Phospholipid fatty acid biomarkers show positive soil microbial community responses to conservation soil management of irrigated crop rotations

The increasing acreages of crops like potato and sugar beet, which return little C to the soil, and whose harvesting methods cause soil disturbance, led to the establishment of a 12-yr study to evaluate soil conservation (CONS) management systems in southern Alberta. The CONS management systems, applied to 3- to 6-yr crop rotations, were compared with conventional (CONV) management systems that included wheat monoculture. The CONS management was a suite of practices that included addition of cattle manure compost, reduced tillage, diverse crop rotations and use of cover crops that CONV management did not have. In the last two years of the study (2010 and 2011), soil microbial biomass was measured in bulk soil and wheat rhizosphere using the substrate-induced respiration method and phospholipid fatty acid (PLFA) biomarkers. beta-glucosidase enzyme activity was measured to evaluate soil functioning (C cycling). Total soil microbial biomass, and that of its components (fungi and bacteria), was significantly greater under CONS management than under CONV management. The total PLFA contents of 3- and 4-yr CONS rotations (15.24-34.69 nmol g(-1) soil) were 84-193% greater than those in CONV management (33.45-63.66 nmol g(-1) soil) when differences were significant, and fungal PLFA was up to 382% greater. beta-glucosidase activity was 50% greater under CONS management than CONV management. Principal component analysis confirmed that the soil microbial community structures in the different rotations were shaped by management practices. These positive responses of soil microbial communities to conservation management will enhance biological processes including nutrient cycling and biological pest control. (C) 2016 Published by Elsevier B.V.