Effects of split nitrogen fertilization on physiological characteristics of leaves，dry matter accumulation and yield of cotton cultivated in the Yellow River bottomland

Soils in the Yellow River bottomland of Zhengzhou citys section are sandy and poor in fertility. To investigate the effects of nitrogen（N）split application ratios on main physiological characteristics of leaves，dry matter accumulation and yield of cotton cultivated in the Yellow River bottomland, we conducted a field experiment using transgenic Bt Cry1A+CpTI hybrid cotton cultivar, CCRI (China Cotton Research Institute) 72, in 2010. The contents of soil organic matter, total N, available N, available phosphorous and available potassium in 0-20 cm layer are 6.06 g/kg, 0.44 g/kg, 70.80 mg/kg, 9.27 mg/kg and 115.26 mg/kg, respectively. The contents of soil particles ( 0.002 mm, 0.002-0.02 mm and 0.02-2.00 mm) in 020 cm soil layer are 12.3%, 28.0%, and 59.7%, respectively. The N split application ratios before the sowing, at the flowering stage and peaking bolls setting stage were 0∶0.4∶0.6 (T1)，0.2∶0.4∶0.4 (T2)，0.4∶0.4∶0.2 (T3) and 0.6∶0.4∶0(T4), respectively. The amount of N fertilizer was 300 kg/ha of pure N. The experiment was carried out with a completely randomized design with three repetitions. The results show that the contents of N metabolism products (free amino acids, soluble protein and total N) in growing leaves of transgenic cotton tend to be increased with the advanced N fertilization, the N metabolism products tend to be increased firstly then decreased in functional leaves, and the contents of the N metabolism products are highest in leaves under the N split application ratio of 0.4∶0.4∶0.2 (T3). The contents of the N metabolism products tend to be decreased at the aging stage and shed stage. The content of chlorophyll and the activities of glutamine synthetase (GS), superoxide dismutase (SOD) in leaves appear the similar trends with the N metabolism products, while the content of malondialdehyde (MDA) is just the opposite. The N split application ratio of 0.4∶0.4∶0.2 (T3) is of advantage to the dry matter accumulation of cotton plant and to the distribution to reproductive organs in the middle and late cotton growing period, and an opposite tendency is displayed with the advanced or postponing N fertilization. Moreover, under the experimental condition of this study, the N split application ratio of 0.4∶0.4∶0.2 (T3) could increase seed cotton yield by 11.24%，4.15% and 5.47% compared to the ratios of 0∶0.4∶0.6 (T1), 0.2∶0.4∶0.4 (T2) and 0.6∶0.4∶0 (T4), respectively. We suggest that the N split application ratio of 0.4∶0.4∶02 should be used in transgenic cotton fields in the Yellow River bottomland.