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 an d herbicide application methods on crop residue cover, surface runoff volum e, 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-methylphen yl)-N-(2-methoxy-1-methylethyl)], and cyanazine [2-((4-chloro-6-(ethylamino )-1,3,4-triazin-2-yl)amino)-2-methylpropionitrile]) losses were measured fr om continuous corn runoff plots (1.7 x 12.0 m long) in 1993 and 1994. Four tillage/herbicide application treatments were studied: no-till/herbicide br oadcast sprayed (NT), fall chisel plow-spring disk/herbicide broadcast spra yed after disking (DS), fall chisel plow-spring disk/herbicide broadcast sp rayed before disking (SD) and fall chisel plow-spring "mulch master"/herbic ide applied with John Deere's Mulch Master (MM). Results showed that herbic ide incorporation with the MM and SD treatments reduced herbicide losses. R esidue measurements after any tillage and planting showed that percent resi due cover was greatest on NT plots, second on MM plots, and least and simil ar on SD and DS plots. By runoff event, NT plots generally had the least er osion and often the lowest runoff volumes. Herbicides concentrations in bot h 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 run off 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 inc orporation and/or more interception with the greater crop residue with NT w ere 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 los ses with NT by event were variable, sometimes being the greatest, sometimes the least; depending primarily on runoff volumes, which in rum were depend ent on the storm volume and intensity, and the time of year; however, for t he other three treatments, losses were usually in the order DS > MM > SD. ( C) 2001 Elsevier Science B.V. All rights reserved.