Mineral‐associated organic matter and soil health indicators in subsiding cultivated histosols of the Everglades Agricultural Area

Abstract Soil drainage leads to subsidence in organic‐rich peat soils (histosols) due to compaction and accelerated soil oxidation, removing carbon (C). Research suggests mineral‐associated organic matter (MAOM) promotes soil C persistence, but the prevalence of MAOM in cultivated histosols and its relationship with commonly measured soil health indicators (SHIs) are unknown. The objectives of this study were to (1) quantify soil C fractions and diverse SHIs in the Everglades Agricultural Area, Florida, to comprehensively evaluate the soil condition, and (2) determine if any existing SHIs, general soil properties, depth, or profile thickness may predict MAOM abundance. Soil cores were collected at 15 locations and up to 45‐cm depth. Profile thickness (a proxy for oxidation) was determined by probing to bedrock, and C fractionation included both physical and density separation. Soil organic matter (SOM) content averaged 62% by mass, with nearly 50% of the soil aggregates >2 mm. Potassium‐permanganate oxidizable C averaged 28.2 ± 0.9 g kg − 1 , and organic C concentration was five times greater than inorganic C. Particulate organic matter‐Carbon (POM‐C) accounted for >99% of soil (220.6 ± 9.3 g kg − 1 ), while mineral‐associated organic matter‐Carbon (MAOM‐C) represented <1% (0.3 ± 0.1 g kg − 1 ). POM‐C was predicted by soil profile thickness and several SHIs, but MAOM‐C was not well predicted by almost any parameter measured. Results emphasize the predominance of unassociated organic C and suggest MAOM may serve as a unique SHI for organic soils. Management practices should focus on preventing further loss of vulnerable POM‐C and promoting MAOM‐C formation.