Study on the dynamics of nitrogen and organic carbon in soil of cultivated grassland in Tibet

Surface soil of arable land in different reclamation duration in Qiongjie and Jiangzi of Tibet was sampled to study the dynamics of nitrogen and organic carbon. The results showed that the total nitrogen and soil organic carbon (SOC) content of the topsoil of the farmland decreased within the first two years and then increased in the following years, which presented roughly a Vshaped trend. Generally the ammonium nitrogen (NH4+N) showed same trend, but the nitrate nitrogen (NO3- N) had no significant variation with increasing of arable years. Ammonium nitrogen, total nitrogen and SOC in the surface soil of both regions showed a significant positive correlation (P0.01), but no significant correlation (P0.05) between nitrate nitrogen and SOC.