Influence of Atrazine on Denitrification in Soil Columns

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Abstract
The effects of the herbicide atrazine (2‐chloro‐4(ethylamino)‐6‐(iso‐propylamino)‐s‐triazine) on denitrification was evaluated during steady transport of 15N‐nitrate through 0.15 m long columns of San Cataldo silt loam (Fluvisol, according to the FAO world map legend) and Yolo loam soil (Typic Xerorthents). The soil atmosphere was maintained at a small O2 partial pressure by flowing a gas mixture of 70% He and 30% N2 through plastic jackets surrounding the plastic soil columns, which had many holes (1 mm diam) drilled through the column sides. This column design allowed evolved N2 and N2O gases to be measured in the effluent gas of each column. The nitrate (NO3−) concentration in the solution effluent and the evolved gases from columns with added atrazine (3 mg kg−1) were compared with that from columns without atrazine. Nitrate reduction rates were determined from a mathematical solution of transport and transformation of nitrate according to first‐order kinetics. The presence of atrazine in the soils resulted in slightly increased nitrate reduction rates over that of the controls. Atrazine caused a decrease in the N2/N2O ratio of the evolved gases. A small amount of NO was also detectable in San Cataldo column without atrazine. The apparent inhibition of N2O reduction by atrazine may have environmental implications in relation to N2O release from the soil to the atmosphere.