ESTIMATING NITROGEN STATUS OF STRAWBERRY PLANTS FROM ITS SPECTRAL RESPONSE

Abstract

Application of nitrogen fertilizer to strawberry crop (Fragaria x ananassa Duch.) in Michoacan (Mexico) exceeds its requirements, increasing production costs and causing serious environmental problems. In order to adjust nitrogen fertilization to achieve maximum plant yield without exceeding nitrogen requirements, it is crucial that plant nitrogen status be closely and accurately monitored. Contrary to traditional nitrogen analysis methods, the estimation of plant nitrogen status from its spectral response is quick, non destructive and easy of automate. Several vegetation indixes were calculated from the leaf spectrum of plants cultivated in a hydroponic system with three level of nitrogen fertilization (0.1, 3 and 20 mM N), and four sampling dates. The Pearson correlation analysis was used to determine significant relationships among foliar nitrogen content, chlorophyll, biomass, and leaf area and density. Nitrogen fertilization at 3 and 20 mM nitrogen showed comparative stable growth, whereas plants biomass was decreased at 0.1 mM nitrogen. Among calculated vegetation indices, only green reflectance (R550), MTCI (MERIS Terrestrial Chlorophyll Index) and REP (Red Edge Position) were highly correlated to nitrogen content.