Reflectance spectrometry applied to the analysis of nitrogen and potassium deficiency in cotton

ABSTRACT The detailed study of hyperspectral data that optimise the management of agricultural inputs can be a powerful ally in the nutrient diagnosis of plants. This study characterised variations in the reflectance factors of cotton leaves (Gossypium hirsutum L.) of the BRS 293 cultivar, submitted to different levels of N and K fertilisation. A total of 166 plants were submitted to four doses of N and K, with twenty replications and six controls. Each treatment represents one level of fertilisation: 50, 75, 100 and 125% of the recommended amount of both macronutrients at each stage of the phenological cycle. The spectroradiometer used in the laboratory was the FieldSpec Pro FR 3® with a spectral resolution of 1 nm and an operating range that extends from 350 to 2500 nm. In both treatments, PCA allowed wavelengths to be idenbtified grouped by such parameters as brightness, chlorophyll and leaf moisture. The N and K fertilisation caused significant changes in the factors, where the greatest difference between doses was seen at 790 and 1198 nm. The wavelengths between 550 and 700 nm and at 1390 and 1880 nm were, respectively, the most promising for explaining the variance in nutrient levels of N and K in cotton.

摘要 针对可优化农业投入品管理的高光谱数据开展的精细化研究，可成为植物养分诊断的有力辅助手段。本研究针对施加不同水平氮（N）、钾（K）肥料的BRS 293品种陆地棉（Gossypium hirsutum L.）叶片的反射率因子变化进行了表征分析。本实验共纳入166株供试植株，设置4种氮、钾肥施用量梯度，每组处理设置20次重复，另设6组对照组。每组处理对应一种施肥水平：即物候期各阶段中，两种大量元素的施用量均为推荐用量的50%、75%、100%与125%。实验室采用的光谱辐射仪为FieldSpec Pro FR 3®，其光谱分辨率为1 nm，工作波段范围覆盖350~2500 nm。在所有处理组中，主成分分析（PCA）可识别出与亮度、叶绿素及叶片水分等参数相关的波段分组。施加氮、钾肥会显著改变叶片反射率因子，不同施用量梯度间的最大差异出现在790 nm与1198 nm波段处。550~700 nm波段与1390~1880 nm波段，分别是解释棉花氮、钾养分含量变异最具潜力的波段区间。