Evaluating the contribution of soil organic carbon to improved water-holding capacity through increased compaction resistance

Climate change, extreme weather events, and soil degradation all mean that we are increasingly asking our soils to do more with less – infiltrate and store more water with less organic matter and weaker soil structure. A recent focus on soil health provides the opportunity to reverse this trend, but it will require a sound understanding of the expected benefits with potential changes to management practices and soil properties. It is generally agreed that increases in soil organic carbon (SOC) can result in both modest increases in plant available water (PAW) and greater resistance to compaction, yet key knowledge gaps remain: 1) the relative importance of the direct contribution of SOC to PAW vs. the indirect contribution through soil structure, and 2) the extent to which SOC indirectly augments the modest increases in PAW through greater resistance to soil compaction in compaction-prone systems. We propose to address these gaps by 1) conducting a quantitative literature review to synthesize data on the contribution of SOC to increased compaction resistance, and 2) measuring PAW in soil cores that are left intact, are sieved and repacked, or are intentionally compacted in the field and lab. All cores will be collected from a long-term experiment where the addition of organic amendments has significantly increased SOC. This project will provide scientific underpinning for management interventions to address compaction and reduced water-holding capacity to inform both implementation of long-term research trials through the Soil Health Initiative and the adoption of soil health-building practices on commercial farms.