|Blanchard, Paul - MO DEPT OF CONSERVATION|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 30, 2005
Publication Date: October 1, 2005
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/36221500/cswq-0185-174337.pdf
Citation: Ghidey, F., Blanchard, P.E., Lerch, R.N., Kitchen, N.R., Alberts, E.E., Sadler, E.J. 2005. Measurement and simulation of herbicide transport from the corn phase of three cropping systems. Journal of Soil and Water Conservation.60(5):260-273. Interpretive Summary: Herbicides moving in surface runoff from agricultural cropland degrade downstream surface water supplies. Reducing such nonpoint source (NPS) pollutants requires cropping systems that successfully balance economic profitability with multiple environmental considerations. We measured differences in herbicide concentrations and loads (i.e., the total mass of herbicides leaving a field) among three cropping systems and developed an equation that would be useful in predicting herbicide concentrations and loads. The 6-year study was conducted on large plots farmed with modern machinery that were instrumented to measure the amount of surface runoff and to collect samples for herbicide analyses. Cropping system 1 (CS1) was a conservation tillage system with a corn-soybean rotation, and the herbicides atrazine and metolachlor were incorporated into the soil immediately after application. Cropping system 2 (CS2) was a no-till system with a corn-soybean rotation, but the applied herbicides were not incorporated. Cropping system 5 (CS5) was a no-till system with a corn-soybean-wheat rotation, and herbicides were not incorporated. CS5 was an adaptive system in which herbicide application was tailored to existing weed pressure. The presence of wheat stubble in this system allowed us to reduce herbicide application rates for adequate weed control, and, in addition, we adjusted the timing of application as needed. In all cropping systems, herbicide concentrations in the first runoff event following application were always high, but concentrations rapidly decreased in subsequent events. Incorporation consistently reduced herbicide concentrations from CS1 (herbicides incorporated) compared to CS2 (herbicides not incorporated). The reduced-tillage systems caused greater overall losses of herbicides due to lack of incorporation and slightly higher runoff volumes. Using the data from this study, we were able to develop a predictive equation that will be useful in other field settings. Our results will be useful to farmers, extension/education personnel, and national and state agencies responsible for maintaining and/or improving surface water quality by providing relevant information about the effects that crop management practices have on herbicide transport.
Technical Abstract: Herbicide transport in surface runoff can contaminate drinking water supplies and degrade aquatic habitat. The objectives of this study were to determine the effects of different cropping systems on herbicide transport in surface runoff and to develop a generalized equation that can estimate herbicide concentrations or loads as a function of time after application, runoff volume, and application rate. The study was conducted from 1997 through 2002 on 0.34-ha plots instrumented with Parshall flumes and automated samplers equipped with pressure transducers to measure stage height. Three cropping systems were evaluated: 1) a mulch tillage corn-soybean rotation where herbicides were broadcast at planting and incorporated (CS1); 2) a no-till corn-soybean rotation where herbicides were broadcast at planting and not incorporated (CS2); and 3) a no-till corn-soybean-wheat rotation where herbicides were broadcast at reduced rates, not incorporated, and herbicide application rate and timing varied (CS5). The study focused on atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and metolachlor [2-chloro-N-(-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethy)acetamide]. Surface runoff from the corn phase of each rotation was sampled from the date of application to grain harvest. Dissolved atrazine and metolachlor concentrations in runoff were determined with enzyme-linked immunosorbent assays (ELISA). No-till systems resulted in slightly greater runoff volume than the tilled system. For all cropping systems, atrazine and metolachlor concentrations in surface runoff were extremely high soon after application, but decreased exponentially with time. Herbicide incorporation (CS1) significantly reduced atrazine and metolachlor loads compared to the corresponding no-till system (CS2). Comparisons between the no-till systems showed that split atrazine application in CS5 resulted in 50% higher atrazine load than CS2. Reduced herbicide application rates did not significantly reduce atrazine loads, but metolachlor loads were reduced by 35% in CS5 compared to CS2. Relative herbicide loads ranged from 1.3 to 3.6% of applied for atrazine, and from 1.0 to 1.7% for metolachlor. No-till systems resulted in greater overall losses of herbicides due to lack of incorporation and slightly higher runoff volumes. The developed equation typically fit the concentration or load data well (r**2 ranged from 0.45-0.82), and the equation should have utility at other locations and scales. A key management challenge for these soils is to find a cropping system that facilitates herbicide incorporation but leaves sufficient crop residue to control soil erosion.