Effectiveness of zeolite, biochar, and dicyandiamide in reducing nitrogen losses (N 2 O emissions and NH 3 volatilizations) from farming dairy effluent under drought

The combination of farming dairy effluent (FDE) with mitigating agents’ nitrogen (N) losses to the environment, such as zeolites, dicyandiamide (DCD), and biochar, may reduce losses and improve N availability to plants. A field experiment was conducted in an Argiudol of the Pampa region, Argentina, to evaluate N use efficiency and associated losses following FDE application. On a natural grassland with a predominance of ryegrass (Lolium multiflorum) and the presence in smaller quantities of fescue (Festuca sp.), alfalfa (Medicago sativa), and white clover (Trifolium repens). The treatments included application of FDE, FDE plus zeolite (Zeo), FDE plus dicyandiamide (DCD), FDE plus biochar (BC), and a control untreated soil (C), each with three replicates. A uniform application of 11 L m -2 of effluent (eq to 250 kg of N ha -1 ) was performed, and nitrous oxide (N₂O) emissions, ammonia (NH₃) volatilization, soil and atmospheric temperature, and water-filled pore space were monitored up to three months. Overall, N₂O emissions were low across all treatments, reaching a maximum of 18.4 µg m 2 h -1 of N-N 2 O. Zeo and BC significantly reduced N₂O emissions by 63.1 and 63.8 %, respectively, compared with FDE alone. Furthermore, BC reduced NH₃ volatilization by 55.5 % relative to FDE, highlighting its strong potential to mitigate total N losses. Regarding pasture performance, the highest greenness index was observed in the BC treatment, followed by intermediate values in FDE, DCD, and Zeo, and the lowest in the control. Under our study conditions, with particularly low rainfall and high temperatures, the mitigating effects of DCD and Zeo appeared to be limited. In contrast, the combination of FDE and BC emerged as the most effective strategy to reduce N losses and enhance pasture quality. Furthermore, environmental conditions play a key role in determining the efficacy of mitigation strategies to curb N losses.