Print PageApplication of organic matter amendments to soils has been proposed as a means to increase soil carbon (C) sequestration and offset greenhouse gas emissions. There are many variables that can affect the source or sink strength of this practice. To date, few comparisons have explored the relative impacts of organic matter amendments with other common practices. In this study, we developed a field-scale life cycle assessment (LCA) model to investigate the potential for organic matter amendments to sequester soil C and offset greenhouse gas emissions. The LCA was parameterized for grazed annual California grasslands using field observations and literature values. The model includes carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions and offsets from amendment production, application, and ecosystem response. We evaluated the LCA for scenarios using applications of compost, manure, and inorganic nitrogen (N) fertilizer. Sensitivity analyses were performed on several parameters, particularly those considered to be most uncertain.
Results/Conclusions
For our scenarios, offsets associated with compost application exceeded emissions, leading to a net offset of > 20 Mg CO2e ha-1. In comparison, application of slurry-pond manure led to net emissions of approximately 20 Mg CO2e ha-1. Nitrogen fertilization led to lower emissions (< 5 Mg CO2e ha-1) when assuming similar ecosystem benefits per kg N, but did not contribute to waste management. Scaling up, annual compost application to areas equal to 5 % of California’s rangeland could offset the annual statewide emissions of the agriculture and forestry sectors (> 28 MMg CO2e, CA ARB 2009). The offset is sensitive to variables such as compost composition, manure management, and local landfill characteristics. Results were less sensitive to C sequestration, enhanced NPP, soil greenhouse gas emissions, and transportation. Findings suggest that compost application to rangelands may contribute to climate change mitigation.
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