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Influence of Atrazine on Denitrification in Soil Columns¹

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.

Key Words: nitrous oxide • herbicides • nitrogen gas • nitrogen fertilizer

¹ Research in part conducted under Int. Atomic Energy Agency Research Agreement no. 2546/CF.

² Soil Scientist, Inst. for Soil Chemistry, CNR, Pisa, Italy; and Professor of Soil Science, Dep. of Land, Air, and Water Resources, Univ. of California, Davis, CA 95616.

Received for publication June 28, 1982.