Evaluation of Grass Quality under Different Soil Management Scenarios Using Remote Sensing Techniques

Mohammad Sadegh Askari,Aidan Magee,Timothy Mccarthy,Darren J Murphy

doi:10.3390/rs11151835

Abstract

Hyperspectral and multispectral imagery have been demonstrated to have a considerable potential for near real-time monitoring and mapping of grass quality indicators. The objective of this study was to evaluate the efficiency of remote sensing techniques for quantification of aboveground grass biomass (BM) and crude protein (CP) in a temperate European climate such as Ireland. The experiment was conducted on 64 plots and 53 paddocks with varying quantities of nitrogen applied. Hyperspectral imagery (HSI) and multispectral imagery (MSI) were analyzed to develop the prediction models. The MSI data used in this study were captured using an unmanned aircraft vehicle (UAV) and the satellite Sentinel-2, while the HSI data were obtained using a handheld hyperspectral camera. The prediction models were developed using partial least squares regression (PLSR) and stepwise multi-linear regression (MLR). Eventually, the spatial distribution of grass biomass over plots and paddocks was mapped to assess the within-field variability of grass quality metrics. An excellent accuracy was achieved for the prediction of BM and CP using HSI (RPD > 2.5 and R2 > 0.8), and a good accuracy was obtained via MSI-UAV (2 < RPD < 2.5 and R2 > 0.7) for the grass quality indicators. The accuracy of the models calculated using MSI-Sentinel-2 was reasonable for BM prediction and insufficient for CP estimation. The red-edge range of the wavelengths showed the maximum impact on the predictability of grass BM, and the NIR range had the greatest influence on the estimation of grass CP. Both the PLSR and MLR techniques were found to be sufficiently robust for spectral modelling of aboveground BM and CP. The PLSR yielded a slightly better model than MLR. This study suggested that remote sensing techniques can be used as a rapid and reliable approach for near real-time quantitative assessment of fresh grass quality under a temperate European climate.

Highlights

Grasslands are the dominant land-cover type in Ireland and are the most productive agricultural lands in the world [1,2,3]
Aboveground grass biomass, which is usually measured as kilograms grass dry matter (DM) produced per hectare and crude protein (g kg−1 DM), are considered important indicators for assessing fresh grass quality (GQ) and the efficiency of fertilization management systems during the growing season [9]
The multispectral imagery (MSI)-Sentinel-2 had a lower spatial resolution (10 or 20 m) and a higher spectral resolution (10 bands used in this study) than MSI-unmanned aircraft vehicle (UAV)

Summary

Introduction

Grasslands are the dominant land-cover type in Ireland and are the most productive agricultural lands in the world [1,2,3]. Aboveground grass biomass, which is usually measured as kilograms grass dry matter (DM) produced per hectare (kg DM ha−1) and crude protein (g kg−1 DM), are considered important indicators for assessing fresh grass quality (GQ) and the efficiency of fertilization management systems during the growing season [9]. The differences in soil, topography, weather conditions, species composition, and management practices are the main reasons for GQ variation during the growing season [11,12]. To account for these variations, a large quantity of seasonal data is usually required for evaluating and mapping GQ indicators. Developing a non-destructive, rapid, and reliable approach for spatiotemporal modelling of fresh grass quantity and quality would make a substantial contribution to sustainable grassland management practices

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Discussion

Conclusion