Effects of nitrogen application rates on main physiological characteristics of leaves, dry matter accumulation and yield of cotton cultivated in the Yellow River bottomlands

Soil in the Yellow River bottomlands is sandy and poor in fertility. To investigate the effects of nitrogen (N) application rates on main physiological characteristics of leaves, dry matter accumulation and yield of cotton cultivated in the Yellow River bottomlands, field experiments were conducted using transgenic Bt Cry1A+CpTI hybrid cotton 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 mm) in 0-20 cm soil layer are 12.3%, 28.0%, and 59.7%, respectively. The rates of the application of N fertilizer were 0, 150, 300, and 450 kg/hm2, respectively, and the ratio of the application of N fertilizer before the sowing, at the flowering stage and the peaking bolls setting stage was 0.4∶0.4∶0.2 .The experiments were carried out with a completely randomized design with three replications. The results show that leaf area index (LAI), the contents of chlorophyll and total N, the activities of GS and SOD in leaves of cotton are increased, and the content of MDA in leaves is decreased with the increased N fertilization which has a role in delaying senescence of leaves. The results also indicate that the N 300 kg/ha treatment is of advantage to the dry matter accumulation and distribution of reproductive organs of cotton relatively, the N 0 or 150 kg/ha treatments are of disadvantage to the dry matter accumulation, and the N 450 kg/ha treatment is of advantage to the vegetative growth and dry matter accumulation but disadvantage to the dry matter distribution of reproductive organs. The yield of seed cotton is the highest when N 300 kg/ha is applied which could increase the yield by 15.29%， 9.77% and 0.26% compared to the treatments of N 0, 150 and 450 kg/ha, respectively. Under the experimental condition of this study, we conclude that N 300 kg/ha should be applied when cotton is cultivated in Yellow River bottomlands.