Soil properties and C dynamics in abandoned and cultivated farmlands in a semi-arid ecosystem

摘要

Land abandonment might be an alternative management for restoring soil conditions and C from prolonged cultivation and agricultural practices. In the present study, the influence of 18-22 years of land abandonment on soil properties, C dynamics and microbial biomass was evaluated in closely situated wheat and alfalfa farmlands, and abandoned lands on calcareous soils, Central Iran. Soil properties of the 0-15 and 15-30 cm depths from abandoned lands were compared to those from conventionally cultivated lands (i.e., continuous wheat-fallow and alfalfa-wheat rotation) common in calcareous soils of Central Zagros Mountains. Soil bulk density in the 0-15 and 15-30 cm layers decreased significantly while total porosity increased significantly in abandoned lands. Generally, soil aggregate stability tended to increase within the abandoned fields owing to increased water-stable macro-aggregates. Soil organic C (OC) contents (g kg(-1)) and pools (Mg ha(-1)) in the 0-15 cm soil layer increased significantly in abandoned lands compared with cultivated lands, with no effect in the 15-30 cm soil layer after 18-22 years of land abandonment, suggesting the restoration of C is pronounced in the upper 0-15 cm soil depth . The total C accumulation in abandoned lands was 7.0 Mg C ha(-1) for the entire sampling depth (0-30 cm) over the 18-22 years of land abandonment, which was 26% greater relative to cultivated lands. Carbon mineralization (Cmin) followed a trend similar to organic C, whereas C turnover (Cmin/OC ratio) was slightly greater in wheat fields. However, soil microbial biomass C (MBC) did not vary considerably among the three land uses. In brief, improvements, albeit slowly, in soil properties of the top layer with the cessation of cultivation indicated that land abandonment may result in enhanced soil C sequestration, and would maintain fertility and productivity of the farmlands of semi-arid climates.