在大田栽培条件下，于江苏南京（长江流域下游棉区）和河南安阳（黄河流域黄淮棉区）设置了棉花施氮水平试验，依据Justes的临界氮浓度稀释模型确定方法，研究棉花花后果枝叶临界氮浓度稀释模型及其与棉花产量的关系。结果表明, 花后棉花果枝叶的生物量增长和氮吸收累积均受施氮水平的影响，其动态变化符合S型曲线，氮累积的快速起始时间较干物质早2~4 d；棉花产量与果枝叶氮浓度关系密切，氮浓度过高或过低均不利于产量形成，花后果枝叶存在氮奢侈消费现象；棉花花后果枝叶氮浓度随施氮量的增加而增加、随生育进程而降低，其干物质累积量与氮浓度间符合幂函数关系，2试点果枝叶氮稀释曲线模型形式相同，但参数不同，不同气候区域存在独立的果枝叶氮临界、最高和最低稀释曲线模型；根据果枝叶氮浓度与产量间的关系，安阳、南京2试点，棉花果枝叶在盛花期和吐絮期的适宜氮浓度分别为4.93%、3.70%和3.33%、3.01%。临界氮稀释曲线的氮营养指数和异速生长模型对果枝叶氮营养状况的诊断与此相符。临界稀释模型具有明确的生物学意义，可以作为定量诊断果枝叶氮营养动态变化的指标之一。
Several field experiments with different levels of N application (0, 120, 240, 360, and 480 kg ha-1) were performed to investigate the responses of cotton growth and lint yield to a range of applied nitrogen treatments 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, and provide information better assessing the requirement of nitrogen and improving the fertilizer-nitrogen use efficiency for cotton. We established a model for cotton fruit-branch leaf and investigated its relationship with yield based on Justes, a critical nitrogen concentration dilution curve, which can be defined as the minimum nitrogen concentration required for maximum growth rate at any time. The results indicated that the biomass and nitrogen accumulation were greatly affected by nitrogen level for cotton fruit-branch leaf, and exhibited a sigmoid behavior when expressed as a function of time. The beginning time of fast accumulation period for nitrogen was 2–4 days earlier than that for biomass. The cotton lint yield was correlative with nitrogen concentration in fruit-branch leaf, which would cause the lint yield reduction when it was lower or higher than critical nitrogen value in fruit-branch leaf. Therefore the phenomenon of nitrogen luxurious consumption existed for fruit-branch leaf of cotton after flowering. The nitrogen concentration in fruit-branch leaf increased with the increasing of applied N rates, and decreased in the growing process. The relationship between the nitrogen concentration and dry matter of fruit-branch leaf can be described by a power equation. The patterns of nitrogen concentration dilution model were consistent at both experimental sites, but with different values for parameters. Therefore, the results presented in this paper backup the viewpoint that a critical nitrogen concentration dilution curve for cotton fruit-branch leaf is independent of ecological region. The maximum and minimum nitrogen concentration dilution curves can also be described with power equation, and are independent of ecological region. Relationships between total nitrogen accumulation and accumulated dry matter in fruit-branch leaf fit very well to the model Nupt=10 aW 1－b for each nitrogen fertilization level at two experimental sites. The cotton fruit-branch leaf in Anyang had a higher capacity of nitrogen accumulation than that in Nanjing for the same dry matter. The lower position of the critical nitrogen concentration dilution curve for the same fruit-branch leaf biomass in Nanjing indicated that the nitrogen biomass productivity was higher than that in Anyang. Because of having the biological sound for the critical N concentration dilution curve, it can be a reliable tool for diagnosing the nitrogen nutrition status of fruit-branch leaf. Therefore, the diagnosises made by the models of allometry and nitrogen nutrition index (NNI), which based on the critical nitrogen concentration dilution model, had a sound biological basis. According to the allometric coefficient, NNI and dynamic nitrogen accumulation rate under critical nitrogen concentration, the optimal rate applied nitrogen fertilization in Anyang which was 240–360 kg ha-1 and more does to 360 kg ha-1 should be higher than that in Nanjing which was 240 kg ha-1.
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