Effects of Tillage Practices on Soil Organo-Mineral Complexes and Organic Carbon Distribution Under Continuous Maize Cropping in the Black Soil Region of Northeast China

Organo-mineral complexes are intimately involved in protecting the stability of soil organic carbon (SOC), as they are influenced by environmental factors such as pH and redox conditions, as well as by the implementation of appropriate management practices. Nevertheless, the influencing factors of organo-mineral complexes, as well as their response to tillage practices, remain poorly understood. This study investigated the effects of rotary tillage (RT), plow tillage (PT), and no tillage (NT) on organo-mineral complexes (water-dispersible G0 fraction, sodium-dispersible G1 fraction, grinding-dispersible G2 fraction) and their organic carbon (OC) in the black soil region of Northeast China in 2002 and 2022. Compared to 2002, the content of organo-mineral complexes and their OC in 2022 increased by 5.54% and 3.15%, respectively. Relative to RT, PT and NT increased the organo-mineral complex content by −0.39% and 7.98% and increased the OC content by −8.60% and 10.19%, respectively. Between 2002 and 2022, tillage measures led to greater contributions (78.71%) of organo-mineral complexes to soil carbon sequestration. In 2022, the NT treatment showed significantly higher exchangeable Ca²⁺ content than both the RT and PT treatments by 17.35% and 24.16%, respectively. Relative to RT, the PT treatment resulted in decreased levels of free and crystalline oxides of iron and aluminum, alongside increased levels of amorphous and complexed forms. By contrast, the NT treatment displayed a reverse trend. Redundancy and correlation analyses identified exchangeable Ca²⁺ in G1, pH, clay, and TP, along with iron and aluminum oxides, as key environmental factors influencing the transformation pathways among the complex fractions.