Abstract: We examined the effects of plant growth regulator ‘Yuhuangjin’ (30% amine fresh ester·ethyl hydroxide) and three nitrogen application rates (100, 200 and 300 kg·hm^-2 , designated as N100, N200 and N300, respectively) on dry matter accumulation, stem mechanical characteristics and yield of spring maize (variety ‘Longyu 365’) under high planting density (90000 plants·hm^-2). The results showed that chemical control increased grain number per ear and 1000-grain weight, and reduced the length of  ear bald tip and leaf area at each growth stage. Meanwhile, chemical control increased the amount of dry matter per plant and contribution proportion of the dry matter after anthesis by 7.9% and 3.2% respectively, compared with the control. The chemical control increased breaking resistance, stalk rind penetration strength and minimum diameter of basal internode as well as significantly reduced the internode length, and thus increased lodging resistance and increased yield by 8.7%. The yield, grain number per ear and leaf area of maize attained the maximum value under N200 treatment and the length of  ear bald tip was reduced. The amount of dry matter per plant and contribution proportion of the dry matter after anthesis under N200 treatment increased by 24.5% and 9% respectively, compared with those of N100 and N300 treatments. With increasing nitrogen application rate, breaking resistance and stalk rind penetration strength of basal internode reduced significantly, the maximum and minimum diameters first increased and then decreased, and the basal internode length significantly increased. The maize yield was significantly positively correlated with contribution proportion of the dry matter after anthesis (r=0.489^*) and leaf area of milking (r=0.819^*), and the maximum diameter (r=0.517^*) and the basal internode length (r=0.505^*) were significantly positively correlated with the dry matter after anthesis. The stalk breaking resistance was significantly negatively correlated with the basal internode length (r=-0.84^**) and was significantly positively correlated with the maximum diameter of basal internode (r=0.495^*). The stalk rind penetration strength of basal internode was significantly negatively correlated with basal internode length (r=-0.724^**).  Our results indicated that the combination of 200 kg·hm^-2 nitrogen application rate and chemical control provided the best lodging resistance and obtained the highest yield for spring maize under 90000 plants·hm^-2 in Heilongjiang Province.  Our results provided basis for the technology of chemical control to prevent lodging, reduce nitrogen application rate and increase yield under high planting density of spring maize in Heilongjiang Province.

Key words: Apis cerana cerana Fab., Honeybee queen, Drone, Copulation, Oviposition