Rapid mapping of winter wheat yield, protein, and nitrogen uptake using remote and proximal sensing

Authors: WANG, KU - Washington State University; Huggins, David; TAO, HAIYING - Washington State University

Submitted to: International Journal of Applied Earth Observation and Geoinformation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2019
Publication Date: 10/1/2019
Citation: Wang, K., Huggins, D.R., Tao, H. 2019. Rapid mapping of winter wheat yield, protein, and nitrogen uptake using remote and proximal sensing. International Journal of Applied Earth Observation and Geoinformation. Vol.23. https://doi.org/10.1016/j.jag.2019.101921.
DOI: https://doi.org/10.1016/j.jag.2019.101921

Interpretive Summary: Farmers’ interest in precision nitrogen (N) fertilization has grown in the inland Pacific Northwest due to the occurance of large field variations in grain yield and protein content of wheat. Mapping the spatial variability of yield, protein content, and total grain N uptake can be a useful tool for post-harvest evaluation of N sufficiency that, in turn, can guide N fertilization. We evaluated the use of satellite imagery with field topographic variables to assess winter wheat yield, protein content, and N uptake. We found that the combination of satellite imagery and topographic variables were useful for explaining field variations in wheat yield and N uptake. We concluded that combining satellite imagery with field topographical factors shows great potential for accurately and efficiently estimating winter wheat yield and Ng, which can help guide N fertilizer management. These results will be useful for farmers, NRCS and scientists interested in evaluating cropping system effects on the potential for wind erosion. vegetation index (NDVI), the normalized difference red edge index (NDRE), terrain curvature, slope, aspect, topographic wetness index, and solar radiation are the most relevant co-variables that contribute to spatial variability of yield and Ng. Yield and Ng exhibited strong relationships with NDVI and NDRE from late June through early July during grain filling stage, with nearly all R2 > 0.6. We found greater yield and Ng values in concave-shaped terrain; 0-5° and 10-20° slopes; and flat, eastern, or northern aspects. In contrast, protein content exhibited weak relationships with vegetation indices and nearly all terrain factors. Prediction models demonstrated that these variables can provide good estimations of yield and Ng, with R2 of 0.848 and 0.864, respectively, and RMSE of 48.47 and 0.0136, respectively. Combining RapidEye-based NDRE with proximal sensor-based topographical factors shows great potential for accurately and efficiently estimating winter wheat yield and Ng, which can help guide N fertilizer management. Interpretive Summary (peer reviewed journal/first formal report only): Farmers’ interest in precision nitrogen (N) fertilization has grown in the inland Pacific Northwest due to the occurance of large field variations in grain yield and protein content of wheat. Mapping the spatial variability of yield, protein content, and total grain N uptake can be a useful tool for post-harvest evaluation of N sufficiency that, in turn, can guide N fertilization. We evaluated the use of satellite imagery with field topographic variables to assess winter wheat yield, protein content, and N uptake. We found that the combination of satellite imagery and topographic variables were useful for explaining field variations in wheat yield and N uptake. We concluded that combining satellite imagery with field topographical factors shows great potential for accurately and efficiently estimating winter wheat yield and Ng, which can help guide N fertilizer management. These results will be useful for farmers, NRCS and scientists interested in evaluating cropping system effects on the potential for wind erosion.

Technical Abstract: Farmers’ interest in precision nitrogen (N) fertilization of wheat has grown in the inland Pacific Northwest due to significant within-field spatial variability in yield and protein content. Mapping the spatial variability of yield, protein content, and total grain N uptake (Ng) can be a useful tool for post-harvest evaluation of N sufficiency that, in turn, can guide precision N fertilization. We evaluated the applicability of combining RapidEye satellite imagery-derived vegetation indices with topographic variables derived from high-resolution data obtained from proximal sensors to estimate winter wheat yield, protein content, and Ng. Results indicate that the normalized difference vegetation index (NDVI), the normalized difference red edge index (NDRE), terrain curvature, slope, aspect, topographic wetness index, and solar radiation are the most relevant co-variables that contribute to spatial variability of yield and Ng. Yield and Ng exhibited strong relationships with NDVI and NDRE from late June through early July during grain filling stage, with nearly all R2 > 0.6. We found greater yield and Ng values in concave-shaped terrain; 0-5° and 10-20° slopes; and flat, eastern, or northern aspects. In contrast, protein content exhibited weak relationships with vegetation indices and nearly all terrain factors. Prediction models demonstrated that these variables can provide good estimations of yield and Ng, with R2 of 0.848 and 0.864, respectively, and RMSE of 48.47 and 0.0136, respectively. Combining RapidEye-based NDRE with proximal sensor-based topographical factors shows great potential for accurately and efficiently estimating winter wheat yield and Ng, which can help guide N fertilizer management.