Optimal Wheat Seeding Rate is Influenced by Cultivar‐Specific Topsoil and Subsoil Root Traits

Competition among plants for limited soil resources is influenced, in part, by seeding rate. This study aimed to investigate how cultivars that differ in root traits affect water acquisition and the optimal seeding rate. Three cultivars of winter wheat ( Triticum aestivum L.) with contrasting root systems (CW134, more roots in topsoil and less roots in subsoil; CH58, small root biomass; CH1, less roots in topsoil and more roots in subsoil) were sown at 180, 225, and 280 seeds m −2 in 2014–2015 and 2015–2016 in a semiarid farmland on the Loess Plateau of China. As the seeding rate increased, grain yield declined in CW134, with topsoil roots increasing and subsoil roots decreasing in both seasons. In contrast, both grain yield and subsoil roots increased in CH1, and the highest grain yield was produced by CH1 at 280 seeds m −2 in both seasons. Subsoil root traits had a positive effect on soil water consumption after anthesis, which was strongly affected by yield components in the dryer season (2015–2016). However, the reverse was true for topsoil root traits. In 2014–2015, the topsoil roots had a positive effect on soil water consumption before anthesis, and aboveground traits at anthesis had a greater positive effect on yield components. To maintain higher yields in semiarid environments, genotypes with more topsoil roots should have lower seeding rates to alleviate the negative effect of excessive topsoil roots on postanthesis water absorption, while the reverse may be true for genotypes with more roots in subsoil layers. Core Ideas Excessive topsoil roots negatively affected postanthesis water absorption under drought stress. Increased root length in subsoil layers helped exploitation of deep soil water after anthesis. In semiarid areas, genotypes with large topsoil root traits should use lower seeding rates. Increased seeding rates may help yields of genotypes with more roots in subsoil layers.