A Lifecycle Model to Evaluate Carbon Sequestration Potential and Greenhouse Gas Dynamics of Managed Grasslands

Abstract

Soil amendments can increase net primary productivity (NPP) and soil carbon (C) sequestration in grasslands, but the net greenhouse gas fluxes of amendments such as manure, compost, and inorganic fertilizers remain unclear. To evaluate opportunities for climate change mitigation through soil amendment applications, we designed a field-scale model that quantifies greenhouse gas emissions (CO 2 , CH 4 , and N 2 O) from the production, application, and ecosystem response of soil amendments. Using this model, we developed a set of case studies for grazed annual grasslands in California. Sensitivity tests were performed to explore the impacts of model variables and management options. We conducted Monte Carlo simulations to provide estimates of the potential error associated with variables where literature data were sparse or spanned wide ranges. In the base case scenario, application of manure slurries led to net emissions of 14 Mg CO 2 e ha -1 over a 3-year period. Inorganic N fertilizer resulted in lower greenhouse gas emissions than the manure (3 Mg CO 2 e ha -1 ), assuming equal rates of N addition and NPP response. In contrast, composted manure and plant waste led to large offsets that exceeded emissions, saving 23 Mg CO 2 e ha -1 over 3 years. The diversion of both feedstock materials from traditional high-emission waste management practices was the largest source of the offsets; secondary benefits were also achieved, including increased plant productivity, soil C sequestration, and reduced need for commercial feeds. The greenhouse gas saving rates suggest that compost amendments could result in significant offsets to greenhouse gas emissions, amounting to over 28 MMg CO 2 e when scaled to 5% of California rangelands. We found that the model was highly sensitive to manure and landfill management factors and less dependent on C sequestration, NPP, and soil greenhouse gas effluxes. The Monte Carlo analyses indicated that compost application to grasslands is likely to lead to net greenhouse gas offsets across a broad range of potential environmental and management conditions. We conclude that applications of composted organic matter to grasslands can contribute to climate change mitigation while sustaining productive lands and reducing waste loads.

Digging deeper: A holistic perspective of factors affecting soil organic carbon sequestration in agroecosystems

“…There are also several models available to measure gaseous fluxes of soil (DeLonge, Ryals, & Silver, ), and gaseous fluxes are strongly impacted by SOC content and stock. Furthermore, the cost and precision of measuring changes in soil C stocks and fluxes must be assessed at different scales (Mäkipää, Hakkinen, Muukkonen, & Peltoniemi, ).…”

What Agriculture Can Learn from Native Ecosystems in Building Soil Organic Matter: A Review

“…This is perfectly fine if the goal is to subsidize the fertility of a farm, but not helpful if the goal is net sequestration of atmospheric CO 2 . Exceptions may exist where applications of composted materials prevent the disposal of organic wastes in landfills or slurry ponds, thus avoiding the production of more potent greenhouse gases methane and nitrous oxide [73]. The addition of composted materials to croplands will increase SOM on those lands directly, and often indirectly by increasing crop productivity and associated belowground inputs of organic matter.…”

Long‐term climate change mitigation potential with organic matter management on grasslands

“…Organic matter amendments add C directly to the soil, some of which may remain in stable pools (Lynch et al 2005, Cabrera et al 2009, Ryals et al 2014. Moreover, organic matter amendments can contribute to greenhouse gas offsets such as avoided methane (CH 4 ) emissions from the diversion of organic wastes from landfills or slurry ponds (DeLonge et al 2013).…”