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

Abstract

The combination of farming dairy effluent (FDE) with mitigating agents’ nitrogen (N)losses to the environment, such as zeolites, dicyandiamide (DCD), and biochar, may reducelosses and improve N availability to plants. A field experiment was conducted in an Argiudol ofthe Pampa region, Argentina, to evaluate N use efficiency and associated losses following FDEapplication. On a natural grassland with a predominance of ryegrass (Lolium multiflorum) andthe presence in smaller quantities of fescue (Festuca sp.), alfalfa (Medicago sativa), and whiteclover (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), eachwith three replicates. A uniform application of 11 L m-2 of effluent (eq to 250 kg of N ha-1) wasperformed, and nitrous oxide (N₂O) emissions, ammonia (NH₃) volatilization, soil and atmospherictemperature, and water-filled pore space were monitored up to three months. Overall, N₂Oemissions were low across all treatments, reaching a maximum of 18.4 µg m2 h-1 of N-N₂O. Zeoand BC significantly reduced N₂O emissions by 63.1 and 63.8 %, respectively, compared withFDE alone. Furthermore, BC reduced NH₃ volatilization by 55.5 % relative to FDE, highlightingits strong potential to mitigate total N losses. Regarding pasture performance, the highestgreenness 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 lowrainfall 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 reduceN losses and enhance pasture quality. Furthermore, environmental conditions play a key rolein determining the efficacy of mitigation strategies to curb N losses.