Mineral associated organic carbon correlates with soil health in agricultural fields

Abstract Increasing terrestrial carbon storage can reduce atmospheric carbon dioxide levels as a climate mitigation strategy. Agricultural soil offers potential for persistent soil carbon sequestration. Mineral-associated organic carbon (MAOC) is generally more persistent than particulate organic carbon (POC), but it is unclear how much influence soil health and management can have on MAOC relative to climate and edaphic conditions. Soil samples from 196 agricultural fields on 77 farms throughout Vermont were fractionated by size to understand how these factors affect the amount and proportions of POC and MAOC. Our results reveal a significant effect of crop type, climate, soil texture, and aggregate stability on these carbon fractions. Hay and pasture fields had on average 69% more POC and 30% more MAOC than corn and vegetable fields. Both POC and MAOC increased with improved soil health scores suggesting that healthier soils store more carbon in both fractions. MAOC dynamics also varied with soil texture. In clay-rich soils, MAOC increases with mean annual temperature (MAT), particularly in regions with higher mean annual precipitation (MAP). However, this effect is the opposite in soils with lower clay content in which MAOC decreases with higher MAT and MAP. Overall, our findings demonstrate that MAOC can be influenced by management, highlighting how effective soil management strategies aimed at increasing soil health like planting perennials can also enhance long-term carbon sequestration in agricultural soils.