Investigating Ecosystem-Scale Responses to Compost Amendments in a Grazed Grassland

Abstract

Compost amendments to rangelands is a proposed nature-based climate solution to increase plant productivity and soil carbon sequestration. However, it has not been evaluated using semi-continuous ecosystem-scale measurements. Here we present the first study to utilize eddy covariance and footprint partitioning to monitor carbon exchange in a grassland with and without compost amendment, monitoring for one year before and one year after treatment. Compost amendments to an annual California grassland were found to enhance net ecosystem removal of C. Our study confirmed that compost-amended grasslands, similar to non-amended grasslands, are net carbon sources to the atmosphere; however amendments appear to be slowing down the rate at which these ecosystems lose carbon by 0.71 Mg C ha-1 per growing season. Digital repeated imagery of the canopy revealed that compost-amended grasslands experienced an earlier green-up, resulting in an overall longer growing season by more than 30 days. Scale-emergent processes such as changes in phenology are understudied in nature-based climate solutions and need to be better investigated before widespread adoption. Notably, we did not detect significantly higher amounts of soil C in compost-amended soils. High variability in soil C demands greater sampling replication in future studies. A longer growing season and higher productivity are hypothesized to be a result of greater availability of macro and micronutrients in the top layer of soil (specifically N, P and Zn).

Spatial and temporal variability in soil and vegetation carbon dynamics under experimental drought and soil amendments

“…In addition, the significant increase in aboveground biomass three years after the compost application indicate the persistence of favorable plant growing conditions, such as increased N in the soil. These results are in accordance with Fenster et al (2023), who found that the benefits of compost treatments on the ecosystem C balance of grasslands one year after application were manifested as extended growing season, and thus potentially higher plant productivity, rather than as an increase in net soil C. This also stresses the importance of including vegetation dynamics when assessing the effectiveness of C management.…”