Time in pasture rotation alters soil microbial community composition and function and increases carbon sequestration...

Soil carbon (C) sequestration plays an important role in mitigating global climate change, and certain land utilization strategies can exert a pronounced effect on carbon storage. Land use practices, such as planting previously cropped lands into perennial grasslands, can increase soil C sequestration; however, the temporal response of soil C pools to such changes in land use are likely complex and not well quantified. In the current study, a space-for-time approach was used to assess the response of soil C sequestration and microbial community composition during a five-year grazed pasture rotation following three years of vegetable production on a central Kentucky farm. After 5 years in pasture, soil organic C and N in the top 15 cm increased 20.6% and 20.1%, respectively, from year 1 levels, and particulate organic matter C (POM C) increased 53.5%. A carbon mineralization (CM) assay indicated that the potential release of CO₂ also increased with time in pasture rotation. When compared to permanent pasture (not previously used for vegetable production), soil microbial community composition differed in rotation years 1-3 but became similar in years 4 and 5. Multi-response permutation procedure (MRPP) analysis showed that CM and POM were key factors affecting microbial community composition. Soil microbial community composition also varied with time of year (season), but to a lesser degree than with pasture duration. Overall, incorporation of perennial pasture into cropping systems can have profound effects on microbial community composition and function, increasing soil organic C, and consequently enhancing the potential for C sequestration; however, whether these increases in C storage persist throughout the full cropping sequence (i.e., once the pasture has been returned to vegetables) and/or how these changes influence subsequent vegetable production remains to be evaluated.