Soil microbial populations, activity, and community structure in continuous corn or forage systems under organic or inorganic fertilization in eastern Canada

Succession of soil microbial communities proceeds interdependently with crop development under the control of edaphic, agricultural, and climatic conditions. Soil microbial community composition and activity were characterized in two managed cropping systems (continuous corn or mixed forage) receiving liquid hog manure (LHM) or inorganic fertilization (IF) since 1989. Microbial community composition was determined from patterns of phospholipid fatty acids (PLFA). Soil microbial biomass C, enzymatic activity, and total phospholipids were greater under forage than under continuous corn. Principal component analysis (PCA) revealed a high degree of variation in PLFA composition and microbial community structure due to treatments and time of sampling. The first two PCA axes explained 80 to 90% of the variability on all sampling dates. Two main groups were created along the first component, the first comprising all forage treatments and a second with LHM-treated continuous corn. The IF and control-treated continuous corn were differentiated from all others on the second component. All groups were characterized by specific microbial communities. The most significant shift in specific groups of fatty acids was caused by LHM addition to continuous corn, especially due to the relative abundance of the fungal fatty acid 18:2(9,12). Our findings indicated that the addition of organic materials, rich in available C and N, induced development of diverse microbial populations, which can be successfully monitored by phospholipid fatty acid profiles.