Fate of Copper in Saline–Alkali Soil with Long-Term Application of Biogas Residue

The retention of copper (Cu) in saline–alkali soil (SAS) during long-term application biogas residue (BR) with a high concentration Cu raises concerns. In this work, the fate was detected using adsorption isotherms, scanning electron microscope—energy dispersive spectrometer, Fourier transform infrared X-ray diffraction, isothermal titration calorimetry, photoelectron spectroscopy, and microzone fluorescence spectrometer. results showed that main groups for by SAS BR were carboxyl, hydroxyl, amide amine. carboxyl group entropy–enthalpy co-driven (|ΔH| < |TΔS|, ΔH 0). amine entropy-driven > on achieved organic matter rather than minerals. degradation increases content such as groups, adsorbed surface or inside through groups. This study provides further theoretical support SAS.