Soil Microbial Community Response to Crop Residue Placement.

Aboveground plant residues provide important substrate for microbial decomposers in agricultural soils. The balance between input and decomposition of crop residues greatly influences turnover and storage of C and placement of crop residues affects decomposition rates and alters the pathway of C through soil food webs. Understanding how residue placement influences microbial abundance and community structure will aid in the understanding of long term fate of residue-derived C. In October 2007, barley residues were either surface applied or mixed (0- to 9-cm depth) into soil microcosms at two sites with diverse conditions, Lethbridge, AB and Ottawa, ON. Microcosms were destructively sampled the following spring and fall and microbial community dynamics were assessed using phospholipid fatty acid analysis (PLFA). Soil microbial community structure differed between sampling dates and soil depths (0-5 cm vs. 5-10 cm) at both locations and persisted for at least one year after treatment application. The findings demonstrate that residue placement affected microbial abundance and community structure, but that specific effects varied with environmental conditions. Given the legacy of a single residue application treatment on microbial dynamics observed here, it is expected that practices affecting long-term residue distribution may ultimately modify microbial processing and fate of residue-derived C in soil.