Contents And Changes Of Soluble Organic Nitrogen In The Different Soils

The soluble organic nitrogen in soil (SON) is defined as the organic nitrogen in soil that could be extracted by water or other salt solutions. The behavior of SON in soil is different from that of mineral nitrogen and insoluble organic nitrogen. The SON is the potential source of dissolved organic nitrogen (DON), and DON is considered as the main N forms losing from forest ecosystems. SON is also one of the labile forms of N available to microorganisms and plants. Therefore, SON plays a vital role in N cycling in forest ecosystems. Recently, researchers found that the content of SON in arable soils in England was as high as mineral N in the soils, and considered it as an important N pool in N cycles. However, more attention has often been focused on the behavior of mineral nitrogen in agricultural soils and overlooked the roles of SON in soil nitrogen cycles; and little is known about the content and characteristics of SON in the soils on the Loess Plateau in China.In this study, persulphate oxidation method was used to determine SON content in different soils. The incubation and field experiments were carried out to study the concentration of SON in soils on the Loess Plateau, and the effects of cultivating types, fertilizer, soil types, and vegetation on SON were also evaluated. The main results showed as follows:1. Effects of the potassium persulfate products from two different companies, oxidizing methods (boiled water and autoclave) and the types of pure water used in the experiment on the accuracy of total nitrogen in solution determined by persulfate oxidation method were studied. The results showed that there were significantly differences in absorbance (at 220 nm and 275 nm) after autoclaving between the different potassium persulfate products produced by different companies; the blank absorbance of a product was as high as 2.5, and had a significant effect on the determination of the method. The types of water, i.e., distilled water or deionized water, had no significant effects on the N recovery of urea. Autoclaving oxidation method (30 min at 120℃) was considered as the optimum oxidizing method, which had a lower blank absorbance, and the urea-nitrogen and ammonium-nitrogen could be recovered completely. When the volume ratio of oxidizing reagent (0.15 mol/LNaOH and 30 g/LK₂S₂O₈) to sample was 1:1, the maximum oxidation concentration of urea-nitrogen was...