Chemical movement in relation to tillage system and simulated rainfall intensity

The Piedmont region in the southeastern USA is characterized by sloping, crust-prone soils conducive to runoff losses of agricultural chemicals. Three tillage-residue management systems were compared for their effect on concentrations of atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine], metolachlor [2-chloro-N-(2-ethyl-6- rnethylphenyl)-N-(2-methoxy-1-methylethyl)] acetamidel, and bromide in surface runoff and in the soil profile of a Pacolet sandy clay loam (clayey, kaolinitic, thermic Typic Kanhapludults). These systems included conventional tillage (CT), no-tillage grain production with corn (Zea mays L.) residue (NTG), and no-tillage silage production without residue (INTS). The first simulated rainfall event consisted of a low (1.27 cm h{sup -1}) or high (5.08 cm h{sup -1}) rainfall rate applied for 30 min following herbicide and bromide application. One week later, the high rate was simulated on all plots. The CT treatment generally produced less surface runoff, and accompanying lower chemical concentrations. compared with both no-tillage treatments on the first date. Runoff differences due to tillage system were less on the second date because of surface sealing processes under CT. Averaged over 2 yr, the percent-age of applied atrazine lost on the first runoff event was 6.2% for NTG, 4.4% for NTS, and 1.5% for CT. Losses of atrazine in runoff on the second date weremore » 1.5, 1.4, and 1.0% of that applied for NTG, NTS, and CT, respectively. The surface 7.5 cm of soil contained the highest concentrations of chemicals for all treatments, with treatment differences occurring primarily in the surface 0 to 15 cm of soil. Lower runoff values under CT generally resulted in higher soil chemical concentrations. 31 refs., 6 figs., 7 tabs.« less