Effects of mechanical direct seeding synchronous deep fertilization on winter rapeseed stem lodging resistance and yield

Rapeseed has been one of the most important cash crops to ensure edible oil safety in China. A mechanical direct seeding can be widely used in rapeseed production for labor-saving, high yield, and efficiency, particularly for the large-scale transfer of rural labor force under rapid economic transformation in recent years. However, there is usually a smaller root-shoot ratio of mechanized direct-seeded rapeseed, leading to the rape lodging and yield reduction. Alternatively, deep fertilizer is widely applied to determine the lodging resistance and yield in fertilization management and crop production, due to the high yield, fertilizer saving, and efficiency. Nevertheless, deep fertilizer can also increase the plant height, the height of the center of gravity, and dry matter mass, further inducing the risk of stem lodging. Furthermore, there are only a few studies on the lodging performance of crops under deep fertilizer, especially for the mechanized direct-seeded rapeseed. This study aims to investigate the effect of mechanical direct seeding synchronous deep fertilization on the stem lodging resistance and yield of winter rapeseed. A field experiment was carried out at Jianli and Shayang County in Hubei Province of China from October 2020 to May 2021. Rapeseed (variety: Huayouza 62) was selected as the experimental material. Three treatments were designed, including deep, mixed, and no fertilizer (control). A systematic evaluation was made on the root, stem development, dry matter accumulation, nitrogen uptake, lodging resistance, and yield of winter rapeseed. A response of lodging resistance and yield to the plant type was then determined under mechanical direct seeding with different fertilization treatments. The results showed that the deep fertilizer significantly promoted the growth and development of the rapeseed, and simultaneously accompanied the high lodging indices of the stem. The stem diameter, dry weight of stem, shoot fresh weight of winter rapeseed, and breaking resistance of stem increased (P<0.05) by 9.5%, 16.6%, 17.4%, and 31.5%, respectively, under deep fertilizer, compared with the mixed fertilizer. Moreover, both the plant height and shoot fresh weight increased less than the stem breaking resistance under deep fertilizer, indicating a 5.0% reduction of lodging index. There was also a 23.2%, 20.4%, and 27.4% increase in the dry weight of root, the dry weight of aboveground biomass, and nitrogen accumulation in the aboveground rapeseed with the deep fertilizer, respectively, indicating a significant increase in the crop yield by 20.7% (P=0.014) and harvest index by 2.0%. Consequently, the deep fertilizer can be expected to enhance the stem lodging resistance of winter rapeseed for a better population structure, while, mechanized planting can be used to achieve a high yield and low lodging risk of rapeseed. In addition, a future exploration still remains on the suitable fertilization depth for the higher yield and lower lodging of mechanized direct-seeded rapeseed, and the physiological mechanism of lodging resistance under deep fertilization.