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.