The data set comprises biomass values and mineral nutrient values from experimental plots located at Sourhope, Scotland. On five occasions throughout each of the 1999, 2000, 2001 and 2002 growing seasons, grass cuttings were collected from a 50 x 50 cm cell area from each of the four main sub-plots within each of a set of experimental main-plots, and biomass values calculated. In addition, mineral nutrient analysis was carried out for the July 1999 grass cuttings. 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 (Grid reference: NT 8545 1963). During the experiment, the site was monitored to assess changes in above-ground biomass production (productivity), species composition and relative abundance (diversity). The primary aims of the Programme were to achieve simultaneously an understanding of the biological diversity of the soil biota and the functional roles played by soil organisms in key ecological processes. In seeking to achieve these aims, 24 separate research projects were funded to study soil structure, soil processes (such as the carbon and nitrogen cycles) and the roles of micro-fauna and flora (Bacteria, Nematoda, Protozoa and Fungi), microarthropods (including Collembola and Acari), invertebrate root feeders (Tipulid, Bidionid and Scarabeid larvae), meso-fauna (such as Enchytraeidae) and macro-fauna (including Megadrili, Mollusca and Coleoptera). Full details about this dataset can be found at https://doi.org/10.5285/1a278fbf-b8b2-472d-9100-5fb432095f63