Testing for a dual microbial and mineralogical control on the response of soil organic matter to regenerative practices

Abstract:

Agricultural regenerative practices generally increase soil organic matter (SOM), but the variable magnitude of SOM response and our current inability to explain this variability presents several challenges. Land managers face uncertainty in ‘return on investment’ for regenerative practices; rationale for spatial targeting of regenerative practices remains and elusive; and estimates of SOM regeneration potential lack precision. In order to explain variable SOM response to regenerative practices, we investigate two theories about controls on SOM dynamics that have been inadequately tested and integrated. First, soil mineralogical properties other than texture have been recently demonstrated to operate in a pH-dependent context to control SOM stocks. Whether the same pH-dependent controls hold over SOM response to regenerative practices has not been demonstrated. Second, microbial anabolism has received abundant attention as a control on formation of new mineral-associated organic matter (MAOM), despite minimal empirical linkages. We will present data from 16 long-term agricultural research sites in United States agricultural regions spanning a soil pH gradient. Within each site, soils with paired regenerative and conventional management histories will be described for SOM, MAOM, and particulate organic matter (POM) fractions, as well as mineralogy and microbial properties. We will present these preliminary results as a part of a wider project designed to integrate them with the MAOM formation and POM persistence capacities of these soils.