Weak border effects and great uniformity increase yield of maize (Zea mays) under dense population

The effects of uniformity in border rows and population structure on the yield of hybrid maize (Zea mays L.) grown at high planting density was studied in field experiments at Qitai Farm (89°34′E, 44°12′N), Xinjiang, China, during 2013 and 2014. The experiments incorporated a planting density of 12.0 plants m–2 and three maize cultivars (M753, LY66, LD565). Border effects and uniformity in the border rows were studied at the silking and maturity stages. Yields of M753, LY66 and LD565 were 16.46, 15.02 and 11.45 Mg ha–1, respectively. Analysis of yield components in border rows indicated that the number of kernels per ear, 1000-kernel weight and yield per plant of M753 stopped decreasing after the second row in the border, whereas those of LY66 and LD565 stopped decreasing after the third row in the border, demonstrating a stronger border effect. The cultivars intercepted >95% of the light, but light transmission was lower for M753 than for LY66 and LD565, which resulted in the highest light interception in the upper canopy layers of M753. Analysis of uniformity in the border rows showed that the uniformity values for plant height, ear height, stem diameter, number of kernels per ear, 1000-kernel weight and yield per plant were higher for M753 than for LY66 and LD565. For the three cultivars, uniformity values could be ranked in the order plant height > ear height > stem diameter. The results suggest that cultivars with weaker border effects and greater uniformity in border rows can produce higher yields when grown at a high planting density.