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Research article - Peer-reviewed, 2022

Estimation of biomass and nutritive value of grass and clover mixtures by analyzing spectral and crop height data using chemometric methods

Sun, Sashuang; Zuo, Zhiyu; Yue, Wenjun; Morel, Julien; Parsons, David; Liu, Jian; Peng, Junxiang; Cen, Haiyan; He, Yong; Shi, Jiang; Li, Xiaolong; Zhou, Zhenjiang

Abstract

The study aims to estimate forage yield and quality parameters by fusing field spectroscopy data and crop height with regression-based mathematical models. Field experiments were carried out to obtain canopy spectral reflectance (CSR) of grass and clover mixtures. Additionally, grass height (Hgrass) and clover height (Hclover) were used as auxiliary explanatory variables with CSR to estimate forage yield and quality. Variable importance in projection (VIP) was utilized for sensitive wavelength selection. Two chemometric methods, namely partial least squares regression (PLSR) and support vector machine (SVM), were implemented to build models using full spectra and sensitive wavelengths for estimating dry matter yield (DMY), in vitro true digestibility (IVTD), neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), acid detergent fiber (ADF), acid detergent lignin (ADL), crude protein (CP), crude protein yield (CPY), and botanical composition (BC). Of the total 235 samples, 157 samples were randomly selected for model calibration while the remaining 78 samples were used for model validation. Results showed that both PLSR and SVM could reasonably estimate forage yield and quality variables, although performances of PLSR were more stable in terms of R2 and relative root mean square error (RRMSE) for both calibration and validation. Prediction performances of models using only full spectra data (PLSRspec) and models also using crop height information (PLSRspec+H) as model inputs were compared in this study. PLSRspec+H presented higher R2 and lower RRMSE than PLSRspec models (e.g. R2 improved from 0.83 to 0.90 for NDF and from 0.56 to 0.73 for IVTD, and RRMSE decreased from 8.14% to 6.58% for NDF and from 2.55% to 2.02% for IVTD). In addition, PLSR that used sensitive wavelengths and crop height (PLSRwave+H) as model inputs also had good performance, although slightly worse than PLSRspec+H. The results suggest that there is good potential to predict forage biomass and nutritive value by combining spectral and height variables with chemometric methods.

Keywords

forage crop; field spectroscopy; crop height; partial least squares regression; support vector machine; yield and quality

Published in

Computers and Electronics in Agriculture
2022, Volume: 192, article number: 106571

      SLU Authors

    • Morel, Julien

      • Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences
      • Parsons, David

        • Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences
        • Peng, Junxiang

          • Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences

        UKÄ Subject classification

        Agricultural Science

        Publication identifier

        DOI: https://doi.org/10.1016/j.compag.2021.106571

        Permanent link to this page (URI)

        https://res.slu.se/id/publ/114998