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 influence the mobility of herbicides through the soil profile, thus enhancing the risk of groundwater pollution. Batch equilibrium experiments were conducted on a clay loam soil to quantify the influence of these practices on the sorption and desorption of three s-triazine herbicides: atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), prometryn (2,4-bis (isopropylamino)-6-methylthio-1,3,5-triazine), and terbuthylazine (2-tert-butylamino-4-chloro-6-ethylamino-1,3,5-triazine). Soil adsorption and desorption capability for atrazine was reduced when it was applied with the other two s-triazines in the batch experiment solution. The 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 repeated 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 treatment.