Rice-maize rotation alters soil carbon dynamics in saline-alkaline soils of Ningxia province, northwest China

Abstract

Long-term crop production practices have indicated that rice cultivation and rotation are effective strategies for enhancing soil quality and crop yields in saline-alkaline soils. However, the impacts of long-term rice-maize rotation on soil carbon dynamics remain unclear. To clarify the mechanisms by which soil salinization and alkalization mediate the distribution pattern of soil organic carbon (SOC) and soil inorganic carbon (SIC), the sample sites were reclaimed under same cultivation and management measures. 18 saline-alkaline sampling sites were selected where maize monoculture (M) and rice-maize rotation (RM) have been continuously for about 30 years in Ningxia province, northwest China. Soil samples were collected from both M and RM after the harvest of maize and rice in 2024, respectively. The results showed that there was no significant difference in most salinity properties between M and RM. The average contents of SOC were 9.55 g kg^–1 in topsoil and 6.22 g kg^–1 in subsoil of M, which were significantly (p < 0.001) higher than that of RM. No significant difference was observed in SIC between different land use and soil depth, which was closely associated with pH. And soil depth significantly influenced TC (25.66 g kg⁻¹ in topsoil and 21.88 g kg⁻¹ in subsoil of M, 19.35 g kg⁻¹ in topsoil and 19.71 g kg⁻¹ in subsoil of RM) and SIC/SOC (1.71 in topsoil and 2.61 in subsoil of M, 3.51 in topsoil and 5.14 in subsoil of RM), which led to the difference in soil carbon stocks between M and RM. The dynamics of SOC and SIC in RM were affected by soil texture (silt and sand contents) and minerals (Fe_o and Fe_d c_ontents, Fe_o,/Fe_d), which played a key role in soil carbon sequestration. In brief, the study revealed that long-term rice-maize rotation can alter soil salinization and alkalization, compared with maize monoculture, and strongly govern soil carbon sequestration through organic and inorganic pathways, thereby contributing to the further understanding of agricultural practices in saline-alkaline environments.