Effects of nitrogen application rate on the nitrogen uptake and utilization of cotton grown in coastal saline fields of Yangtze River Valley

【Objectives】 Unreasonable nitrogen application has been a main problem in cotton cultivation in the coastal saline land of Yangtze River Valley. The aim for this study was to identify the response of nitrogen uptake and utilization of cotton grown in the coastal saline land of Yangtze River Valley to nitrogen application rate, and provide theoretical support for reasonable nitrogen application in the area. 【Methods】 Field experiments were carried out with different nitrogen application rates(0, 150, 300, 375, 450 and 600 kg/hm2) in coastal saline land in Dafeng(33.2°N,120.5°E), Jiangsu Province in 2010 and 2012. A cotton cultivar, Xiangza No.8, was selected for the study. The cotton yield, biomass accumulation and distribution, nitrogen uptake and utilization were investigated. 【Results】 The lint yield and nitrogen apparent recovery efficiency(NARE) of cotton are increased firstly and then descended with the increase of nitrogen application rate, and reach their high values under 301-374 kg/hm2. The nitrogen agronomic efficiency(NAE), nitrogen partial factor productivity(NPP), and nitrogen production efficiency(NPE) are descended with the increase of nitrogen application rate. The dynamic characteristics of the nitrogen content and nitrogen accumulation amount of cotton plant are changed under the nitrogen application, and affect the accumulation and translocation of biomass and nitrogen to reproductive organs and lastly affect the yield of cotton. The eigenvalues of the dynamic model of the nitrogen content and nitrogen accumulation in 301-374 kg/hm2 nitrogen rates are more harmonious those of the other treatments. In excessive nitrogen supply rates, the nitrogen content and nitrogen accumulation rate in the all fruiting branch parts are increased, the duration of fleetly accumulation of nitrogen is elongated and the reproductive distribution of biomass and nitrogen are descended in low and middle fruiting branch parts, the proportion and amount of nitrogen uptake at the boll maturing stage are increased, and the lint yield is decreased. In deficient nitrogen supply conditions, the nitrogen content in the all fruiting branch parts is reduced, the reduced rate of nitrogen content is increased, the biomass and accumulation amount of nitrogen are reduced, and subsequently the lint yield is reduced. 【Conclusions】 According to the results of the two-year field experiments in the coastal saline land of Yangtze River Valley, N of 301-374 kg/hm2 is considered as an appropriate nitrogen application rate for cotton production in the area. Excessive nitrogen supply will cause yield loss because of the reduces of the reproductive distributions of biomass and nitrogen in low and middle fruiting branch parts, and increase the proportion and amount of nitrogen uptake at the boll maturing stage. Deficient nitrogen supply reduces the lint yield due to the decrease of the nitrogen content in the all fruiting branch parts, and reduces the biomass and accumulation amount of nitrogen.