title: Corn stover harvest increases herbicide movement to subsurface drains - Root Zone Water Quality Model simulations.
abstract: BACKGROUND
  Crop residue removal for bioenergy production can alter soil hydrologic properties and the movement of agrochemicals to subsurface drains. The Root Zone Water Quality Model (RZWQM), previously calibrated using measured flow and atrazine concentrations in drainage from a 0.4 ha chisel-tilled plot, was used to investigate effects of 50 and 100% corn (Zea mays L.) stover harvest and the accompanying reductions in soil crust hydraulic conductivity and total macroporosity on transport of atrazine, metolachlor and metolachlor oxanilic acid (OXA).
  
  
  RESULTS
  The model accurately simulated field-measured metolachlor transport in drainage. A 3 year simulation indicated that 50% residue removal reduced subsurface drainage by 31% and increased atrazine and metolachlor transport in drainage 4-5-fold when surface crust conductivity and macroporosity were reduced by 25%. Based on its measured sorption coefficient, approximately twofold reductions in OXA losses were simulated with residue removal.
  
  
  CONCLUSIONS
  The RZWQM indicated that, if corn stover harvest reduces crust conductivity and soil macroporosity, losses of atrazine and metolachlor in subsurface drainage will increase owing to reduced sorption related to more water moving through fewer macropores. Losses of the metolachlor degradation product OXA will decrease as a result of the more rapid movement of the parent compound into the soil. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
authors.affiliation: USDA-Agricultural Research Service, Ames, IA, USA.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Shipitalo
authors.affiliation: USDA-Agricultural Research Service, Ames, IA, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Malone
authors.affiliation: USDA-Agricultural Research Service, Fort Collins, CO, USA.
authors.forename: Liwang
authors.initials: L
authors.lastname: Ma
authors.affiliation: US Geological Survey, Reston, VA, USA.
authors.forename: Bernard T
authors.initials: BT
authors.lastname: Nolan
authors.affiliation: Iowa State University, Ames, IA, USA.
authors.forename: Rameshwar S
authors.initials: RS
authors.lastname: Kanwar
authors.affiliation: USDA-Agricultural Research Service, Fort Collins, CO, USA.
authors.forename: Dale L
authors.initials: DL
authors.lastname: Shaner
authors.affiliation: Iowa State University, Ames, IA, USA.
authors.forename: Carl H
authors.initials: CH
authors.lastname: Pederson
mesh_terms: D000081:Acetamides; D001280:Atrazine; D006540:Herbicides; D008962:Models, Theoretical; D058441:Rhizosphere; D014872:Water Movements; D060753:Water Quality; D003313:Zea mays
chemical_list: D000081:Acetamides; D006540:Herbicides; D001280:Atrazine; C051786:metolachlor
keywords: OXA; atrazine; metolachlor; modeling; tile drainage; water quality