Time-Series of Vegetation Indices (VNIR/SWIR) Derived from Sentinel-2 (A/B) to Assess Turgor Pressure in Kiwifruit

Abstract

Simple Summary: Measures of plant water status on kiwifruit were evaluated using Sentinel-2 (A/B) for two seasons in Central Chile. For more than ten years, Central Chile has faced drought conditions, which impact crop production and quality, increasing food security risk. Under this scenario, implementing management practices that allow increasing water use efficiency is urgent. The study was carried out on kiwifruit trees, located in the O'Higgins region, Chile for season 2018-2019 and 2019-2020. We evaluate the time-series of nine vegetation indices in the VNIR and SWIR regions derived from Sentinel-2 (A/B) satellites to establish how much variability in the canopy water status there was. Over the study's site, eleven sensors were installed in five trees, which continuously measured the leaf's turgor pressure (Yara Water-Sensor). A strong Spearman's (rho) correlation between turgor pressure and vegetation indices was obtained, having -0.88 with EVI and -0.81 with GVMI for season 2018-2019, and lower correlation for season 2019-2020, reaching -0.65 with Rededge1 and -0.66 with EVI. However, the NIR range's indices were influenced by the vegetative development of the crop rather than its water status. The red-edge showed better performance as the vegetative growth did not affect it. It is necessary to expand the study to consider higher variability in kiwifruit's water conditions and incorporate the sensitivity of different wavelengths.

Simple Summary: Measures of plant water status on kiwifruit were evaluated using Sentinel-2 (A/B) for two seasons in Central Chile. For more than ten years, Central Chile has faced drought conditions, which impact crop production and quality, increasing food security risk. Under this scenario, implementing management practices that allow increasing water use efficiency is urgent. The study was carried out on kiwifruit trees, located in the O'Higgins region, Chile for season 2018-2019 and 2019-2020. We evaluate the time-series of nine vegetation indices in the VNIR and SWIR regions derived from Sentinel-2 (A/B) satellites to establish how much variability in the canopy water status there was. Over the study's site, eleven sensors were installed in five trees, which continuously measured the leaf's turgor pressure (Yara Water-Sensor). A strong Spearman's (rho) correlation between turgor pressure and vegetation indices was obtained, having -0.88 with EVI and -0.81 with GVMI for season 2018-2019, and lower correlation for season 2019-2020, reaching -0.65 with Rededge1 and -0.66 with EVI. However, the NIR range's indices were influenced by the vegetative development of the crop rather than its water status. The red-edge showed better performance as the vegetative growth did not affect it. It is necessary to expand the study to consider higher variability in kiwifruit's water conditions and incorporate the sensitivity of different wavelengths.