Submitted to: Agronomy Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 8/1/2003
Publication Date: 10/1/2003
Citation: Zhao, D., Reddy, K.R., Kakani, V.G., Koti, S., Read, J.J. 2003. Seasonal trends of cotton leaf nitrogen and pigment concentrations and hyperspectral reflectance [abstract]. Agronomy Abstracts. CD-ROM. Interpretive Summary:
Technical Abstract: Seasonal patterns of cotton leaf nitrogen (N) and the relationships between leaf hyperspectral reflectance and leaf N were determined in field-grown cotton in 2001 and 2002. In one study, fertilizer rates of 0, 56, 112, and 168 kg N ha-1 were applied in four replicates. In another study, four treatments of 0, 0.59, 1.17, and 2.34 L ha-1 of mepiquat chloride (PIX) were applied in four replicates. Spectral reflectance, chlorophyll and N concentrations of uppermost fully expanded mainstem leaves were measured periodically during the growing season. Leaf N concentration ranged from 16.4 to 52.3 g kg-1 dry weight across sampling dates, treatments, and individual plots. Leaf N concentration was highest around first floral bud (square) stage and declined linearly as plants aged. Compared with leaf N, chlorophyll concentration changed little during the growing season. Nitrogen fertilizer rate significantly affected cotton leaf N and chlorophyll concentrations. In both the N and PIX studies, linear relationships were obtained between leaf N and a simple ratio of leaf reflectance at wavelengths 517 and 413 nm (R517/R413) (R2 = 0.64 0.83, P<0.01). Leaf chlorophyll concentration could be estimated using either R708/R915 or R551/R915. The information may be used to monitor cotton N status and help producers make timely decisions of crop nutrient management.