Abstract
Spectral reflectance-based vegetation indices have sensitive characteristics to crop growth and health conditions. The performance of each vegetation index to a certain condition is different and needs to be interpreted, correspondingly. This study aimed to assess the most suitable vegetation index to identify the crop response against elevated air temperatures, heat stress, and herbicide damage. The spectral reflectance, yield components, and growth parameters such as plant height, leaf area index (LAI), and above-ground dry matter of paddy rice, which was cultivated in a temperature gradient field chamber to simulate global warming conditions, were observed from 2016 to 2018. The relationships between the vegetation indices and the crop parameters were assessed considering stress conditions. The normalized difference vegetation index (NDVI) represented the changes in plant height (R-square = 0.93) and the LAI (R-square = 0.901) before the heading stage. Furthermore, the NDVI and the cumulative growing degree days had a Sigmoid curve and an R-square value of 0.937 under the normal growth case, but it decreased significantly in the herbicide damage case. This characteristic was useful for detecting the damaged crop growth condition. Additionally, to estimate the grain yield of paddy rice, the medium resolution imaging spectrometer (MERIS) terrestrial chlorophyll index was better: R-square = 0.912; root mean square error = 95.69 g/m2. Photochemical reflectance index was sensitive to physiological stress caused by the heatwave, and it decreased in response to extremely high air temperatures. These results will contribute towards determining vegetation indices under stress conditions and how to effectively utilize them.
Highlights
Remote sensing is a useful technique to directly monitor crop conditions non-destructively [1,2]
The data for this study were obtained from the cultivation of paddy in a temperature gradient field chamber (TGFC) for three years; the purpose of this experiment was to study the crop response to various air temperatures in order to prepare for global warming
Grain yield can decrease due to external factors such as disease infection, heat stress, and lodging [51]
Summary
Remote sensing is a useful technique to directly monitor crop conditions non-destructively [1,2]. Crop spectral reflectance response varies depending on the distribution of crop biomass, crop conditions (e.g., disease, nutrition), and soil background [3,4,5,6,7] This response constitutes the vegetation indices developed to represent the structural, biochemical, and physiological characteristics of vegetation [8]. The data for this study were obtained from the cultivation of paddy in a temperature gradient field chamber (TGFC) for three years; the purpose of this experiment was to study the crop response to various air temperatures in order to prepare for global warming The growth parameters such as plant height, LAI, biomass, and grain yield were investigated, and spectral reflectance of paddy rice was measured using the spectrometer
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