Abstract: Corn (Zea mays L.) plant density is known as a major factor determining the degree of competition between plants. Modern corn hybrids have several responses to light decline at large densities, such as keeping a erectophile plant type and elongating the maintenance of green leaves. Some researchers have pointed out that modern hybrids showed high levels in root vigor, ATPase activity, and soluble protein contents as well as the deep-vertical but narrow-horizontal distribution of roots in soils. However, the root competitive ability among cultivars that released in different years is little known. Denghai 3719 created a yield record of 21 t ha^-1 in 2005. To understand the root spatial distribution and competitive ability of Denghai 3719, an experiment was conducted in rectangle tanks for comparing the roots characteristics and the biomass of aboveground part between Denghai 3719 and Jinhai 5 (a hybrid widely cultivated in China as control). The cultivars were planted in two models, i.e., two plants per tank with the same cultivar and with each plant from both cultivars. Each model treated with two nitrogen levels (0 and 7.5 g N plant^-1). Under the nitrogen application condition, the two cultivars had a distinct biomass accumulation, but their root/shoot ratios were similar. Denghai 3719 took on superiority over Jinhai 5 both in the proportion and root vigor of shallow (0–20 cm) roots, as a result of an increase of nitrogen accumulation by 6% and biomass by 8% under competition, respectively. Under nitrogen deficiency, root/shoot ratio increased in both hybrids than that under nitrogen application, with Denghai 3719 and Jinhai 5 increased by 4% and 21%, respectively. Owing to the inferiority of Denghai 3719 over Jinhai 5 in respects of root/shoot ratio, and the proportion and root vigor of shallow (0–20 cm) roots under nitrogen deficiency, Denghai 3719 had a decrease in nitrogen accumulation by 8% and in biomass by 2% under competition, respectively. The results indicate that Denghai 3719 is more adapted to ni-trogen-efficient environment in view of root distribution and root vigor.

Key words: Summer corn, Root distribution, Root competition, Root/shoot ratio