total nitrogen accumulation, and grain nitrogen accumulation were the highest under garlic–soybean and leaf mustard–soybean rotation patterns, which were beneficial for yield. The final yield increased by 4.40%–10.30% and 5.66%–7.09% under fertilization treatments and by 4.88%–8.23% and 2.19%–8.78% under no fertilization treatments compared to the winter fallow–soybean planting pattern, respectively. The wheat–soybean rotation pattern inhibited soybean plant growth, and the total biomass, grain biomass, total nitrogen accumulation, and grain nitrogen accumulation were the lowest. The harvest index of biomass and nitrogen and the nitrogen production efficiency were the highest, but the yield was the lowest in this case, decreasing by 2.80–7.30% in the fertilizer treatments and by 7.45%–11.18% in the no fertilizer treatment compared to the winter fallow–soybean planting pattern. Wheat straw returning increased the diseased plant rate, whereas the leaf mustard–soybean and garlic–soybean rotations decreased the rate of diseased plants. Compound fertilizer application promoted plant growth, reduced the rate of diseased plants, improved soil total nitrogen and available nitrogen contents, soybean biomass and nitrogen accumulation, and harvest density. Although harvest index and nitrogen use efficiency of soybean were low, the yield significantly increased. Compared with the no fertilizer application treatment, fertilizer application increased the soybean yields of the garlic–soybean, leaf mustard–soybean, and wheat–soybean rotations by 9.21%–13.01%, 7.97%–14.02%, and 15.00%–15.91%, respectively. Therefore, the garlic–soybean and leaf mustard–soybean rotation modes should be popularized. Under a wheat–soybean rotation pattern, high yield is achieved when wheat straw is returned to the field. In the wheat–soybean rotation, fertilizers must be applied after wheat straw is returned to the field to achieve high yield.