Dynamics of soil nitrogen along a topoclimatic gradient in the Judean desert

Nitrogen is considered to be one of the major deficient nutrient elements in desert soils, where levels of nitrogen and its fractions undergo rapid tempospatial and chemical changes with the changes in season, according to water availability. A better understanding of this knowledge would be useful for describing the nitrogen state and changes in arid to semiarid systems. The present study investigated mineral nitrogen content in soils sampled from four sites in the Judean Desert along a topoclimatic gradient ranging from Mediterranean to arid conditions, over a period of two years. It was concluded that, along the Judean Desert topoclimatic gradient, temporal dynamics in total soluble nitrogen (TSN) (0.4-80.0 mg kg^-1 dry soil), mainly consisting of NH₄⁺-N (0.03-28.1 mg kg^-1 dry soil) and NO₃^--N (0-57.2 mg kg^-1 dry soil), are closely related to the soil moisture pattern. However, the effect of soil moisture on long-term TSN spatial dynamics is not so pronounced, due to leaching and denitrification. Significantly higher NH₄⁺-N than NO₃^--N levels exist in soils during dry periods, whereas an opposite pattern was observed during the wet seasons. Ammonia may be volatilized, preventing ammonium from accumulating with a decrease in soil clay content. More NO₂^--N accumulated in a drier site than in moister sites, probably due to aridity having a different impact on different nitrification processes.