The widespread use of triazine herbicides (TRZs) in global agriculture raises environmental concerns due to their persistence and ecotoxicity, especially in semiarid loess regions where manure amendments introduce external dissolved organic matter (DOM). This study investigates how cattle manure-derived DOM (MDOM) influences the adsorption behavior of two typical TRZs-atrazine (ATZ) and prometon (PRM)-in calcareous loess soils. Through systematic batch experiments controlling pH (3-11), ionic strength (0.01-0.10 mol & sdot;L-1 Ca2+), and cation competition (Ca2+, Na+, Mg2+, K+, NH4+), we identify three key mechanisms: MDOM extends equilibrium times and enhances saturated adsorption capacities, primarily through Ca2+-bridged complexation and it-it interactions with lignin derivatives; Adsorption decreases with increasing pH due to deprotonation-induced electrostatic repulsion; Divalent cations play contrasting roles, with Mg2+ promoting ATZ adsorption but hindering PRM, while monovalent ions universally inhibit adsorption. Spectroscopic analyses validate MDOM's concentration-dependent effects, with low doses enhancing adsorption cooperatively and higher doses triggering competitive site occupation. These results highlight how MDOM alters TRZs' behavior in manure-amended soils, shifting mechanisms from hydrophobic partitioning to chemisorption. The study offers insights for optimizing organic amendments in semiarid farmlands, recommending MDOM dosage thresholds to balance soil fertility enhancement with groundwater protection. This research contributes to predictive models of pesticide fate in calcareous soils and guides sustainable manure management practices in evolving agricultural landscapes.