Data for the manuscript 'Smart mixture design can steer the fate of root derived carbon into mineral-associated and particulate organic matter in intensively managed grasslands'

To determine the fate of root-derived carbon (C) input from grassland mixtures into distinct soil organic carbon pools — particulate organic matter (POC) and mineral-associated organic carbon (MAOC) — a field trial was established, comparing pure stands of perennial ryegrass under high and low nitrogen (N) fertilizer application rates with grassland mixtures containing legumes and forbs at increasing levels of species richness. The mixtures received the low N application rate. Through multiple-pulse ¹³C-CO₂ labeling during the first growing season (2022), we captured the net formation of MAOC and POC. At the end of the growing season, soil cores with a diameter of 30 cm were excavated to a depth of 25 cm (topsoil) and transferred to the lab. We removed roots from the soil and performed particle-size fractionation to trace fresh organic carbon (net rhizodeposited C) into particulate organic matter (POM) and mineral-associated organic matter (MAOM). Using a cut-off of 50 μm, particles larger than 50 μm were classified as POM, while those smaller than 50 μm were classified as MAOM. We related these soil C fractions to five morphological root traits, as well as to the lignocellulose index and the C:N ratio in root biomass.