Full-field straw mulching and fertilizer application improved the soybean seed yield through optimization of the root and canopy structure: A study case in Huang-Huai-Hai region

Increasing soybean seed production and obtaining more vegetable oil and vegetable protein are important measures to ensure global food security. The Huang-Huai-Hai region is the main production area of high-quality and high-protein soybeans in China. No-tillage with straw mulching seeding technology is a new soybean planting mode in this area, which can significantly improve seed yield. However, the yield increasing mechanism is still unclear. A split-plot experimental design was adopted, which includes the main plot of seeding practice and the subplot of fertilizer treatment. The soil bulk density, soil water content, soil temperature, soybean root morphology, leaf area index, photosynthetic characteristics, canopy light transmittance, dry matter accumulation, and their relationship with seed yield were investigated. With the increase of experimental years, soil bulk density in topsoil decreased gradually (down 8.63 %) under straw mulching seeding treatment. Straw mulching stabilized the surface soil temperature, especially avoiding excessive surface soil temperature (down 1.11 ℃), which was beneficial to soil moisture retention (up 11.53 %). Straw mulching seeding practice created a suitable soil environment and promoted root growth (i.e. root length, root surface area, and root volume), especially when combined with fertilizer application. Both straw mulching and fertilizer application improved the leaf area index (up 16.55 %) of soybean. Furthermore, the leaf area index of soybean under fertilization was significantly increased in the R3-R5 stage, while it was increased during the period of R5-R7 under straw mulching treatment. In addition, the highest net photosynthetic duration was found under straw mulching (107 d), followed by straw crushing (104 d), and straw removing (102 d). The average soybean yield under straw mulching treatment was 4589.9 kg ha⁻¹, which was increased by 15.2 % and 10.3 % compared to straw removing and straw crushing, respectively. Compared with no fertilizer treatment, the average soybean yield with fertilization was 4580.2 kg ha⁻¹, which was increased by 17.2 %. In conclusion, under semi-arid conditions, straw mulching seeding practice with fertilization application created a suitable soil environment beneficial in promoting the growth of soybean underground and above ground, ultimately improving the seed yield.