Spatiotemporal variations in soil CO2 fluxes under a winter wheat-summer maize cropping system in the North China Plain

Abstract

Most studies on soil CO2 fluxes focus on the upper soil layers (i.e., 0–200 mm); however, there is a lack of investigation into soil layers below 200 mm, even though about half of soil organic carbon (SOC) is stored at these depths. In order to investigate the responses of CO2 fluxes in subsurface soils to crop residue incorporation in the topsoil, a field experiment comprising two treatments (i.e., conventional tillage with and without crop residue incorporation) was carried out under a winter wheat-summer maize cropping system from 2014 to 2016 in the Yucheng Agricultural Station, Shandong Province, China. The results showed that soil CO2 fluxes had large spatiotemporal variabilities and were significantly affected by crop residue applications (P < 0.05). Soil CO2 fluxes increased with soil depth. The CO2 fluxes from 100 to 400 mm soil depths were 1.1–5.1 times higher than those from 0 to 100 mm soil depths. Incorporation of crop residues into the soil significantly increased soil CO2 fluxes in all sampled layers (P < 0.05), and the magnitude increased with increasing soil depth. Soil moisture and the ratio of soil dissolved organic carbon to nitrogen (DOC/DON) were the dominant factors regulating soil CO2 fluxes in the wheat growing season, whereas soil DON concentrations dominated in the maize growing season. Our study indicated that deep soil C was more vulnerable to the incorporation of crop residues than the C present in surface soil. Incorporation of crop residues into surface soil might not increase SOC sequestration in the subsurface soil.