Short-term land use conversions influence the profile distribution of soil salinity and sodicity in northeastern China

Soil salinity and sodicity are important factors leading to soil degradation. Understanding the changes in soil salinity and sodicity is important to maintain soil quality and health and for sustainable land use. The main objective of this study was to investigate the short-term influences of land uses on soil salinity and sodicity in northeastern China. The eight dominant soil soluble ions (sodium, potassium, calcium, magnesium, carbonate, bicarbonate, chloride and sulfate), pH, electrical conductivity (EC), total soluble salt content and sodium adsorption ratio (SAR) were determined at 0-50 cm depth under five land uses consisting of corn (Zea mays L.) cropland (Corn), alfalfa (Medicago sativa L.) forage land (Alfalfa), Leymus chinensis (Trin.) Tzvelev grassland (AG), Leymus chinensis (Trin.) Tzvelev grassland for mowing (AG + M) and restored grassland (RG). The results showed that sodium was the predominant cation in Songnen grassland, while the contents of carbonate, bicarbonate, chloride and sulfate had slight differences in the 0-50 cm depth. Compared with soil salinity, soil sodicity was a more serious problem due to the higher soil pH and SAR. EC and SAR were more sensitive to land use conversions due to the higher discrimination ability and value ranges by different land use treatments. Under AG + M, AG and RG treatment, soil EC (20.59%, 23.03% and 19.61%, respectively) and SAR (42.46%, 39.66% and 37.62%, respectively) were lower in the 0-10 cm depth, while soil EC (36.03%, 25.75% and 17.40%, respectively) and SAR (30.86%, 20.18% and 23.09%, respectively) in the 10-50 cm depth were higher than those under Corn. Soil EC and SAR under Alfalfa in the 0-50 cm depth were 4.69% and 1.97% lower than that under Corn, demonstrating that alfalfa planting was better than other land uses to improve soil salinity and sodicity in northeastern China. These results suggested that soil sodicity was a very serious problem in the Songnen grassland, and soil salinity and sodicity can be expected to gradually decrease with the conversion of cropland to grasslands in semi-arid agroecosystems.