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

Rahman, M.T., Liu, S., Guo, Z.C., Zhang, Z.B., Peng, X.H.
Soil & tillage research 2019 v.189 pp. 110-122
Miscanthus, aggregate stability, carbon, corn straw, microaggregates, nitrogen, oxides, soil respiration, stable isotopes, tracer techniques
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 13C 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 (δ13C = −23.2‰). Soil respiration, aggregate stability (MWD), REO concentrations and 13C 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 < 0.001). As a result, the aggregate turnover of the soil incorporated with maize straw was faster than that of the soil incorporated with miscanthus straw. The N input increased the aggregate turnover of the soil incorporated with miscanthus straw but this effect was minimal for the maize straw amended soil. The new C accumulated more, but decomposed faster in macroaggregates than in microaggregates. A significant positive relationship was observed between the 13C concentration and the aggregate turnover rate (P < 0.01) in sole straw amended treatments, whereas this relationship became weak after N input. Our results demonstrate that aggregate turnover depends on the residue quality and N input when the residue decomposition is under N-limited conditions.