[Distribution characteristics of soil nitrogen and its influence factors in different typical zonal soils.]

On the basis of field soil sampling, this paper investigated the distribution characteristics of soil different nitrogen (N) forms and its influence factors in the different typical zonal soils. The results showed that the concentrations of soil extractable total N, extractable organic N and adsorbed amino acids extracted with 0.5 mol·L^-1 K₂SO₄ significantly increased along the altitudinal gradient in the different vertical soils, and their mean concentrations were greater than that in the horizontal soils. The concentrations of soil different N forms widely varied with the soil type in the different horizontal soils. On average, the concentration of soil adsorbed amino acids was approximately 5-fold greater than that of the free amino acids, representing 21.1% of soil extractable organic N. It indicated that the soil adsorbed amino acids extracted with the strong salt solution could serve as an important form of soil organic N. Pearson correlation analysis showed that extractable total N, extractable organic N, ammonium and amino acids in vertical soils were positively correlated with soil organic matter and total N (r=0.57-0.93, P<0.05), but negatively correlated with soil pH and nitrate (r=-0.37--0.91, P<0.05). In the horizontal soils, soil extractable total N, nitrate, organic matter, total N, alkali-hydrolyzable N and cation ions (e.g. K⁺, Ca²⁺, Mg²⁺) were all positively correlated with soil pH (r=0.36-0.85, P<0.05), whereas negatively correlated with soil ammonium and amino acids (r=-0.39--0.81, P<0.05).