Using Structure-from-Motion to estimate cover crop biomass and characterize canopy structure

Authors: DOBBS, APRIL - North Carolina State University; GINN, DANIEL - Texas A&M University; SKOVSEN, SOREN - Aarhus University; YADAV, RAMAWATAR - Iowa State University; JHA, PRASHANT - Iowa State University; BAGAVATHIANNAN, MUTHUKUMAR - Texas A&M University; Mirsky, Steven; REBERG-HORTON, S\CHRIS - North Carolina State University; LEON, RAMON - North Carolina State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2023
Publication Date: 9/1/2023
Citation: Dobbs, A.M., Ginn, D., Skovsen, S., Yadav, R., Jha, P., Bagavathiannan, M.V., Mirsky, S.B., Reberg-Horton, S.S., Leon, R.G. 2023. Using Structure-from-Motion to estimate 302:109099. cover crop biomass and characterize canopy structure. Field Crops Research. https://doi.org/10.1016/j.fcr.2023.109099.
DOI: https://doi.org/10.1016/j.fcr.2023.109099

Interpretive Summary: Cover crops need to reliably produce a large amount of biomass in order to reliably suppress weeds. Farmers struggle to use cover crops for weed control because of variability in cover crop biomass production and they have no good way to easily estimate cover crop biomass. This study assessed the use of cameras and the Structure from Motion technique to estimate cereal rye and wheat biomass in North Carolina, Iowa, and Maryland and also collected crop height, leaf area index, and photosynthetically active radiation. Biomass was positively related to crop height for both rye and wheat; leaf area index was positively related to both cover crop biomass and height. When crop height was used in conjunction with Structure from Motion data points, we successfully estimated biomass through levels of 8000 kg biomass ha-1. The Structure from Motion methodology provided a more accurate estimation of biomass than canopy height alone by capturing species-level differences in canopy structure. This work will aid farmers through the incorporation of results into tools that help farmers to better manage their cover crops to meet goals such as weed control.

Technical Abstract: Variability in biomass production poses a challenge for growers when using cover crops for weed control. However, most methods for assessing cover crop biomass are laborious and impractical on a field scale. The present study evaluated the use of Structure-from-Motion (SfM) photogrammetry to estimate biomass in cereal rye (Secale cereale L.) and winter wheat (Triticum aestivum L.). SfM point clouds were generated from RGB videos taken over crop fields in North Carolina, Iowa, and Maryland, USA, throughout two growing seasons. Crop height, leaf area index (LAI), and photosynthetically active radiation (PAR) were also measured. Biomass was positively related to crop height for both rye (R2 = 0.621) and wheat (R2 = 0.55). LAI was positively related to biomass accumulation and crop height for both species, increasing linearly in rye and exponentially in wheat. Conversely, PAR penetration below the canopy decreased with biomass accumulation and crop height in both species, with more rapid extinction in wheat than rye. Point cloud pixel density showed a positive linear relationship with biomass in rye but saturated after 2,500 kg ha-1. In wheat, point cloud pixel density was weakly and negatively related to biomass due to a denser canopy causing faster saturation of tissue detection by SfM point clouds. However, crop height integrated with point cloud density had a positive relationship with biomass through levels of 8000 kg ha-1. When models were validated with independent data, predicted and measured biomass were positively related for both rye (R2 = 0.859) and wheat (R2 = 0.781). Based on the results, SfM provided a more accurate estimation of biomass than canopy height alone by capturing species-level differences in canopy architecture.