The accumulation of mineral nitrogen in soil during drying events is affected by soil management

Soil drying events play a critical role in shaping nitrogen (N) cycling in drylands by influencing N availability and the risk of N losses. This study examines how different soil management practices (no-tillage (NT) and traditional tillage (TT), with and without liming)affect N mineralization and the accumulation of inorganic N during drying periods in a hot-summer Mediterranean climate. Using soils from a long-term field experiment in southwestern Spain, we evaluated changes in inorganic N, enzymatic activities, and the abundance of genes related to N cycling during a summer fallow under field conditions, and in a complementary laboratory incubation under controlled temperature conditions. Field results showed a significant accumulation of inorganic N (from 6.47 to 11.43 mg N kg⁻¹) during drying, with a synergistic effect of NT and liming. Enzymatic activities (β-glucosaminidase, leucine aminopeptidase, proteases) and gene abundances (chiA, pepA, apr) declined with drying but remained higher under NT than TT. The laboratory study confirmed that management-induced differences in N cycling were mainly due to changes in soil biogeochemical properties (organic matter, pH), rather than changes in microclimatic conditions (soil temperature and moisture). While NT and liming enhanced N mineralization and microbial resilience, they also promoted inorganic N accumulation, increasing the potential for N losses (e.g., via N₂O emissions) upon rewetting. These results highlight the importance of integrating adaptive practices, such as summer cover cropping, into conservation agriculture to reduce N losses and improve nutrient use efficiency under increasingly frequent drought conditions.