Effects of seed orientation planting on root growth in summer maize

Seed orientation during planting significantly affects crop shoot growth; however, its effect on the root system remains unclear. To explore the effects of seed orientation on above- and below-ground growth, this study used cultivar of summer maize ( Zea mays L., Zhengdan 958) to conduct germination paper, soil pot, and field experiments, from 2020 to 2021. The experiments included two irrigation treatments (irrigation, and non-irrigation or drought) and four seed orientation plantings (tip pointed up, T-U; tip pointed down, T-D; embryo lying up, E-U; and embryo lying down, E-D). The root mass density, root length density, specific root length, soil water content, shoot biomass, and yield of maize were analyzed. The results showed that under irrigation treatment, the root systems of plants in the E-U group were the biggest (5% higher in deep root mass density and average root mass density, 48% higher in deep root length density, and 10% higher in average root length density); thus, the soil water consumption was increased by 18%, from bell-mouthed to grain-filling. Additionally, plants in the E-U group had a wider leaf growth azimuth (35%), larger leaf area index (7%), and higher shoot biomass (3%); therefore, the grain yield was also higher (8%). Our correlation analysis showed that grain yield was directly correlated with shoot biomass, ear number, and harvest index; and indirectly correlated with deep root mass density. Under drought conditions, the maize roots under normal T-D treatment had a faster growth rate (36%) and narrower root angle (43%), resulting in the highest root mass density in the deep soil layer (19%), as well as higher soil water consumption (5%); as a result, plants also had higher shoot biomass (6%), even with a narrower leaf growth azimuth. In conclusion, under adequate water conditions, the distribution of the aboveground parts and root system together contributed to the increased grain yield under E-U treatment. Under drought conditions, dry matter production under the normal T-D treatment was mainly affected by root distribution. In the future, adjusting seed orientation when planting may facilitate a further increase in shoot biomass accumulation and yield formation by coinciding with root and shoot development under drought stress.