| Over-fertilization of N and irrational N fertilizer application strategy were prominent in cotton field in Yellow River Cotton Area of China. Field experiments and a pot experiment were carried out in this paper so as to investigate economic N rate, rational N fertilizer application strategy, to provide principles for N fertilizer management of cotton. The first field experiment was carried out at Anyang Henan in 2011-2014, and 6 N fertilizer treatments(0, 90, 180, 270, 360, 450 kg N/hm2) were set up using transgenic Bt cotton(Gossypium hirsutum L.) cultivars China Cotton Research Institute(CRI) 79,and there were three aspects of contents in the first field experiment: N rate effect on the yield of seed cotton, N use efficiency and physiological characteristics of functional leaf; effects of N fertilizer application strategy on soil Nmin in cotton fields; response of soil enzyme activity related to N utilization in cotton fields. The second field experiment was carried out in 2013-2014 with split block design, and there were 3 plant density treatments in main plot which were 30000, 52500, 75000 plant/hm2 respectively, and 4 N fertilizer dosage were set as split block treatments which were 0, 112.5, 225, 337.5 kg N/hm2 respectively, in order to study interaction of plant density and N level on yield of seed cotton, NUE of cotton. A pot experiment in 2013-2014 using isotope tracer technology was carried out to study effects of ratios of basal fertilizer and topdressing, topdressing period of N fertilizer on15 N yield of seed cotton and recovery. Two transgenic Bt cotton cultivars, CCRI 79 and CCRI 60 were adopted and 4 treatments were set up with N application ratios of the base fertilizer and topdressing at the initial flowering stage 1:1, 1:2 as well as total N topdressing at the initial flowering stage and the budding stage respectively, total N application rate of each treatment was the same with 3.5 g N/35 kg soil/pot. The main results were as follows:1. The average yield of seed cotton(3810.4 kg/hm2) of the three years was the highest when N 360 kg/hm2 was applied. According to the fertilizer effect equation between Yield of seed cotton and N application rate, the optimum doses of N was 299.7 kg/hm2,with optimizing yield of seed cotton 3845.5 kg/hm2. LAI, chlorophyll content of functional leaves at different growth period of cotton, net photosynthetic rate of functional leaves at initial flowering period increased with the increase of N application rate; with the increase of N application rate, GS activity and GOGAT activity of functional leaves at different growth period of cotton increased while GDH activity and NR activity of functional leaves at later growth stage of cotton declined with the increase of N application rate; MDA content of functional leaves at later growth stage of cotton declined with the increase of N application rate, and SOD activity declined accordingly. When N application rates were at 270, 360 kg/hm2, LAI(3.47-3.73) of cotton was appropriate and physiological activities of cotton functional leaves at boll opening period were much higher than those of other N treatments, which could guarantee material need for high yield of cotton. With N application rate increased, total N accumulation amount and yield of seed cotton were significantly increased quadratically, and a NUE and i NUE of cotton were remarkably declined with the increased N fertilization. PNUE of cotton with 180 kg/hm2 treatment was the highest among 6 treatments. NRE of cotton with 270 kg N/hm2 treatment was the highest among 6 treatments.2. Apparent N surplus value over the entire period of cotton in field experiment increased with the increase of total N application rate. Yield of seed cotton of N270(3/7) was improved than that of N270(5/5) and N270(7/3), but the difference was not significant. N uptake, a NUE and NRE of N270(3/7) were significantly higher than that of N270(5/5) and N270(7/3) respectively, and apparent N surplus value was significantly less than that of N270(5/5) and N270(7/3) respectively.3. Urease activity of soil in field experiment of cotton increased with the increase of urea application rate. Dehydrogenase and proteinase activity of soil in field experiment of cotton increased with the increase of urea application rate(0-360 kg N/hm2), while when urea application rate reached 450 kg N/hm2, dehydrogenase and proteinase activity of soil declined.4. In pot experiment, with the increase of fertilizer rate of the base N, percentages of N derived from fertilizer(Ndff) of different organs of cotton plants at the initial flowering stage increased significantly, and amplitude of the percentages of Ndff was 25.9-42.5. With the increase of fertilizer rate of the topdressing N, percentages of Ndff of cotton plants at the harvest stage increased significantly and amplitude of the percentage of Ndff of cotton plants was 26.9-54.1. Seed cotton yields of cotton plants with N(1/2) were highest among 4 treatments, and there was no significant difference between those of N(1/2) and N(1/1). 15 N uptake amounts, 15 N recovery rates of cotton plants with N(1/1) and N(1/2) at the harvest stage were significantly less than those with total N topdressing at squaring and initial flowering period respectively. 15 N recovery rates of cotton plants with N(1/1) at the harvest stage were less than those with N(1/2), and there was no significant difference between N(1/1) and N(1/2). 15N recovery rate of soil after the harvest with N(1/1) was higher than that with N(1/2), and there was no significant difference between N(1/1) and N(1/2).5. There were interactions between plant density and N rate on seed cotton yield and NUE. Seed cotton yield and NUE with medium density under medium N rate as well as high density under low N rate were much higher than other treatments. ANUE, N partial factor productivity(NPFP), i NUE, NRE and p NUE declined with increased N fertilizer rate. |
PDF Full Text Request