Inflection point position as a potential diagnostic tool for the estimation of sulfur concentration in Eucalyptus seedlings

Abstract

Specific techniques of spectral analysis to determine the nutritional stress caused by sulfur (S) may allow the early detection of its deficiency and directed supplementation in the corrective fertilization of plants. The aim of this study was to verify the alterations caused by S deficiency as well as to verify whether the spectral reflectance, that is, the inflection point position (IPP), obtained from a mini-spectrometer, can estimate S concentration and detect its deficiency in Eucalyptus urophylla seedlings. Seedlings were cultivated for 90 d in complete nutrient solution (without S omission) and with S omission. Sodium sulfate was used as a source of S. Sulfur deficiency caused changes in the morphological and physiological properties of the plants, which were reflected as changes in their leaf spectral properties. Visual symptoms of S deficiency, such as chloros is in new leaves and reductions in seedling growth started at 28 d after treatment application (DAT), reduction in height, diameter, and dry matter production were observed at 75 DAT. Nutritional analysis detected a reduction in leaf S concentrations and its deficiency in plants only at 45 DAT. However, at 30 DAT S deficiency changed seedling reflectance with S omission, shifting IPP to shorter wavelengths (± 700 ηm); that is, mini-spectrometer was able to detect the S deficiency in Eucalyptus plants. The IPP close to 700 ηm is a very sensitive indicator of S content and deficiency, demonstrating its great potential as a diagnostic tool to estimate leaf S content in Eucalyptus plants using a mini-spectrometer.

Keywords:

• Eucalyptus
• macronutrients
• mini-spectrometer
• nutritional deficiency
• spectral reflectance
• vegetation indices

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.