Assessment of long-term management impact on soil C dynamics in subtropical grasslands

View the project final report

• 2012 annual report

Commodities

• Agronomic: grass (misc. perennial)
• Animals: bovine

Practices

• Crop Production: agroforestry, forestry
• Natural Resources/Environment: carbon sequestration
• Production Systems: agroecosystems
• Soil Management: organic matter, soil analysis

Grasslands are indispensable for livestock productivity and profitability, and they serve critical ecological functions, including terrestrial carbon (C) sequestration, greenhouse gas and climate change mitigation. In past century, population-induced changes in demand for food has promoted the adoption of intensive grassland management aimed at increasing crop and animal production. However, there is a pressing need to balance productivity with long-term sustainability of ecosystems, especially in grasslands where most (~90%) of the ecosystem carbon (C) is allocated to below-ground reserves, and intensification can significantly alter soil C dynamics, hamper grassland's ability to carry the livestock population that they support, and severely erode its ecological functionality. Very limited knowledge exists on the dynamics of soil C in the Southeastern USA where characteristic high temperature and moisture, flat topography, and sandy composition of the soils favor rapid decomposition of soil organic matter and leaching of organic compounds. Hence, it is uncertain if intensive management which favors higher above-ground production and animal production will have long-term effect on soil C dynamics, compared to low-input management systems such as native rangelands. This research will be conducted on established (>20 years) experimental sites in Florida to quantify the long-term impacts of 3 levels of management intensity (intensively cultivated pasture, silvo-pasture, and native rangeland) on soil C stocks, allocation of below- and above-ground biomass, and losses through CO2 efflux. Outcomes of this study are expected to have important implications for management and policy-making decisions, in favor of balancing increased productivity with sustainability in grasslands ecosystems.

This research will be conducted to

i. Quantify soil total organic C and particulate organic C under 3 distinct management systems by sampling and analyzing soil samples from each >20 year old field. This will be conducted to draw inferences on the long-term sequestration of carbon under the different established management systems.
ii. Assess for differences in the contribution of above- and below-ground components under the 3 distinct management systems by quantifying the above- and below-ground biomass. This will provide needed knowledge on mechanism of C sequestration under each management system based on significant shifts in the allocation of biomass as management intensity increases.
iii. Determine the long-term rate of C loss in form of CO2 efflux across seasons under each management system. This will foster a deeper knowledge on the contribution of autotrophic and heterotrophic respiration to soil C losses under the distinct management systems.