Is intensive management associated with low soil carbon in Irish farms? Implications for developing indicators of farm soil health and nature value

Ecologically functioning soils are increasingly viewed as a key component of sustainable agriculture, a means of sequestering carbon and a major contributor to farmland biodiversity. It is generally considered that intensively managed agricultural systems are associated with reduced soil health and require high chemical inputs to maintain soil nutrients. It is important, therefore, to clarify which soil parameters exhibit clear differences between high- and low-intensity farm management and, subsequently, which parameters might then be considered as meaningful indicators of soil health. This study investigated 30 physico-chemical properties of soils collected from 31 Irish farms. Although several soil parameters showed clear differences between the two study areas (Counties Sligo and Wexford), a much smaller subset of properties showed meaningful differences among intensively, intermediately and extensively managed farms. The clearest patterns were shown by several, co-correlated, carbon-based properties, which were all lower in farms under intensive management. The average total carbon content of intensively managed farms was <5%, and we suggest that this might be used as an initial threshold indicator of a degraded and/or low-carbon soil for Irish farms. In general, our study adds additional support for the use of carbon-based parameters as indicators of farm soil health, but further work is needed to ascertain whether different calibrations are required in different regions and for different soil types. In a wider ecological capacity, soil carbon could be included in a suite of environmental and ecological indicators, such as habitat heterogeneity, floral richness and invertebrate diversity, already proposed as measures of farm nature value.