Soil Microbial and Soil Enzyme Activity in a Discontinued Farmland by the Lower Shiyang River

To better understand the changes in soil conditions after agriculture use ceases,we measured and analyzed the changes in three components-soil microbial quantity,soil microbial biomass,and soil enzyme activity-in sample sites where farming had been discontinued for different periods( 1,2,3,4,5,8,15,24 and 31 years),in the lower Shiyang River area. By using the data,the correlations between the three components were also studied in 2012. The three components,respectively,contained 1) bacteria,fungi,and actinomycetes; 2) microbial biomass carbon,microbialbiomass nitrogen,and microbial biomass phosphorus; and 3) catalase,sucrase,urease,and phosphatase. Synchronic space investigation was adopted instead of diachronic temporal investigation. Results showed that bacteria were the most abundant of the three soil microorganisms in the nine soil samples taken 31 years after farming ceased,followed by actinomycetes and fungi. Overall,the maximum weighted average of the three soil microbial quantities all occurred in the first 8 years after farming ceased. The quantity of soil microbial biomass carbon initially decreased with increasing time since farming ceased. It gradually increased starting in the 4thyear and reached the peak in the 24 thyear,after which it became stable. The soil microbial biomass nitrogen appeared to increase with time. After the maximum weighted average in the 4thyear,there was a steady reduction with large significant differences in soil microbial biomass nitrogen among soil sites of various ages. The weighted average soil microbial biomass phosphorus increased at the same pace as nitrogen at the beginning of the soil restoration period. The biomass phosphorus level climaxed at the 8thyear,after which it tended to decline gradually before finally stabilizing. The general trend of soil enzyme activity decreased,but with fluctuations,with increasing soil succession age. Moreover,soil microbial quantity,soil microbial biomass,and soil enzyme activity declined dramatically in all restoration ages with soil depth from 0 to 10 cm,10 to 20 cm,and 20-30 to 30-40 cm. In addition,the surface soil microbial biomass and soil enzyme activity were the largest among the four soil levels. The changes in soil microbial quantity,soil microbial biomass,and soil enzyme activity were extremely slow. In addition,an interactive process and a feedback response between the three components was observed. Highly significant correlations were found,especially between fu