| More and more cotton cultivation land are transferring to the saline land because of the intensive competition of cotton growth and cereal growth in China, and the saline land (pH 7.8, total iron content 0.28%, electrical conductivity 4.52 ds m-1) in the northeast of Jiangsu are believed to the major cotton cultivation land of Jiangsu province in the further. Nowadays, the main problems need to be solved for cotton cultivation in saline land is low cotton yield, bad fiber quality and low nutrition efficiency. To overcome these problems in cotton cultivation, field experiments were carried out with different nitrogen application rates (0,150,300,375,450,600 kgN hm-2) at coastal saline land in Dafeng (33.2°N, 120.5°E), Jiangsu Province in 2010 and 2012 by using cotton cultivar Xiangza NO.8. The main results were as follows:1. The effect of nitrogen application rate on cotton yieldFor cotton yield development in the saline land of Dafeng, the fitful nitrogen application rate to obtain the highest yield is 375 kgN hm-2. The dynamic of the cotton plant dry matter accumulation followed a typical "S"curve, and in the 0-600 kgN hm-2 application rage, the biomass increased with the increasing of N application rate. For fiber yield development, the optimum nitrogen application rate is 375 kgN hm-2. Over nitrogen application will decrease cotton yield. The abscission decreased first and then increased with the increasing of nitrogen application rate, while the retention bolls increased first and then hold on a steady level in 300-600 kg hm-2 N application rate. The average boll weight increased rapidly with the increasing of N application rate in low N application level (0～300 kgN hm-2), and then hold on a steady level in 300～600 kg hm-2 N application rate. The highest lint percentage could be obtained in lower N application rate than the yield, and then it would decrease as the N increased.2. The effect of nitrogen application rate on fiber qualityFor fiber quality development in the saline land of Dafeng, N application influent the fiber quality development complicated, it’s hard to separate its advantage and disadvantage for a plant totally, but it is obviously that it could increase the quality of the fiber from the bolls set on the upper and top fruiting branches. The detailed influence was:higher N application (450～600 kgN hm-2) were beneficial to increase the fiber length for the bolls set on the upper and top fruiting branches, and the effect of over N application has no significant effect on the middle and lower fruiting branches. The change of N application rate had significant effect on fiber strength development, higher N application was beneficial to increase the fiber strength for the bolls set on the upper and top fruiting branches, while it adversely affect the fiber strength development for the bolls set in the middle and lower fruiting branches. The optimal N application rate for fiber strength development was around 300-375 kgN hm"2. Though the macronaire vale of fiber was not sensitive to the changes of N application rate in the middle branches, over N application have significantly increased it for the bolls set on the upper and top fruiting branches while have significantly deteriorated the macronaire vale of the middle fruiting branches. Over N could decrease the elongation rate of fiber from the lower branches while could enhance the elongation rate of the fiber from the upper and top branches. Data suggest that the uniformity of fiber were not changed significantly with the changes of N application rate. Thus, it can be concluded that 375 kg hm-2 N application can generally balance the aim of high yield, high quality and high N efficiency in the alleviated salty soil around the experimental station.3. The effect of nitrogen application rate on nitrogen utilizationIn the saline land of Dafeng, lint yield and NARE of cotton ascended firstly and then descended with the increasing of nitrogen application rate, and they reached their highest value at 301-374 kgN hm"2. NAE, NPP, NPE descended with the increase of nitrogen application rate. Nitrogen application rate changed the dynamic characteristics of nitrogen content and nitrogen accumulation amount of cotton plant, and subsequently affected the accumulation and translocation of biomass and nitrogen to reproductive organs, lastly resulting in affected yield of cotton. The eigenvalues of the dynamic model of nitrogen content and nitrogen accumulation in 301-374 kgN hm-2 nitrogen rates were more harmonious than that in other treatments. In excessive nitrogen supply rates, the nitrogen content and nitrogen accumulation rate in different fruiting branches were increased, the distribution index of biomass and nitrogen were descended and the duration of fleetly accumulation of nitrogen were elongated in low and middle fruiting branches, the proportion and amount of nitrogen uptake during boll maturing stage were increased, and lint yield were decreased. In deficient nitrogen supply conditions, the nitrogen content in different fruiting branches reduced, the reducing rate of nitrogen content were increased, the biomass and accumulation amount of nitrogen reduced, and subsequently the lint yield reduced.4. The effect of nitrogen application rate on phosphorus utilizationThe increased nitrogen application enhanced phosphorous uptake of cotton at different growth stages, with the highest increment from the peak flowering to boll opening stage, also, it changed the percentages of phosphorous uptake during different growth stages, thus, decreased the percentages of phosphorous uptake from the seedling to peak flowering stage but increased the percentages of phosphorous uptake from peak flowering to boll maturing stage. Nitrogen application helped lower the decreasing speed of phosphorous concentration of all fruiting branches, and the effect increased as the increasing of fruiting branches. The marginal effect of potassium uptake (Per unit of rise of phosphorous uptake due to 1kg increase in N application) showed an upward-downward trend with the increase of nitrogen application rate. The higher the fruiting branches laid, the more nitrogen amount demanded to meet the highest marginal effect of phosphorous uptake. By changing the dynamics of contents and accumulation of phosphorous in different fruiting branches, nitrogen application rate affected accumulation and translocation of biomass and phosphorous to reproductive organs, which then had lint yield influenced. As for lower fruiting branches, a relatively late time reached maximal rate of accumulation, and a relatively short duration of fleetly accumulation helped the transportations of photosynthates and phosphorous toward reproductive organ; As for middle fruiting branches, a relatively short duration of fleetly accumulation of phosphorous helped the transportations of photosynthates and phosphorous toward reproductive organ, yet as for the upper fruiting branches, a relatively high maximal speed of accumulation, a relatively late time reached maximal rate of accumulation, and a relatively short duration of fleetly accumulation of phosphorous, facilitated such transportations. A high yield was favored to meet with nitrogen at 300-375 kgN hm-2 levels, in which the economic coefficient of biomass and phosphorous were relatively high, eigenvalues of dynamic model of phosphorous concentration and accumulation stayed relatively coordinated, and the marginal effect of concentration uptake and lint production efficient of phosphorous were relatively high in middle and upper fruiting branches; Excessively high nitrogen application witnessed a relatively narrow rise of yield, and the marginal effect of phosphorous uptake and lint production efficient of phosphorous were relatively low. Excessively low nitrogen, however, adversely affect the high yield development, while economic and phosphorous harvest index would be low.5. The effect of nitrogen application rate on potassium utilizationIn the saline land of Dafeng, the increased nitrogen application enhanced potassium uptake of cotton at different growth stages, with the highest increment at the peak flowering to boll opening stage, also, it changed the percentages of potassium uptake during different growth stages, decreased the percentages of potassium uptake during the seedling to peak flowering stage but increased the percentages of potassium uptake from peak flowering to boll maturing stage. At later growth stages, increased nitrogen application was benefit to lower the decreasing speed of potassium concentration in middle and upper fruiting branches, but that had less influence on lower fruiting branches. The marginal effect of potassium uptake (Per unit of rise of potassium uptake due to 1kg increase in N application) showed an upward-downward trend with the increase of nitrogen application rate. The higher the fruiting branches lay, the more nitrogen amount demanded to meet the highest marginal effect of potassium uptake. By changing the dynamics of contents and accumulation of potassium in different fruiting branches, nitrogen application rate affected accumulation and translocation of biomass and potassium to reproductive organs, which then had lint yield influenced. As for lower and middle fruiting branches, a relatively short duration of fleetly accumulation of potassium helped the transportations of photosynthates and potassium toward reproductive organ, yet as of the upper fruiting branches, a relatively high maximal speed of accumulation of potassium, a relatively late presence of maximal speed of accumulation, and a relatively short duration of fleetly accumulation, facilitated such transportations. A high yield was favored to meet with nitrogen at 300-375 kgN hm-2 levels, in which the economic coefficient of biomass and potassium was relatively high, eigenvalues of dynamic model of potassium content and potassium accumulation stayed relatively coordinated, and the marginal effect of potassium uptake and lint production efficient of potassium were relatively high in middle and upper fruiting branches; Excessively high nitrogen application witnessed a relatively narrow rise of yield, and the marginal effect of potassium uptake and lint production efficient of potassium were relatively low; excessively low nitrogen, however, did bad for a high yield, as economic coefficient of biomass and potassium would be relatively low.6. Development and application of critical nitrogen dilution model and diagnose modelBased on the experimental data from the saline land of Dafeng, the critical N concentration dilution modeled was developed as Nc= 2.477max W-0.149. The same estimate of parameter a and b in critical dilution curve in the two year support the viewpoint that the critical N concentration dilution curve for cotton is independent of ecological region. Phosphorus and potassium concentration dilution under the critical N concentration was also built. Based on the critical N concentration dilution model, the model of allometric relationships 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) were developed. According to the allometric growth coefficient and NNI, the optimal N application rate in coastal saline land was determined, and the optimal N is 300-375 kgN hm-2. This is accordance with the optimal N rates determined by cotton yield. Since the model developed in this study is based on the actual growth rate of the cotton, it has the advantages of specific, exact, simple and biologically sound. The models can be used directly to estimate the intrinsic cotton nitrogen demand under coastal saline land. |
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