Land abandonment effect on N mineralization and microbial biomass N in a semi-arid calcareous soil from Iran

Modifications in vegetation cover and soil properties as a consequence of the abandonment of the agricultural activities may influence soil N contents and dynamics. The aim of this study was to investigate the influence of land abandonment on N levels and dynamics in farmlands and abandoned lands in Central Iran. Total N (TN), net N mineralization and microbial biomass N of the 0–15 and 15–30 cm depths from lands abandoned for 18–22 years were compared to those from traditionally cultivated wheat-follow (>45 yr) and continuous alfalfa (>40 yr) fields. Soil TN contents (g kg−1) and pools (Mg ha−1) in the 0–15 cm soil layer increased significantly in abandoned lands, with no effect in the 15–30 cm soil layer after land abandonment. Soil net N mineralization (Nmin) was higher in abandoned and alfalfa fields than in wheat fields, while relative N mineralization (Nmin/TN ratio) was greater in alfalfa fields than in abandoned and wheat fields. However, soil microbial biomass N (MBN) was similar among the studied fields, while MBN/TN ratio in wheat fields was higher than that in abandoned fields. Agricultural abandonment may result in enhanced soil N mineralization and, would maintain long-term fertility and productivity of the farmlands of semi-arid climates.

► The influence of land abandonment on N storage and dynamics in farmlands and abandoned lands was evaluated.
► Soil total N (TN) contents (g kg−1) and pools (Mg ha−1) in the top soil layer increased in abandoned lands.
► The rate of N accumulation in abandoned lands was averaged 2.05 g N m−2 y−1 over 18–22 years.
► N mineralization was high in abandoned and alfalfa fields, while relative N mineralization was high in alfalfa fields.
► Soil microbial biomass N (MBN) was similar, while MBN/TN ratio was higher in wheat than in abandoned fields.