Assessing Nitrogen and Potassium Deficiencies in Olive Orchards through Discriminant Analysis of Hyperspectral Data

By M. Gomez-Casero, Francisca López-Granados, José Manuel Peñá-Barragán, Montserrat Jurado-Expósito, L. Garcia-Torres, R. Fernández-Escobar. 2007

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ADDITIONAL INDEX WORDS. Leaf nutritional status, optimization of fertilization, visible and near-infrared wavelengths ABSTRACT. Hyperspectral reflectance curves of olive (Olea europaea L.) trees under different N or K treatments, and the best wavelengths or vegetation indices to discriminate between different N or K applications using discriminant analysis were investigated. Field hyperspectral studies were carried out in two olive orchards located at Cabra and Lucena (southern Spain) for N and K experiments, respectively, in 2004 and 2005. At Cabra, olive trees have been fertilized since 1993, and annual applications of N per tree consisted of 0 kg (N0), 0.5 kg (N1 (normal)), or 1 kg (N2 (high)). At Lucena, olive trees were fertilized since 1997, with 0%, 2.5%, and 5% K2CO3. Hyperspectral measurements were collected for each N and K treatments using a handheld field spectroradiometer (spectral range, 400-900 nm) in July of both years. To determine the nutritional status, a leaf analysis was carried out in July 2004 and 2005 at both locations. At Cabra, leaf N concentrations under N0 treatment were below the critical threshold, indicatingnutritionaldeficiencies.ReflectancecurvescorrespondingtoN1andN2showed higherreflectance valuesin the near-infrared (NIR) plateau than N0 treatments. Wavelengths within the NIR region (from 710-900 nm) were selected in both years for discriminating between N treatments, with an overall accuracy of up to 99.2%. At Lucena, when K was not applied, leaf K content was below the critical threshold, indicating that olive trees were under a nutritional deficiency. Wavelengths from 710 to 890 nm, and the normalized difference vegetation index {NDVI = ((R780 -R 670)/(R780 + R670)} were selected for discriminating K treatments with an overall accuracy of up to 94.4%. Classification matrices for cross-validation classified and misclassified cases into the nearest category. The results suggestthattheinductionofNorKnutritionaldeficiencyformorethan10yearsinolivetreesresultedindifferentleaf nutrient contents, and this consistently affected hyperspectral reflectance curves, mainly in the NIR region. These results are promising and could provide information for further work on the identification of N- or K-deficient olive trees using remote sensing.

Subfields: Analytical Chemistry, Ecology, Plant Science

View Paper: https://www.semanticscholar.org/paper/ff16862e36966179fc91148fdc49ac52bf865fa8