Does Grazing Affect Soil Carbon in Subtropical Humid Seminatural Grasslands?

Rangelands account for a large portion of global carbon stocks and have high potential for carbon sequestration if managed properly. Grazing has variable effects on soil organic carbon depending on climate, geography, and soil type; therefore, grazers in various regions may need to be managed differently to ensure optimum carbon sequestration. This study aimed to assess the impacts of cattle grazing on soil carbon in seminatural subtropical humid rangelands in Florida. We measured root biomass, bulk density, soil organic carbon (SOC), and total carbon (TC) concentrations and used the equivalent soil mass method to assess organic carbon stock (OCS) and total carbon stock at three depths (0-5 cm, 5-15 cm, and 15-30 cm) inside and outside of five 15-yr-old grazing exclosures. We also surveyed the vegetation at each sampling location and litter biomass inside and outside of exclosures. We found that grazing increased bulk density, decreased root biomass, but did not affect litter amount. SOC and TC concentrations did not differ significantly between ungrazed and grazed plots. On an equivalent soil mass basis, we found greater soil carbon stocks in grazed plots within the shallower part of the soil (0-5 cm). Removal of grazing resulted in a clear difference in vegetation composition between grazed and ungrazed plots, with grazed plots having higher grass cover (on average 60% in grazed vs. 13% in ungrazed) and ungrazed having higher forb cover (on average 78% in ungrazed vs. 32% in grazed). Results provide evidence that grazing increased soil carbon stocks in the top layer of soil, but longer-term studies are needed to assess the impact of grazing on SOC concentrations. To further clarify the impact of grazing on drivers of soil carbon in subtropical humid seminatural grasslands, we recommend further study of grazing impacts on productivity, root production and turnover, and microbial responses. (C) 2021 The Society for Range Management. Published by Elsevier Inc. All rights reserved.

Automated summary

This study assessed the impacts of cattle grazing on soil carbon in seminatural subtropical humid rangelands in Florida. The results showed that grazing increased soil carbon stocks in the top layer of soil, decreased root biomass, but did not affect litter amount. There were no significant differences in SOC and TC concentrations between grazed and ungrazed plots.