The data consist of soil carbon in kilogrammes (kg) of carbon per metre squared. Soil cores were taken to a depth of 1 metre and divided into 15 cm depth increments. Soil carbon (kg carbon per metre squared) was determined for all soil depth increments. The soil samples were taken in the Conwy catchment in North West Wales. Samples were collected in the spring of 2014 across a land use intensification gradient ranging from semi-natural peatlands, acid grasslands to improved grasslands and arable fields. Soil parameters were tested across a land use intensification gradient to detect parameters that can predict aboveground biomass production across different land management types. Data were used to enhance the predictions of biomass production in the Joint UK Land Environment Simulator model (JULES). Measurements informed the improvement of the nitrogen cycle component in the model. This dataset is part of a data series where plant and soil measurements were collected together to increase our understanding of coupled aboveground and belowground processes. Measurements were undertaken by trained members of staff from Bangor University, the Centre for Ecology & Hydrology and Exeter University. This data was collected for the NERC project 'The Multi-Scale Response of Water quality, Biodiversity and Carbon Sequestration to Coupled Macronutrient Cycling from Source to Sea' (NE/J011991/1). The project is also referred to as Turf2Surf. Full details about this dataset can be found at https://doi.org/10.5285/dd6835bf-9c7e-4ad6-95f2-d15f24162fb3