Development And Application Of Critical Nitrogen Concentration Dilution Model For Cotton

Nitrogen (N) is one of the primary nutrition to the production and fiber quality of cotton. According to dynamic characteristics of accumulation of biomass and N, the N requirement in different growth stages can be calculated. Therefore the theoretical basis of accurate fertilization could be offered for cotton production. By using the US cotton 33B as experimental material, field experiments with different levels of N application (0, 120, 240, 360, and 480 kg·ha^-1) were carried out in Nanjing and Anyang, standing for the ecological conditions in the middle lower reaches of Yangtze River Valley and Yellow River Valley in China, respectively, in 2004. Based on the study about dynamic characteristics of biomass and N accumulation and N fertilization recovery rate of cotton plant after flowering, the critical N concentration dilution curve model for cotton was developed. The dynamic models of critical N demand and quantitative diagnosis on dynamic N demand on which based the models of critical N concentration dilution curve and sigmoid curve of biomass accumulation. The main results were as follows:The accumulation of biomass and N for plant (including roots), aboveground, fruiting branch leaves, and reproductive organ of cotton continuously increased with the progress of plant growth after flowering, the general pattern of crop growth followed a sigmoid function of time. The levels of N did not affect the pattern of model, but affected the coefficients significantly. The eigenvalues of the dynamic accumulation model with the N application level of 360 kg·ha^-1 and 240 kg·ha^-1 for Anyang and Nanjing, respectively, were more harmonious than that with other treatments. The maximum accumulation rate and initial day of faster accumulation period appeared earlier than did the biomass in all treatments, and the accumulation rates per day and lint yields were also higher than that with other treatment. Due to more N accumulated in the nutrient organic and less nutrition and dry matter transferred from nutrient organic to reproductive organ, the economical yield become lower, though higher biomass can be obtained. Excessive N delayed cotton maturity and increased the proportion of vegetative organs, thereby reduced there quality and lint yield.The fact that the initial day of faster N accumulation period earlier than did the dry matter (4-7 d for total plant, 2-4 d for fi'uit-branch leaf, and 1-4 d for reproductive organ) indicated that N uptake was the base for dry matter accumulation.The dynamic developments of N fertilization recovery rate behaved in a very similar way as the cotton biomass did at two experimental sites. The N recovery rate and momentary N recovery rate reached their highest value at the N application level of 360 kg·ha^-1 and 240 kg·ha^-1 for Anyang and Nanjing, respectively. The N recovery rate in Nanjing was significantly higher than that in Anyang, which indicated that N accumulation of cotton was influenced by various endogenous and exogenous factors (such as N rate supplied, soil, and climatic factors).N is one of the key elements in achieving consistent and sustainable high yields and superior quality in cotton. The weight per boll and boll number per plant were the most important contributors to lint yield. The lint yield increased with the increasing N rate supplied, and registered its highest value at 360 kg·ha^-1 and 240 kg·ha^-1 for Anyang and Nanjing, respectively. Fiber strength, length, and elongation also reached their highest values at the optimal rates of application N and decreased at higher rates. Fibre micronaire tended to decline with the increasing of N rate. There was no statistical difference in fibre uniformity among N treatments and between two sites. With the optimal N rates applied the fibre length, strength, micronaire, elongation and uniformity for Anyang and Nanjing were 29.7mm,30.6mm, 28.5 CN/tex, 32.2 CN/tex, 7.7%, 6.9%, 3.8, 5.3, and 83.6%, 84.7%, respectively.The N concentration in aboveground biomass of cotton was diluted with the process of biomass accumulation. The results presented in this paper validate the concept of Greenwood et aI. (1990) that N concentration in plant aerial biomass decreases with increasing plant biomass, and that a dilution curve for critical N concentration (No%) can be described by a power equation:N_c=aW_max^-b (1)Where N_c stands for the critical N concentration, W_max the aboveground biomass expressed in Mg ha^-1 when the N concentration equal to N_c, a represents the N concentration in aboveground biomass when W=I Mg ha^-1, and b is a statistical parameter governing the slope of the relationship curve.According to the method proposed by Justes et al. (1994), the critical N concentration model was as follows:Anyang: N_c = 3.387W_max^-0.131 (2)Nanjing: N_c = 2.858W_max^-0.131 (3)The fact that the values were similar for parameter b in two models indicated that environment conditions did not really affect the slop of the critical N concentration dilution curve. The difference between two values of coefficient a in two sites showed that there was a independent critical N concentration dilution curve model in different ecological region.The N concentration dilution also existed in fruiting branch leaves, and reproductive organ of cotton. The independent critical dilution models were obtained respectively in Anyang and Nanjing.Based on the models of critical N dilution curve and sigmoid curve of dry matter accumulation, a series of models were developed as follows: (1) instantaneous N uptake rate model; (2) instantaneous critical N uptake rate model; (3) instantaneous N uptake deficit rate model; (4) accumulation of N uptake model; (5) critical accumulation of N demand model; (6) deficit accumulation of N model.According to these models, the maximum critical N uptake rate were 5.3 kg·ha^-1·d^-1 and 4.4 kg·ha^-1·d^-1 respectively in Anyang and Nanjing, and appeared consistently at 42 d after flowering. The growth stages after flowering from 23 to 59 d and from 23 to 61 d were the faster periods of N accumulation. The critical N demand per day in Anyang was higher than that in Nanjing. 26% and 27% of total N application rate should be applied at the time of soil preparation for Anyang and Nanjing, and the supplemental N should be applied at 22 d after flowering.Based on the critical N concentration dilution curve model, the model of allometric relationships (N_uptc=10aW_max^1-b: the coefficient 10a represents the amount of N present in the shoots when aerial dry matter weight is 1 Mg·ha^-1 and 1-b is the allometric ratio between N accumulation and dry matter accumulation in shoots.) between crop N uptake at each N application level and accumulated dry matter in the shoot biomass, and the model of N nutrition index (NNI=N_it/ N_ic: where N_it stands for the N concentration measured in the plant aboveground dry matter, and N_ic the critical N concentration for the same plant aerial biomass.) were developed.According to the allometric growth coefficient, NNI and N accumulation rate under critical N concentration, the following conclusion can be extracted: (1) Despite the difference of biomass and lint yield between Anyang and Nanjing, the eigenvalues of the dynamic biomass accumulation model were consistent. (2) The optimal rote of N application in Anyang should be higher than that in Nanjing, and the optimal N application rate is 360 kg ha^-1 and 240 kg ha^-1 in Anyang and Nanjing, respectively.