Long-Term Soil Carbon Sequestration Under Subtropical Grassland Management Systems.

Grasslands are indispensable for livestock productivity and profitability, and they serve critical ecological functions. However, population-driven intensified production can significantly alter soil C dynamics, hamper grassland's ability to carry the livestock population that they support, and severely erode its ecological functionality. This research was conducted on established (>20 years) experimental sites at UF-IFAS Range Cattle REC, Ona, Florida to quantify the long-term impacts of 3 management systems (intensively managed improved pasture – Improved-P, Pine-Bahia silvopasture – Silvo-P, and native rangelands – Native-R) on total soil carbon (TC), <53μm- sized particulate organic carbon (POC) fraction – a slow C pool, and >53μm-sized mineral fraction (Cmin) – a labile C pool . Based on a comparative-mensurative experimental design, 150 sample soil cores were collected from six collocated ~6ha fields (2 replicate per site) at 3 soil depth increments (0 to 10, 10 to 20, and 20 to 30cm), and analyzed for TC, POC, and Cmin. Results showed that all sites sequestered comparable TC, POC, and Cmin at 0-10cm (P>0.05). At 10-20cm, Improved-P and Silvo-P sites sequestered similar TC, POC, and Cmin, but Native-R showed significantly lower TC (9Mg Ha^-1, P=0.005) relative to Improved-P (16Mg ha^-1) and Silvo-P (16Mg ha^-1), lower POC (2Mg ha^-1, P<0.0001) relative to Silvo-P (10Mg ha^-1), and lower Cmin (7Mg ha^-1, P<0.0001) relative to Improved-P (13Mg ha^-1). At 20-30cm, the TC sequestered in Silvo-P (13Mg ha^-1) is comparable to Improved-P (11Mg ha^-1), and significantly differs from Native-R (7Mg ha^-1), but Improve-P and Native-R are not significantly different. This study shows that, under subtropical conditions, long-term management has pronounced impacts on soil C (10-30 cm depth) and suggests that integrated management systems such as Silvo-P may be more beneficial for stable carbon sequestration. This study may guide management and policy-making decisions toward balancing increased productivity with sustainability in grasslands ecosystems.