Abstract
Drought significantly limits wheat productivity across the temporal and spatial domains. Unmanned Aerial Systems (UAS) has become an indispensable tool to collect refined spatial and high temporal resolution imagery data. A 2-year field study was conducted in 2018 and 2019 to determine the temporal effects of drought on canopy growth of winter wheat. Weekly UAS data were collected using red, green, and blue (RGB) and multispectral (MS) sensors over a yield trial consisting of 22 winter wheat cultivars in both irrigated and dryland environments. Raw-images were processed to compute canopy features such as canopy cover (CC) and canopy height (CH), and vegetation indices (VIs) such as Normalized Difference Vegetation Index (NDVI), Excess Green Index (ExG), and Normalized Difference Red-edge Index (NDRE). The drought was more severe in 2018 than in 2019 and the effects of growth differences across years and irrigation levels were visible in the UAS measurements. CC, CH, and VIs, measured during grain filling, were positively correlated with grain yield (r = 0.4–0.7, p < 0.05) in the dryland in both years. Yield was positively correlated with VIs in 2018 (r = 0.45–0.55, p < 0.05) in the irrigated environment, but the correlations were non-significant in 2019 (r = 0.1 to −0.4), except for CH. The study shows that high-throughput UAS data can be used to monitor the drought effects on wheat growth and productivity across the temporal and spatial domains.
Highlights
Wheat (Triticum aestivum L.) is the second most important crop in Texas, after cotton (Gossypium spp.), where it is produced under dryland and irrigated conditions for grain and forage
We studied the seasonal dynamics of canopy cover (CC), canopy height (CH), Normalized Difference Vegetation Index (NDVI), Excess Green Index (ExG), and Normalized Difference Rededge Index (NDRE) obtained from Unmanned Aerial System (UAS) to assess the effect of drought on winter wheat growth
Successful detection of phenological phases can be beneficial to wheat breeders to screen genotypes for respective traits. Detection of these phases can be helpful to assess the future drought impact on canopy growth and can support farmers to make management decisions. It needs further research and validation, this study showed the possibility of using multi-temporal UAS data collected over the entire season to estimate the time of phenological phases in winter wheat
Summary
Wheat (Triticum aestivum L.) is the second most important crop in Texas, after cotton (Gossypium spp.), where it is produced under dryland and irrigated conditions for grain and forage. The frequent occurrence of drought poses a threat to winter wheat production in this region and reduces the yield under both the dryland and irrigated conditions [2]. The historic drought of 2011 and 2012 reduced wheat yield in Texas to 1.2 Mt compared to the five-year average of 2.5 Mt per hectare [3]. Another drought episode followed in 2018 when precipitation dropped below. The frequent and unpredictable magnitude of drought observed this past decade reinforces the need to prepare for future climate threats
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