Effect of plant density and nitrogen supply on nodel root number of maize of different varieties

【Objectives】 Brace and crown roots play dominant role in supporting plants and water and nutrient uptake during the whole growth period of maize. Plant density and nitrogen (N) supply are two important factors on maize growth and yield production, study their effects on the growth of brace and crown roots will provide base for the choose of proper cultivars.【Methods】 In this study, 10 maize hybrids, crossed from female inbred lines GEMS30, Zheng653, Mo17, B73, CIMBL153 and male lines Wu312 and Wu312 derivative lines, were grown in filed under two plant densities (60000 and 80040 plants per hm2). Three N supply levels of 0, 120 and 240 kg/hm2 were designed for the two densities. The variation of the number of brace and crown roots was counted by hand after the whole roots were dug out. The pulling resistance of the stalk was measured at the same time.【Results】 The grain yields were lower in high plant density than in low density, and lower in N 0 or N 240 kg/hm2 than in N 120 kg/hm2. N application rate, plant density and their interaction significantly affected the number of brace and crown roots. At high plant density, the number of brace roots was decreased by 3-6, the pulling resistance was decreased by 14%-29%, while the number of the crown roots was not affected. The highest number of brace roots and crown roots, as well as the strongest stalk pulling resistance were obtained under N 120 kg/hm2. There was genotypic difference in the number of brace roots in response to N supply and plant density. Two hybrids crossed from B73 as the female parent were mostly sensitive to N supply. Under 0 and N 120 kg/hm2, the number of brace roots was positively correlated to grain yield regardless the plant density. Under high plant density without N supply, the number of brace roots was negatively correlated to grain yield. Under low plant density without N or with N 120 kg/hm2, the number of crown roots was positively correlated to stalk pulling resistance. The most satisfactory number of the brace and crown roots, the stalk pulling resistance and the grain yield were obtained under low planting density and N 120 kg/hm2 supply. 【Conclusions】 In suitable production condition, more brace roots are good for high pulling resistance and high yield, but under stress condition, excess brace roots would inhibit the formation of maize yield. So the response of brace root number to stress should be considered for the choose of hybrids to obtain target yield.