Objective To explore the nitrogen release and conservation capacity of forest soil under different cutting methods, and reveal the impact of cutting methods on forest soil N nutrient cycle.

Method A laboratory incubation experiment was conducted to study the effects of selective cutting and clear cutting on gross and net N transformation rates in broad-leaved mixed forest soil in cold temperate zone, using ¹⁵N paired isotope labeling technique and FLUAZ numeric model.

Result In the reserved belt without any cutting, soil gross N mineralization, net N mineralization, gross N immobilization, gross nitrification, and net nitrification rates were 4.16, 1.86, 2.32, 0.368, and 0.343 mg∙kg⁻¹∙d⁻¹, respectively. In comparison with the treatment of reserved belt, soil gross N mineralization rates of the selective cutting and clear cutting treatments significantly decreased by 32.2% and 61.8%, respectively, soil net N mineralization rates significantly decreased by 43.1% and 61.5%, respectively, and soil gross N immobilization rates significantly decreased by 23.3% and 63.4%. Selective cutting had no significant effects on gross and net nitrification rates in soil, while clear cutting significantly decreased soil gross and net nitrification rates by 23.6% and 33.3%, respectively. The correlation analysis indicated that soil organic C and water soluble organic C were the main factors influencing gross and net N mineralization and immobilization rates in soil, and pH was the main factor influencing gross and net nitrification rates in soil.

Conclusion Our results indicate that the decrease of gross ammonium immobilization rate is greater than that of gross nitrification rate after clear cutting, leading to the significant increase of ratio of gn/ia and NO₃⁻/NH₄⁺ in soil, which increases the risk of NO₃⁻ leaching. However, the ratio of gn/ia and NO₃⁻/NH₄⁺ in soil under selective cutting is not significantly different from that of the reserved belt, which is a desirable way of forest harvesting.