Optimized tillage practices and row spacing to improve grain yield and matter transport efficiency in intensive spring maize

Subsoiling tillage practices and wide-narrow planting patterns could greatly improve grain yield through increasing post-silking dry matter accumulation of spring maize (Zea mays L.) under high plant density. However, the relationship between increased yield and vascular bundles structure, post-silking matter transport efficiency has not been unknown. Therefore, a field experiment was conducted on the Northeast plain of Liaoning Province in China in 2013 and 2014 to investigate the effects of four cultivation modes on post-silking matter transport under high plant density (105,000 plants ha−1). A widely grown maize hybrid Zhongdan 909, which exhibits high grain yield and tolerance to high plant density, has been used in our study. The four cultivation modes were (1) traditional rotary tillage (20 cm) plus uniform plant spacing (60 cm; RU; control); (2) subsoiling tillage (35-40 cm) plus uniform plant spacing (60 cm; SU); (3) traditional rotary tillage (20 cm) plus wide-narrow (80 + 40 cm) plant spacing (RW); and (4) subsoiling tillage plus wide-narrow plant spacing (SW). Compared to RU, wide-narrow planting (RW, SW) significantly optimized the canopy structure at silking, while SU and SW significantly optimized the soil structure, thus improved the photosynthetic rate and canopy radiation use efficiency (RUE), and post-silking dry matter accumulation (+5.2% [SU], +6.5% [RW], and +13% [SW]), and simultaneously reduced the C/N ratio in stems at maturity (−4% [SU], −27% [RW] and −39% [SW]), which led to the balancing of C and N in organs of maize at grain filling stage. Moreover, it also enhanced the differentiation of the vascular bundle system at the early growth stage, and maintained its function after silking by the better environmental conditions, which greatly improved the matter transport efficiency (+42%), and increased the grain filling rate. As a result, the yield for SU, RW, and SW increased by 5%, 7.5%, and 22%, respectively, compared to RU. These suggested that the optimization practices noticeably increased the canopy RUE after silking for spring maize by improving matter transport efficiency, stem vascular structure, and maintaining the balance between C and N metabolism, which eventually increased the grain yield under high plant density conditions. It might provide information of appropriate cultivation practices in enhancing grain yield for maize.