PIG SLURRY AMENDMENT AND HERBICIDE COAPPLICATION EFFECTS ON S-TRIAZINE MOBILITY IN SOIL - AN ADSORPTION-DESORPTION STUDY

Amendments with pig slurry containing dissolved organic matter (PSDOM) and herbicide coapplication are agronomical practices that can influe nce the mobility of herbicides through the soil profile, thus enhancin g the risk of groundwater pollution. Batch equilibrium experiments wer e conducted on a clay loam soil to quantify the influence of these pra ctices on the sorption and desorption of three s-triazine herbicides: atrazine oro-4-ethylamino-6-isopropylamino-1,3,5-triazine), prometryn (2,4-bis (isopropylamino)-6-methylthio-1,3,5-triazine), and terbuthyla zine -butylamino-4-chloro-6-ethylamino-1,3,5-triazine). Soil adsorptio n and desorption capability for atrazine was reduced when it was appli ed with the other two s-triazines in the batch experiment solution. Th e PSDOM treatment immediately after atrazine application had a greater enhancing effect on its desorption than treatment with a 0.01 M CaCl2 solution alone. No enhanced desorption effect was observed on any of the three s-triazines when PSDOM treatment was carried out after repea ted 0.01 M CaCl2 treatments. Soil treatment with PSDOM before atrazine application enhanced soil adsorption capability for the herbicide. On calculating the balance between the adsorbed and desorbed atrazine in the PSDOM-treated soil, a fourfold increase of the atrazine retained was observed. Therefore, to reduce the risk of groundwater s-triazine pollution, pig slurry should be applied to the soil before herbicide t reatment.