Simulation of Nitrogen Deposition (Nitrogen Addition Experiments) Impact on Soil Properties in Pine Radiata Stands

Human demand for food and energy has led to major changes in the level of active nitrogen (N) released to the atmosphere. N addition experiments are a reliable way for investigating the effect of extra N deposition on target ecosystems. The present study was carried out to investigate in the effects of an artificial N deposition on the soil biochemical properties of a 20-year-old oak (Pinus radiata) plantation in Hyrcanian forests in the north of Iran. Twelve plots of (20 m × 10 m) were established in the study area. Four N treatments were considered: zero (control), 50 (low), 100 (medium) and 150 (high) kg N ha−1 year−1. N in the form of NH4NO3 solution was manually sprayed onto the plots monthly for one year. Analysis of variance showed that soil characteristics at nitrogen treatment and different seasons and interaction of season and treatment had significant differences (P value <0.01). In this regard and at the end of the simulation period, the lowest soil pH was observed in high treatment (6±0.3) and highest in control treatment (6.8±0.3). The highest amount of total nitrogen was observed at high N treatment (0.55±0.02). But in relation to K and P concentrations, the control treatment (368±2.7) (12±1.6) had highest and high N treatment (266±3) (6.6±0.7) had lowest concentration of P and K, respectively. In this study, due to the increase in nitrate content obtained by adding ammonium nitrate in the nitrogen simulation process, nitrate becomes saturated in the soil and mobile in the soil, and then leaching with base cations and decreasing soil pH.