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The mulched drip technology has made rapid progress in Xinjiang, cotton fertilization key question is timely and appropriate application of nitrogen fertilizer SPAD (soil-crop analysis instrument developed abbreviation in the reproductive period, Soil and Plant Analyzer Development) non-destructive, fast diagnosis fertilization technology gradually been widely used, but the accuracy of the technology is also to be improved. This article typical cotton-growing areas in the arid region of Xinjiang Korla, a 2-year field experiment to study the cotton under drip irrigation fertilization total number of each growth stage dressing fertilization strategies on soil nitrogen, plant nitrogen and yield relationship with SPAD value, clear the number of samples to improve the accuracy of the SPAD value, to improve to improve cotton under drip irrigation nondestructive diagnostic techniques to improve the efficiency of nitrogen fertilizer use to provide a reference. The main conclusions are: (1) nitrogen fertilizer relatively abundant supply, high levels of cotton SPAD value from the bud stage to maintain the boll period into the boll opening stage before slow decline, SPAD value in the whole growth period to maintain a higher level, cotton overall can obtain high yield. Therefore, select the appropriate total amount of nitrogen fertilizer, effectively increasing effect of fine cotton growth period fertilization strategy. (2) Whether the level of fertilization, different nitrogen topdressing rate policy within the range of 0-60cm soil profile ,0-20cm, 20-40cm ,40-60cm layer of soil nitrogen content differences significant, soil available nitrogen with depth of the increase was the increase gradient: the same depth within the soil nitrogen content in the different nitrogen fertilization strategy is not the same: the required the recommended fertilization fertilizer Law proportion strategy in accordance with the cotton growth period fertilization, SPAD value and fertility of soil alkali solution nitrogen changes the highest correlation. Under different fertilization strategies, SPAD value reflects the cotton growing soil available nitrogen level of sensitivity vary. (3) whether it is a relatively low nitrogen rate high nitrogen application rate recommended nitrogen application, in accordance with the law of cotton nitrogen demand, the range of 20-40 cm of the soil profile nitrogen content and SPAD value change the most, followed by the soil profile the range of 40-60 cm, the correlation between the lowest range of 0-20cm of the soil profile. The selection of the soil profile within the range of 20-40cm soil alkaline hydrolysis nitrogen values, can improve the representative the SPAD values ??reflect soil nitrogen levels. (4) under the same nitrogen rate, different strategies to Nitrogen ratio of cotton nitrogen uptake and accumulation, the boll weight have a significant impact, and thus play a synchronous role in nitrogen uptake accumulation and cotton increased yields. Twice fertilization \the percentage of accumulation, coordination of the whole growth period nitrogen uptake by the accumulated amount of the highest level, is conducive to the high-yield formation. (5) the same amount of nitrogen under different nitrogen topdressing strategy of the shoot, leaves suck both the level of nitrogen and SPAD values ??varying degrees of impact, the blade suction level of N and SPAD in higher N and SPAD in the shoot suction level. Different nitrogen topdressing strategy, SPAD value of cotton and cotton plant aboveground nitrogen uptake, leaf suction nitrogen in the correlation between the level of performance of law. The SPAD value reflects the sensitivity of leaf nitrogen levels higher than the level of sensitivity of plants reflect Nitrogen. (6) cotton growth stages SPAD chlorophyll meter measurement, determination of the number of samples affect the mean accuracy of SPAD, the greater the number of samples SPAD higher mean accuracy, SPAD mean better correlation with leaf nitrogen content the SPAD value determination of the number of samples and the standard deviation into power function relationship.
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