Impacts of residue quality and N input on aggregate turnover using the combined 13C natural abundance and rare earth oxides as tracers

Abstract The effects of residue quality and nitrogen (N) input on soil aggregate turnover are not clarified. In this study, aggregation pathways and C cycling were tracked by using rare earth oxides (REOs) and 13 C natural abundance as tracers, respectively. Two residues (maize straw, C/N = 32; miscanthus straw, C/N = 220) coupled with or without N application (200 kg N ha −1 ) were incorporated into the REO labelled soil (δ 13 C = −23.2‰). Soil respiration, aggregate stability (MWD), REO concentrations and 13 C were measured after 0, 7, 14 and 28 days of incubation. The maize straw incorporation resulted in a greater soil respiration and MWD as compared with the poor residue quality miscanthus straw. The N addition improved the miscanthus straw decomposition and MWD, whereas this effect was negligible for the maize straw treatments. The change in the MWD was related to the soil respiration ( P 13 C concentration and the aggregate turnover rate ( P