施氮量对棉花叶位SPAD值的影响及棉花氮素营养诊断

在不同施氮量和不同质地土壤条件下，研究了氮素水平对棉花叶片含氮量和叶绿素含量的影响。研究表明，棉花不同生育时期叶片含氮量不同，苗期、蕾期、花铃期、铃期叶片含氮量分别为28.1、27.4、32.2、30.9 g·kg^-1。在各时期不同处理的叶片含氮量，均表现出相同的规律，即随施氮水平的提高，棉花叶片含氮量增加。土壤质地不同（砂壤土、粘壤土）时，高、中、低产棉田棉花叶片含氮量存在差异；随着施氮量的提高，棉花叶片含氮量随之提高，同时棉花不同叶位间的含氮量更加接近。对叶绿素的分析表明，不同施氮水平下，叶绿素含量差异显著；相同施氮水平下，不同叶位叶片SPAD值差异显著；施氮量增加能够提高棉花叶片的SPAD值，同时减小棉花不同叶位间SPAD差值的大小。初花期和花铃期顶1叶的叶位差指数PDI与棉花叶片含氮量的相关性最高，可以用叶位差指数作为衡量棉花氮素状况的指标。

Effects of nitrogen fertilizer rate on SPAD of cotton leaves and diagnosis of nitrogen nutrition

Chlorophyll and nitrogen content of each leaf on main stem of cotton plant under different nitrogen application rates and soil properties were investigated. The results showed that nitrogen content of leaves varied with growth stages, being 2.83%, 2.74%, 3.22%, and 3.12% for seedling, bud, flowering, and boll stage, respectively. Leaf nitrogen content increased as nitrogen rate increased for all the treatments. There were significant differences in leaf nitrogen content between the soils of sandy loam and clay loam. The analysis showed that the differences in chlorophyll content were significantly under different nitrogen levels, and it also varied with leaf position. Nitrogen fert ilizer increased cotton leaf SPAD values, while there was no marked difference in SAPD value between leaf positions. In addition, leaf color was significantly different between the 4th and the 1st leaf from the top, which was correlated with the plant nitrogen content at flowering stage and flowering-boll stage. Therefore, color difference between the 4th and the 1st leaf from the top could be used for diagnosis of plant nutrition status.