121 Assessment of pasture sustainability using satellite time series analysis: a study on bermudagrass overseeded with clover or ryegrass under different stocking rates.

Abstract Understanding forage biomass dynamics is crucial for optimizing grazing management and enhancing the sustainability of livestock production systems. This study evaluated the variability of annual aboveground biomass (AGB) forage in pastures managed under different strategies, utilizing satellite time series analysis as a sustainability indicator. The research occurred at the Texas A&M AgriLife Research and Extension Center in Overton, Texas, from 2019 to 2024. Pastures included ‘Coastal’ and common bermudagrass (Cynodon dactylon (L.) Pers.) overseeded with either ‘Apache’ arrowleaf clover (Trifolium vesiculosum Savi.) without N fertilization or annual ryegrass (Lolium multiflorum Lam.) plus N fertilization. These pastures were managed under high, medium, and low forage mass for stocking rates (SR). A model was developed to predict AGB using pasture forage samples and spectral and vegetation indices derived from Sentinel-2 satellite images processed via Google Earth Engine (GEE). The optimal model was then applied to a Sentinel-2 time series from 2019 to 2024. For each year and pasture, the area under the curve (AUC) of accumulated forage mass was calculated using the spline method and divided by the timeframe (days) to derive an annual AGB forage index (g/m²). A trend line based on the linear regression between year and AGB forage was performed, where the slope represents the balance of AGB forage over the years. This metric served as a sustainability proxy, reflecting the variability of forage stock under different management strategies. Interestingly, pastures under high SR generally exhibited higher AGB forage than those under medium and low SR (Table 1). This outcome challenges the common assumption that reduced grazing pressure improves forage accumulation. Among the different pasture systems, Coastal bermudagrass outperformed common bermudagrass regarding AGB forage, particularly when overseeded with ryegrass. Considerable year-to-year variability in AGB forage was observed, likely influenced by climatic conditions. Despite these fluctuations, AGB forage showed a general trend towards stability over the study period, regardless of management practices. Notably, both Coastal and common bermudagrass overseeded with clover under medium SR showed a significant upward trend in AGB forage (Slope = 14.12 and 7.31 g/m2/year, P = 0.04 and 0.09, Table 1), suggesting improved forage accumulation with moderate grazing pressure. This study highlights the value of satellite-based time series analysis for predicting and assessing forage mass under grazing systems. The positive trends observed in medium SR systems with clover and high SR systems with ryegrass underscore the importance of balancing grazing intensity with forage regrowth potential. By integrating remote sensing technology and grazing management insights, this study provides a valuable framework for assessing and improving the sustainability of forage production systems.