Tillage impact on herbicide loss by surface runoff and lateral subsurface flow

Authors: Potter, Thomas; Bosch, David - Dave; Strickland, Timothy - Tim

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2015
Publication Date: 6/5/2015
Citation: Potter, T.L., Bosch, D.D., Strickland, T.C. 2015. Tillage impact on herbicide loss by surface runoff and lateral subsurface flow. Science of the Total Environment. doi: 10.1016/j.scitotenv.2015.05.079.

Interpretive Summary: Soil management focused on improving soil health and reducing surface runoff, sediment, and agrichemical loss from farm fields often depends on the family of practices known as conservation tillage. These practices are effective in part because they promote increased inflation of rainfall and irrigation into the soil. In some landscapes this may result in increased movement of water through a process termed “lateral subsurface flow”. This occurs when infiltrating water reaches a subsurface soil horizon with reduced permeability. The water is then redirected down slope across the surface of this layer. Hence the term “lateral subsurface flow”. Typically it emerges at the base of slopes in wetlands and or is directly discharged into surface water bodies. Transport of water soluble contaminants such a nitrate and selected pesticides to these sensitive environments may result. Our investigation focused on determining whether use of a common conservation tillage practice during cotton and peanut production in the Atlantic Coastal region of the southeastern USA may increase subsurface transport of fluometuron, an herbicide commonly used in cotton production. Data were collected over 11 years at an intensely monitored field site we maintain in south central Georgia. Results showed that increased fluometuron transport in the subsurface may be observed when conservation tillage is used. While losses were increased they were still relatively small when compared to potential losses in surface runoff when conservation tillage practices were not used. Taking both surface and subsurface transport losses together showed that conservation tillage use during rotational cotton and peanut production decreased total fluometuron loss by more than 2- fold. This provides additional support for increased use of conservation tillage practices in the region.

Technical Abstract: There is worldwide interest in conservation tillage practices because they can reduce surface runoff, and agrichemical and sediment losses from farm fields. Since these practices typically increase infiltration, their use may increase subsurface transport of water-soluble contaminants. Thus, to assess long-term environmental benefits of conservation tillage data may be needed that quantify both surface and subsurface contaminant fluxes. This study focused on the herbicide fluometuron (N,N-dimethyl-N'-[3-(trifluoromethyl)phenyl]-urea) and its soil degradate DMF (N-methyl-N'-[3-(trifluoromethyl) phenyl]-urea). Both compounds are classed as “leachable”. They were measured for 10 years in surface runoff and lateral subsurface flow from paired fields located on a hill slope in the Atlantic Coastal Plain region of the southeastern USA. One group of fields was conventionally tilled incorporating all crop residues into soil prior to planting. The second was strip tilled, a common conservation tillage practice. Seven fluometuron applications were made to cotton (Gossypium hirsutum)produced in rotation with peanut (Arachis hypogea). Combined fluometuron and DMF surface and subsurfacelosses from the conventionally tilled fields were equivalent to 1.2% and 0.13% of fluometuron applied and 0.31% and 0.32% from the strip tilled fields. Annual surface runoff losses were significantly greater from the conventionally tilled fields while the strip tilled fields had significantly greater annual subsurface losses. Results demonstrated that shifting from conventional to conservation tillage management of farm fields in this landscape will reduce surface runoff losses of herbicides like fluometuron but subsurface losses will likely increase. The same trends can be expected in landscapes with similar soil and hydrologic properties. This should be considered when planning implementation of programs that promote conservation tillage use.