Influence of nitrogen deposition on soil nitrogen characteristics in the typical steppe on Loess Plateau

To study the influence of nitrogen addition on soil nitrogen characteristics in the steppe on Loess Plateau, six levels of nitrogen (N) treatments, 0, 1.15, 2.3, 4.6, 9.2 and 13.8 gm-2 were conducted in the experiment. Based on the field sampling and laboratory analysis, the responses of soil total nitrogen (TN) and light fraction organic nitrogen (LFON) contents to the N addition were examined. The results showed that the early N addition had no significant effect on the TN content in the 0-40 cm soil layer. However, the early N addition significantly increased LFON content and LFON/TN in the 0-10 cm soil layer. There were no obvious changes of LFON and LFON/TN in the 10-20 cm and 20-40 cm layer among treatments. LFON and LFON/TN were more influenced by the early N addition than TN. Therefore, LFON and LFON/TN were sensitive indictors of soil N dynamics to the early N addition in the steppe on the Loess Plateau.