Soil pH Influences on Microbial Functional Responses to Crop Rotational Management and Field Translocation

Structural disturbance of soil such as that caused by tillage or translocation for infrastructure projects can induce changes in soil microbial functions eliciting large fluxes of CO₂. Soil pH, often referred to as a master variable in the context of soil biology, exerts a strong influence on both the structure and function of microbial communities as well as the physical structure of the soil. In order to better understand the interaction of soil pH and large-scale physical disturbances in controlling these fluxes, we took the opportunity presented when moving an entire experimental field to a new location to look at how changing soil structural conditions influenced the activity of the microbial community. Soils under long-term (60 years) pH manipulation were dug from the original experimental site (Woodlands Field, SRUC, Aberdeen) and transported to a new experimental site less than 1 mile away (Aberdeen Cropping Experiment (ACE), Aberdeen), excavated soils were thoroughly mixed before reinstatement. This produced a significant decrease in bulk density and concomitant increase in macroporosity as expected (p = 0.027 and p = 0.021 respectively), with more pronounced changes at lower pH. There were consistent increases in the fraction of water-stable aggregates from the soil translocation, where the field averages of Woodlands and ACE were 91% and 95% respectively (p < 0.001). However, there were no discernible differences across the pH range (p = 0.641), despite greater changes occurring at lower pH treatments. We also observed changes in respiration rates of soils after translocation, rates were slightly increased at low pH, reduced at mid-range pH, and stable at high pH, although none of these were significant changes (p = 0.081). Soil pH was a dominant factor in controlling some aspects of the soil physical properties. Soil pH had variable magnitudes of influence, in particular, more acidic soils were more vulnerable to changes in the physical structure, where the volume of large pore spaces increased dramatically. This could explain the increased CO₂ efflux in acidic soils, however, microbial communities in mid-range pH treatments demonstrated the greatest vulnerability to large-scale physical disturbance, which is likely due to the threshold pH determining their respiration pathway. This research demonstrates that soil management in large-scale disturbance should have altered management, guided by the soil pH.