Subsoiling before winter wheat alleviates the kernel position effect of densely grown summer maize by delaying post-silking root-shoot senescence

Intensified kernel position effect is a common phenomenon in maize production under higher plant density, which limits the crop productivity. Subsoiling is considered as an effective agronomic practice to improve crop productivity. In order to clarify the effect of subsoiling before winter wheat on kernel position effect of densely grown summer maize and its regulatory mechanism, field experiments were conducted during 2020-2021 and 2021-2022 growing seasons by using a split-plot design. Main plot include two tillage practices: conventional tillage practice (CT) and subsoiling before winter wheat (SS); subplot consist three plant densities (D1-D3, 6.0×104, 7.5×104, and D3, 9.0×104 plants ha-1). Compared with CT, SS alleviated the kernel position effect by increasing the weight ratio of inferior to superior kernel (WR) of D2 and D3 treated plants. The higher WR of SS treated plants attribute largely to the improved filling of inferior kernel. Under the same plant density, SS significantly improved the root dry matter accumulation (DMA) and antioxidant enzyme activities (SOD and POD), and reduced malondialdehyde (MDA) concentration, especially for the plants grown under higher plant densities. These result indicated that SS delayed the root senescence, which is associated with the reduced soil bulk density. In addition, by comparison with CT, SS increased the leaf chlorophyll content from 20 days after silking to physiological maturity and post-silking leaf area duration, and decreased post-silking leaf chlorophyll reduction rate and leaf area reduction rate, reflecting the post-silking leaf senescence is alleviated. Under the same plant density, the post-silking DMA of SS was obviously higher than that of CT, which is probably related to the improved leaf area duration and photosynthetic enzyme activity (PEPC and Rubisco). The correlation analysis revealed that the main mechanism of SS in alleviating kernel position effect of densely grown summer maize is: SS delayed the post-silking root-shoot senescence by regulating soil physical properties, and further improved the post-silking DMA and filling of inferior kernel, ultimately alleviated the kernel position effect and improved grain yield. The present result will provide a new theoretical support for the promotion of summer maize yield by subsoiling before winter wheat.