Crop rotational diversity alters the composition of stabilized soil organic matter compounds in soil physical fractions

Abstract Crop rotational diversity is an important part of sustainable agricultural and soil management to improve crop yield and soil fertility including enhancing soil organic matter (SOM) stabilization. Because of the physical protection via interactions with soil minerals, SOM in mineral-associated fractions is believed to be longer-lived and more stable relative to SOM in particulate (light) fractions. However, it is still unclear how crop rotational diversity alters soil carbon distribution, composition and stabilization in soil physical fractions. To address this, we studied a 37 years’ agricultural site with different crop rotational diversity (from continuous corn or alfalfa up to four species (corn, soybean, winter wheat, and red clover)). Soil carbon analysis, targeted compound analysis and nuclear magnetic resonance spectroscopy methods were used to obtain the distribution and degradation of SOM components in light and mineral-associated (F53–2000 µm, F2–53 µm, and F<2 µm) fractions. Higher soil organic carbon (SOC) concentrations were observed in F<2 µm with relatively high diversified crop rotations (three and four types of crops) compared to monoculture or two crops in the rotations, which suggests that carbon storage is enhanced in mineral-stabilized pools. Higher concentrations of long-chain aliphatic compounds as well as increased accumulation and preservation of lignin-derived compounds in fine aggregates (<53 µm) were also observed with relatively high diversified crop rotations. Overall, the increased concentration and preservation of specific SOM compounds as well as increased SOC in finer mineral-associated fractions (<53 µm) suggests that crop rotational diversity may enhance the long-term stability of SOM in agroecosystems.