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Human demand for food and energy has led to significant changes in the level of reactive nitrogen (Nr) released to the atmosphere and then deposited in the biosphere. This study aimed to investigate artificial N deposition's impact on the forest floor and soil chemical properties in an oak (Quercus castaneifolia C. A. Mey) plantation in the north of Iran. Twelve plots of 200 m2 (20 m × 10 m) were set up in the study area. Four N treatments were considered: zero (control), 50 (low), 100 (medium), and 150 (high) kg N ha−1 year−1. The total N, P, K, and organic C (OC) of the forest floor were measured. Soil N, available P, available K, pH, EC (Electrical Conductivity), OC, microbial biomass C (MBC), and urease enzyme activity were measured in the 0-10 cm depth. The concentration of total N and P of the forest floor was significantly higher in the high N treatment. The total concentration of N (+36%), the urease activity (+44%), and EC (+12%) of soil increased with raising the high-N treatment compared to the control, but the MBC (-20%), available P (-28%), and available K (-15%) were significantly reduced in the high-N nitrogen treatment.

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