An assessment of the soil microbial status after 17 years of tillage and mineral P fertilization management

Agricultural practices, such as tillage and fertilization, are greatly involved in sustainable agricultural soils and their impacts on microbial community and activity must be fully clarified to better understand their roles in soil phosphorus (P) cycling. We assessed the effects of 17 years of different tillage systems and P fertilization on the development of soil microbial biomass, activity, and community structure. The study site was a long-term maize-soybean rotation experiment established since 1992 in eastern Canada. Soil samples were collected at two depths (0-15cm and 15-30cm) in the fall of 2009 from soybean plots under moldboard plow (MP) and no till (NT) management and fertilized with 0, 17.5, and 35kgPha-1. Soil microbial biomass carbon (SMB-C), nitrogen (SMB-N) and P (SMB-P), two microbial activities (dehydrogenase and alkaline phosphatase), and the microbial community structure based on phospholipid fatty acid profiles (PLFA) were determined. Results show all soil microbial variables were greater at 0-15cm than at 15-30cm under NT but not under MP. In the MP treatment, both enzymes activity and fungal biomass were significantly higher than NT at 15-30cm. Principal component analysis of PLFA profiles shows that the structure of the microbial community was first separated by tillage, then by depth, and P fertilization had no significant effect. However, P fertilization significantly influenced SMB-C and SMB-P under NT. Greater SMB-P content was observed with the highest P fertilization applied at 0-15cm, while opposite result were observed in SMB-P and SMB-C at 15-30cm. We conclude that size, activity, and structure of the soil microbial community differed more because of tillage than P fertilization. © 2012.