Effects of kernel size and sowing depth on maize root growth in the middle Sichuan hilly area

Poorly executed mechanized seeding and frequent occurrence of seasonal drought in the hilly areas in middle Sichuan compresses the growth of maize. Using the main cultivar for this region, 'Zhenghong505', and adopting a split zone design with field and pot experiments, the effects of different kernel sizes and sowing depths on the growth and distribution of roots at the seeding and ear stages of maize were studied to provide a theoretical basis for mechanized precision sowing and drought-resistant cultivation of maize in this region. The results were as follows:1) Larger kernels and an appropriate shallow sowing depth (2-6 cm) can both significantly increase the germination rate. Compared with deep sowing (10 cm), the germination rate under shallow sowing (2 cm) increased by 6.5%. 2) The length, surface area, volume, and dry weight of roots arising from large kernels were significantly greater than those from small kernels. Although the differences in root growth gradually reduced with the growth process, the length, surface area, volume, and dry weight of the roots were still 28.6%, 25.0%, 22.4%, and 11.4% higher, respectively, than for small kernels at the silking stage. 3) At the 3-leaf stage, the root length, surface area, volume, and dry weight of roots arising from kernels planted at 2 cm and 6 cm were significantly higher than for those sowed at 10 cm depth, and these parameters for roots from kernels planted at 10 cm surpassed those for kernels planted at 2 cm by the 5-7-leaf stage. The length, surface area, volume, and dry weight of the roots arising from kernels planted at 10 cm at the silking stage were significantly higher (17.1%, 11.9%, 14.0%, and 10.4%, respectively) than those at the 2 cm sowing depth, and the roots in the 10-20 cm soil layer contributed to an increase in yield. 4) Kernel size had little effect on root distribution, but a sowing depth of 10 cm increased the root distribution rate in soil layers below 10 cm. 5) Yields from large and medium kernels were significantly higher (9.1% and 7.3%, respectively) than those from small kernels. Deep sowing effectively increased yields by 11.8% at 6 cm depth and 26.3% at 10 cm sowing depth compared with sowing at 2 cm. Large kernels were conducive to the establishment of well-developed roots, whereas sowing at an appropriate depth was conducive to the growth and downward distribution of roots in the middle and late stages, thereby increasing their water absorption capacity and drought resistance, ultimately achieving the increase in yield. Therefore, when planting maize, large and medium kernels should be selected and sown deeper appropriately.