Tillage and herbicide incorporation effects on residue cover, runoff, erosion, and herbicide loss

A natural rainfall study was conducted to evaluate the effect of tillage and herbicide application methods on crop residue cover, surface runoff volume, erosion, and herbicide losses with sediment and runoff water. Sediment, water, and three herbicides (atrazine [(6-chloro-N-ethyl)-N-(1-methylethyl-1,3,5 triazine)-2-4-diamine], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)], and cyanazine [2-{{4-chloro-6-(ethylamino)-1,3,4-triazin-2-yl}amino}-2-methylpropionitrile]) losses were measured from continuous corn runoff plots (1.7×12.0 m long) in 1993 and 1994. Four tillage/herbicide application treatments were studied: no-till/herbicide broadcast sprayed (NT), fall chisel plow-spring disk/herbicide broadcast sprayed after disking (DS), fall chisel plow-spring disk/herbicide broadcast sprayed before disking (SD) and fall chisel plow-spring “mulch master”/herbicide applied with John Deere’s Mulch Master (MM). Results showed that herbicide incorporation with the MM and SD treatments reduced herbicide losses. Residue measurements after any tillage and planting showed that percent residue cover was greatest on NT plots, second on MM plots, and least and similar on SD and DS plots. By runoff event, NT plots generally had the least erosion and often the lowest runoff volumes. Herbicides concentrations in both sediment and runoff water were generally in the order NT>DS>MM>SD, with herbicide concentrations 2–10 times higher in sediment than in the runoff water. Since the herbicides used were not strongly adsorbed, more than 95% of the runoff loss in each case was in the dissolved phase. Lack of incorporation and/or more interception with the greater crop residue with NT were believed to be responsible for the higher herbicide concentrations with that treatment. Total losses for all three herbicides each year were less than 2% of that applied, and ranged from 1.5% for atrazine in 1993 to 0.07% for metolachlor in 1994, both for the NT treatment. Relative herbicide losses with NT by event were variable, sometimes being the greatest, sometimes the least; depending primarily on runoff volumes, which in turn were dependent on the storm volume and intensity, and the time of year; however, for the other three treatments, losses were usually in the order DS>MM>SD.