Abstract
Dryland pastures provide the basis for animal sustenance in extensive production systems in Iberian Peninsula. These systems have temporal and spatial variability of pasture quality resulting from the diversity of soil fertility and pasture floristic composition, the interaction with trees, animal grazing, and a Mediterranean climate characterized by accentuated seasonality and interannual irregularity. Grazing management decisions are dependent on assessing pasture availability and quality. Conventional analytical determination of crude protein (CP) and fiber (neutral detergent fiber, NDF) by reference laboratory methods require laborious and expensive procedures and, thus, do not meet the needs of the current animal production systems. The aim of this study was to evaluate two alternative approaches to estimate pasture CP and NDF, namely one based on near-infrared spectroscopy (NIRS) combined with multivariate data analysis and the other based on the Normalized Difference Vegetation Index (NDVI) measured in the field by a proximal active optical sensor (AOS). A total of 232 pasture samples were collected from January to June 2020 in eight fields. Of these, 96 samples were processed in fresh form using NIRS. All 232 samples were dried and subjected to reference laboratory and NIRS analysis. For NIRS, fresh and dry samples were split in two sets: a calibration set with half of the samples and an external validation set with the remaining half of the samples. The results of this study showed significant correlation between NIRS calibration models and reference methods for quantifying pasture quality parameters, with greater accuracy in dry samples (R2 = 0.936 and RPD = 4.01 for CP and R2 = 0.914 and RPD = 3.48 for NDF) than fresh samples (R2 = 0.702 and RPD = 1.88 for CP and R2 = 0.720 and RPD = 2.38 for NDF). The NDVI measured by the AOS shows a similar coefficient of determination to the NIRS approach with pasture fresh samples (R2 = 0.707 for CP and R2 = 0.648 for NDF). The results demonstrate the potential of these technologies for estimating CP and NDF in pastures, which can facilitate the farm manager’s decision making in terms of the dynamic management of animal grazing and supplementation needs.
Highlights
IntroductionNatural or improved dryland pastures provide the basis of animal sustenance in extensive production systems in Portugal [1]
The results of this study showed a significant correlation between near-infrared spectroscopy (NIRS) calibration models or Normalized Difference Vegetation Index (NDVI) obtained by optical proximal sensing and reference methods for quantifying pasture crude protein and fiber
The most accurate indicators were obtained with NIRS models applied to pasture samples that had undergone a drying and screening process (R2 = 0.936 for crude protein (CP) and R2 = 0.914 for neutral detergent fiber (NDF))
Summary
Natural or improved dryland pastures provide the basis of animal sustenance in extensive production systems in Portugal [1]. The scarcity of pastures and the decrease in their quality may even extend into the autumn–winter months in dryer years [3]. This temporal (i.e., seasonal) variability resulting from climatic seasonality is compounded by an important spatial variability (i.e., within or between fields) [4], which is a consequence of the different fertility of the soils, the diversity of the floristic composition of the pastures and the influence of AgriEngineering 2021, 3, 73–91.
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