Long-term plastic film mulching and fertilization treatments changed the annual distribution of residual maize straw C in soil aggregates under field conditions: characterization by 13C tracing

Abstract

Plastic film mulching and fertilization strongly affect soil aggregation and dynamics of the total soil organic carbon (C) pool. However, there is limited information on how these agricultural management practices influence the fate and seasonal dynamics of crop residue-derived C in soil aggregates. Therefore, a better understanding of the fate of C derived from crop residues and their location in soil aggregates is crucial to improve our prediction of C sequestration and stabilization in soil. In this study, an in situ 13C-tracing technique was used to identify the dynamic distribution and accumulation patterns of crop residue-derived C in soil aggregates as affected by long-term plastic film mulching and four fertilization treatments (control, CK; nitrogen, N2; organic manure, M2; nitrogen and organic manure, M1N1). The fate of 13C-labeled maize straw in loam soil was studied over 360 days using in situ incubation of 0.2% equivalent dry straw incorporated into the soil and aggregate size fractionation. Soil samples were separated into four particle-size fractions [large (>2 mm) and small (1–2 mm) macroaggregates; large (0.25–1 mm) and small ( M1 N1 > N2 > CK. Both the content of straw-derived 13C in aggregate fractions and the proportion of 13C in total soil samples decreased considerably from the microaggregate fractions and increased moderately in the macroaggregate fractions in a manner enhanced by plastic film mulching and by seasonal transitions, specifically from spring (day 0) to summer (day 60). In addition, the decomposition of maize straw and soil aggregation exhibited a direct correlation in which the content of 13C-SOC and mean weight diameters decreased over the course of the 360-day experiment. Our results suggest that certain amounts of straw-derived 13C could accumulate in microaggregates, which play an important role in long-term C sequestration, while a large part of straw-derived C tends to transfer from microaggregates to macroaggregates over time as affected by long-term plastic film mulching coupled with fertilization. This study improves our understanding of the effect of plastic film mulching and different fertilization regimes on the retention and stabilization processes of straw-derived C in soil.