Data collected include: plant (shoot and root) biomass, a range of soil conditions including mycorrhizal abundance, microbial biomass carbon & nitrogen, soil extractable ammonia, soil extractable nitrate, soil extractable phosphate, total nitrogen content of soil and the presence of selected mite and collembolan species, and measurements associated with stable isotopes (ratio of isotopes of nitrogen in soil, roots and shoots, total carbon content of roots and shoots, ratio of isotopes of carbon in roots, total nitrogen content of fumigated and non-fumigated acid traps, ratio of isotopes of nitrogen in fumigated and non-fumigated acid traps). These data were collected from a laboratory-based study that examined a range of soil properties to investigate the relationship between microarthropods and soil microbial properties and the short-term partitioning of a dual-labelled organic nitrogen source (glycine-2-13C-15N) between a grassland plant, Agrostis capillaris, and the soil microbial biomass, to determine how soil fauna and their diversity influence plant-microbial competition for organic N. The experiment was carried out at Lancaster University using soil from the NERC Soil Biodiversity site in Scotland. The work was part of the NERC Soil Biodiversity Thematic Programme, which was established in 1999 and was centred upon the intensive study of a large field experiment located at the Macaulay Land Use Research Institute (now the James Hutton Institute) farm at Sourhope in the Scottish Borders. During the programme, the site was monitored to assess changes in above-ground biomass production (productivity), species composition and relative abundance (diversity). Full details about this dataset can be found at https://doi.org/10.5285/e3c79781-09af-4c4f-b6ad-b0bc323e203f