Rapeseed seedling stand counting and seeding performance evaluation at two early growth stages based on unmanned aerial vehicle imagery

Authors: ZHAO, BIQUAN - Huazhong Agricultural University; ZHANG, JIAN - Huazhong Agricultural University; Yang, Chenghai; ZHOU, GUANGSHENG - Huazhong Agricultural University; DING, YOUCHUN - Huazhong Agricultural University; YEYIN, SHI - University Of Nebraska; ZHANG, DONGYAN - Anhui Agricultural University; XIE, JING - Huazhong Agricultural University; LIAO, QINGXI - Huazhong Agricultural University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2018
Publication Date: 12/29/2018
Citation: Zhao, B., Zhang, J., Yang, C., Zhou, G., Ding, Y., Yeyin, S., Zhang, D., Xie, J., Liao, Q. 2018. Rapeseed seedling stand counting and seeding performance evaluation at two early growth stages based on unmanned aerial vehicle imagery. Frontiers in Plant Science. 9:1362. https://doi.org/10.3389/fpls.2018.01362.
DOI: https://doi.org/10.3389/fpls.2018.01362

Interpretive Summary: Crop seedling stand count in early growth stages is important not only for determining plant emergence, but also for planning other field operations. This study developed practical and rapid remote sensing methods for rapeseed stand counting and for evaluation of mechanical seeding performance. High resolution images were acquired of a rapeseed field at two early growth stages using an unmanned aerial vehicle (UAV) and were processed using image analysis and statistical techniques to identify rapeseed plants and estimate seedling counts. Results showed that the methods used were able to accurately estimate the total number of rapeseed plants and identify areas of failed germination. The UAV-based remote sensing methods can be useful for rapeseed seedling stand counting and for mechanical seeding performance evaluations.

Technical Abstract: The development of unmanned aerial vehicles (UAVs) and image processing algorithms for field-based phenotyping offers a non-invasive and effective technology to obtain plant growth traits such as canopy cover and plant height in fields. Crop seedling stand count in early growth stages is important not only for determining plant emergence, but also for planning other related agronomic practices. The main objective of this research was to develop practical and rapid remote sensing methods for early growth stage stand counting to evaluate mechanically seeded rapeseed (Brassica napus L.) seedlings. Rapeseed was seeded in a field by three different seeding devices. A digital single-lens reflex camera was installed on an UAV platform to capture ultrahigh resolution RGB images at two growth stages when most rapeseed plants had at least two leaves. Rapeseed plant objects were segmented from images of vegetation indices using typical Otsu thresholding method. After segmentation, shape features such as area, length-width ratio and elliptic fit were extracted from the segmented rapeseed plant objects to establish regression models of seedling stand count. Three row characteristics (the coefficient of variation of row spacing uniformity, the error rate of the row spacing and the coefficient of variation of seedling uniformity) were further calculated for seeding performance evaluation after crop row detection. Results demonstrated that shape features had strong correlations with ground-measured seedling stand count. The regression models achieved R-squared values of 0.845 and 0.867, respectively, for the two growth stages. The mean absolute errors of total stand count were 9.79% and 5.11% for the two respective stages. A single model over these two stages had an R-squared value of 0.846, and the total number of rapeseed plants was also accurately estimated with an average relative error of 6.83%. Moreover, the calculated row characteristics were demonstrated to be useful in recognizing areas of failed germination possibly resulted from skipped or ineffective planting. In summary, this study developed practical UAV-based remote sensing methods and demonstrated the feasibility of using the methods for rapeseed seedling stand counting and mechanical seeding performance evaluation at early growth stages.