DAIRY MANURE INCORPORATION STIMULATES RAPID ATRAZINE MINERALIZATION IN AN AGRICULTURAL SOIL

The herbicide atrazine loro-4-ethylamino-6-isopropylamino-1,3,5-triazi ne) is widely used in the production of corn and several other crops. It is moderately mobile in soil and is frequently detected in surface water and groundwater. The objective of this study was to determine if incorporating manure into a soil cropped to corn influenced the rare or pathway of atrazine dissipation. Soil cores (0-60 cm) were taken fr om two field plots in continuous corn, one unfertilized, the other rec eiving an annual application of 100 t manure ha(-1) for each of the la st 4 yr. The cores were sectioned into 20-cm increments, and subsample s used to prepare soil slurries amended with 2.5 to 25 mu g atrazine m L(-1) slurry. These were incubated with shaking at room temperature fo r up to 2 mo. Chemical analysis of extractable atrazine revealed that the herbicide was completely and rapidly degraded after a variable lag period of as short as about 18 d. Samples from each of the three dept hs degraded atrazine. [U-Ring-C-14]atrazine was quickly and completely converted to carbon dioxide through the intermediate of hydroxyatrazi ne by activated soil slurries. The lag period prior to atrazine remova l was significantly shorter in soil from the manure-treated plot. Stab le enrichment cultures transferred at weekly intervals continued to mi neralize atrazine confirming that atrazine-metabolizing microorganisms were responsible for atrazine degradation in this soil.