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Retrieval of crude protein in perennial ryegrass using spectral data at the canopy level


Togeiro de Alckmin, G and Lucieer, A and Roerink, G and Rawnsley, R and Hoving, I and Kooistra, L, Retrieval of crude protein in perennial ryegrass using spectral data at the canopy level, Remote Sensing, 12, (18) Article 2958. ISSN 2072-4292 (2020) [Refereed Article]

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Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons 4.0 International (CC BY 4.0) license (

DOI: doi:10.3390/rs12182958


Crude protein estimation is an important parameter for perennial ryegrass (Lolium perenne) management. This study aims to establish an effective and affordable approach for a non-destructive, near-real-time crude protein retrieval based solely on top-of-canopy reflectance. The study contrasts different spectral ranges while selecting a minimal number of bands and analyzing achievable accuracies for crude protein expressed as a dry matter fraction or on a weight-per-area basis. In addition, the model’s prediction performance in known and new locations is compared. This data collection comprised 266 full-range (350–2500 nm) proximal spectral measurements and corresponding ground truth observations in Australia and the Netherlands from May to November 2018. An exhaustive-search (based on a genetic algorithm) successfully selected band subsets within different regions and across the full spectral range, minimizing both the number of bands and an error metric. For field conditions, our results indicate that the best approach for crude protein estimation relies on the use of the visible to near-infrared range (400–1100 nm). Within this range, eleven sparse broad bands (of 10 nm bandwidth) provide performance better than or equivalent to those of previous studies that used a higher number of bands and narrower bandwidths. Additionally, when using top-of-canopy reflectance, our results demonstrate that the highest accuracy is achievable when estimating crude protein on its weight-per-area basis (RMSEP 80 kg.ha−1). These models can be employed in new unseen locations, resulting in a minor decrease in accuracy (RMSEP 85.5 kg.ha−1). Crude protein as a dry matter fraction presents a bottom-line accuracy (RMSEP) ranging from 2.5–3.0 percent dry matter in optimal models (requiring ten bands). However, these models display a low explanatory ability for the observed variability (R2 > 0.5), rendering them only suitable for qualitative grading.

Item Details

Item Type:Refereed Article
Keywords:perennial ryegrass, hyperspectral, machine learning, crude protein, partial least squares, feature selection, variable importance
Research Division:Engineering
Research Group:Geomatic engineering
Research Field:Photogrammetry and remote sensing
Objective Division:Animal Production and Animal Primary Products
Objective Group:Pasture, browse and fodder crops
Objective Field:Sown pastures (excl. lucerne)
UTAS Author:Togeiro de Alckmin, G (Mr Gustavo Togeiro de Alckmin)
UTAS Author:Lucieer, A (Professor Arko Lucieer)
UTAS Author:Rawnsley, R (Dr Richard Rawnsley)
ID Code:148021
Year Published:2020
Web of Science® Times Cited:3
Deposited By:Geography and Spatial Science
Deposited On:2021-11-30
Last Modified:2022-01-14
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