The Influence of Land Use Change on Chemical and Biological Properties of Steppe Soils in Northern China

This study was conducted in an agro-pastoral transitional zone near Inner Mongolia, northern China, to assess the influence of land use conversion from native steppe to intensive agriculture and from intensive agriculture to alfalfa on soil chemical and biological properties. At two separate sites, plots representing intensive agriculture, alfalfa, and the respective native steppe type (i.e., meadow steppe and typical steppe), were established in 1980. Intensive agriculture lands were cultivated and alfalfa was sown in these intensive agriculture soils since 2002. A sensitivity index, calculated for each measured property by dividing values for the native steppes by corresponding values in intensive agriculture lands or alfalfa lands, was also used to evaluate the responses of the soil quality to land use conversion. The amount of root biomass in intensive agriculture soils was 88% at a 0-10cm depth and 76% at a 10-20cm depth lower than those in native steppe soils at both sites. Concentrations of soil organic carbon (C), total nitrogen (N), total phosphorus (P), organic P, and activities of urease, dehydrogenase, acid and alkaline phosphatase at 0-10cm depth in both steppe types all significantly decreased after native steppes were converted to intensive agricultural lands. Planting alfalfa in intensive agriculture soils increased root biomass and reduced soil pH. Alfalfa improved soil organic C and total N at the meadow steppe site, but not at the typical steppe site, indicating that the directions steppe systems might take after the native steppe was cultivated depended on initial soil properties of the steppes rather than on the disturbance itself. Sensitivity analysis indicated that dehydrogenase activity, spore density of arbuscular mycorrhizal fungi, and total N were more sensitive to land use conversions than total organic C and other enzyme activities.