266. Satellite-derived Assessment of Seasonal Forage Dynamics in Bermudagrass Pastures Under Different Management Strategies.

Abstract This study aimed to evaluate the seasonal variation of forage mass in bermudagrass pastures managed under different strategies using satellite time-series analysis. The research was conducted at the Texas A&M AgriLife Research and Extension Center in Overton, Texas, from 2019 to 2024, across three management areas, comprised of pastures of ‘Coastal’ or common bermudagrass (BG) overseeded with either ‘Apache’ arrowleaf clover without N fertilization or ‘Nelson’ annual ryegrass plus N fertilization (area 1), pastures of ‘Tifton 85’ BG (area 2), and pastures of BG sod-seeded with ‘Maton Rye’ and ‘Nelson’ annual ryegrass (area 3). A predictive model of forage biomass (FM) was developed using pasture forage samples combined with spectral and vegetation indices from Sentinel-2 imagery processed in Google Earth Engine, along with meteorological data. The optimal model was applied to a 2019–2024 Sentinel-2 time series, and a Savitzky–Golay smoothing filter (window_length = 15, polyorder = 3) was used to derive monthly FM. Data were analyzed using a repeated-measures framework with month as the repeated factor within each year. A generalized estimating equation assuming an autoregressive [AR(1)] correlation structure was fitted, including fixed effects of management, month, and their interaction, with robust standard errors. A linear mixed-effects model with random intercepts for year and plot accounted for hierarchical variability. Significant (P < 0.001) management × month interactions indicated distinct seasonal growth patterns. Overall, FM increased from late winter to early summer, peaking between May and July, before declining toward autumn. Management strategies containing cool-season species exhibited greater early-season production, whereas warm-season bermudagrass pastures peaked later in the season, with BG + clover pastures reaching maximum production approximately one month earlier than BG + ryegrass (P < 0.05). Winter pastures (rye + ryegrass) produced the greatest forage mass from February through April (P < 0.01), exceeding both BG + clover and BG + ryegrass during this interval, but declined rapidly after May as warm-season species dominated. Adjacent-month contrasts confirmed significant (P < 0.05) transitions during March–April and June–July, indicating periods of rapid accumulation and subsequent senescence. Variance components for plot and year were small, confirming consistent seasonal trends across management areas. These results demonstrate the ability of satellite-based models to capture biologically meaningful temporal variation and identify complementary seasonal production among forage systems.