Tillage Systems Influence on Soil Microbial Community Structure.

Agricultural management practices such as tillage and fertilizer application may cause changes in soil microbial community structure. The objective of this study was to examine soil microbial communities under conventional and no-tillage (conservation) practices in a Decatur silt loam soil cropped to corn. The field experiment located in Belle Mina, AL was arranged in a randomized complete block factorial design with four replications and tillage as factor. Soil samples were taken at depths of 0-5 and 5-15 cm in April of 2008. The soil samples were analyzed for soil organic carbon, total nitrogen, and phospholipid fatty acids (PLFA). No-tillage treatment had significantly higher soil organic carbon and total nitrogen when compared to conventional tillage treatment. Soil microbial biomass estimated from total phospholipid fatty acids for no-tillage treatment was 163% greater than conventional tillage treatment at 0-5 cm depth and 27% greater at 5- 15 cm depth, ranging from 72  to 306 µg g^-1. Principal component analysis of phospholipid fatty acid profile shows that soil microbial community structure varied by tillage practices and soil depth. The first three principal components explained 81% of total sample variance. Phospholipid fatty acids 10 methyl 16: 0, 16:1ω7c, 18:1ω9c, 18:1 ω7c, 18: 3 ω6, 9,12c, i17:1, and cy19:0 were most influential for the first three principal component axes. Analysis of variance (ANOVA) on the first principal component shows that tillage, soil depth, and the interaction effect were significant at P=0.001. ANOVA on the third principal component shows that tillage and soil depth were significant at P=0.01. The first principal component separated the soil depth effect and the third principal component separated the tillage effect. These results indicate that changes in soil microbial community structure associated with tillage practices occurred at the surface layer.