Soil Chemical Properties and Biological Characteristics of Discontinued Farmland in the Downstream of Shiyang River

Soil inorganic nitrogen (nitrate nitrogen, ammonium nitrogen), enzyme activities (catalase, urease, phosphatase and invertase) and microbial biomass of secondary grassland in an abandoned farmland with different restoration years of Shiyang River are measured and analyzed. The results indicated that the soil ammonium nitrogen decreased and nitrate nitrogen increased in each layer (0-10cm, 10-20cm, 20-30cm, 30-40cm) as the restoration age increased. In addition to the 30-40cm soil layer, soil microbial biomass carbon in each layer had a downward trend in shorter abandoned ages (from 1a to 5a ) and an upward trend in longer ages (from 8a to 31a); soil microbial biomass nitrogen reduced initially (from 1a to 4a), afterward increased (from 4a to 8a) and reached a steady level finally (from 8a to 31a); soil microbial biomass phosphorus increased firstly (from 1a to 5a) and then declined (from 5a to 31a). The activity of catalase altered insignificantly while those of other three soil enzymes varied significantly in the same layer within different restoration years. Soil enzyme activity declined with the increase in soil depth during the same restoration year.