Atrazine transformation during corn stover ensiling and its impacts on the ensiling microbiome and feed safety

Atrazine is a triazine herbicide widely used in maize production, and residues in corn stover intended for feed may compromise forage safety. However, the fate of atrazine under ensiling conditions and its relationships with the fermentation microbiome remain poorly understood. Corn stover harvested at the wax-ripe stage was assigned to an untreated control (CK) and three atrazine-spiked treatments at 0.5 mg/kg fresh matter (FM; 1b), 2.5 mg/kg FM (5b), and 5.0 mg/kg FM (10b). Samples were collected after 0, 3, 7, 15, 30, and 60 d of ensiling to quantify parent atrazine (ATZ) and its major transformation products hydroxyatrazine (HA), deisopropylatrazine (DIA), and deethylatrazine (DEA). Nutritional composition, fermentation quality, and aerobic stability were also determined, and bacterial and fungal communities were characterized by 16 S rRNA gene and ITS sequencing, respectively. The main findings were as follows: (1) ensiling markedly reduced parent ATZ residues, but this dissipation was accompanied by HA accumulation; therefore, a decline in parent ATZ concentration does not necessarily indicate a concomitant reduction in ecological or safety risk. (2) ATZ residues had limited effects on final nutritional and fermentation quality, whereas high-residue treatments affected the aerobic stability of silage after opening. Importantly, this prolongation of apparent aerobic stability should not be interpreted as an improvement in silage quality or feed safety.