[Characteristics of soil organic carbon and total nitrogen under different land use types in Shanghai].

By the methods of field sampling and laboratory analysis, this paper studied the variations of soil organic carbon (SOC) and total nitrogen (TN) contents and SOC density under different land use types in Shanghai. Significant differences were observed in the test parameters among different land use types. The SOC density was the highest in paddy field (3.86 kg x m(-2)), followed by in upland (3.17 kg x m(-2)), forestland (3.15 kg x m(-2)), abandoned land (2.73 kg x m(-2)), urban lawn (2.65 kg x m(-2)), garden land (2.13 kg x m(-2)), and tidal flat (1.38 kg x m(-2)). The assessment on the effects of three types of land use change on the test parameters showed that the conversion of paddy field into upland resulted in a significant decrease of SOC and TN contents and SOC density; the abandonment of farmland was not an effective way in improving SOC storage in the Yangtze Delta region with abundant water and heat resources, high soil fertility, and high level of field management; while the 4-5 years conversion of paddy field into artificial forestland decreased the SOC and TN contents and SOC density, suggesting that in a short term, the soil carbon sequestration effect of the conversion from paddy field to forestland was at a low level, due to the limitation of vegetation productivity.