Effects of the Gully Land Consolidation Project on soil properties and carbon stocks of farmland in the Chinese Loess Plateau

A megaproject named Gully Land Consolidation (GLC) was implemented in the Chinese Loess Plateau (CLP) to address food shortages. However, its effects on soil properties and carbon stocks remain unclear. This study evaluates the effects of the GLC project on soil properties and carbon stocks by analyzing the properties of 14 farmland soil profiles (0-500 cm depth) in the Gutun watershed (GT-T), a typical area treated by the GLC project. Soil particle size, water content (SWC), bulk density (BD), contents of soil organic carbon (SOC), inorganic carbon (SIC), and total carbon (TC) were measured, and carbon stocks were calculated. Data from the GT-T watershed were compared to untreated areas in the CLP (CLP-U) and outside the CLP (Other-U). The results showed that the silt proportion (76.0%), SWC (17.7 ± 5.2%), and BD (1.5 ± 0.2 g cm^-3) in the 0-500 cm depth in the GT-T watershed was 1.1 to 2.1 times, 1.6 to 2.8 times, and 1.0 to 1.3 times higher than in untreated areas, respectively. However, the SOC stock (2.5 kg m^-2) at 0-100 cm depth was 0.7 to 10.2 kg m^-2 lower than in the untreated areas. These results indicate that although the GLC project can improve soil structure and water retention capacity, it may also lead to the loss of surface SOC, thereby reducing soil fertility. The protection and replenishment of surface SOC should be emphasized during the cultivation and management of the newly reclaimed farmland in GLC-treated areas. This study highlights the effects of the GLC project on soil properties and carbon stocks and provides valuable insights for optimizing land reclamation management in the CLP.