Defeat runoff with BMPs and buffer strips
I have both good news and bad news for you. The good news: researchers have determined that turf is an effective filter of chemicals. This is probably not surprising to you, but it leads to the bad news. Despite these positive research results, communities are restricting or banning some pesticides and “unnatural” or inorganic fertilizers. It is imperative that superintendents educate the public about how turf is consistent with environmental stewardship. More than that, however, they must implement cultural practices that reflect a concern for good stewardship. These practices will help us protect our environmental resources and vindicate our profession.
When you apply fertilizers and pesticides to turf, the fate of these chemicals depends on various factors. If you apply chemicals correctly, the majority is taken up by the target plant or pest. Research shows that most of the rest is rapidly degraded by microorganisms into non-harmful, naturally occurring chemical forms like carbon dioxide, water and oxygen. However, pesticides and nutrients can volatilize into the atmosphere, leach into groundwater or enter surface water via runoff. This article addresses best management practices that you can use to reduce and hopefully eliminate surface nutrient and pesticide runoff.
Factors affecting pesticide and nutrient loss to runoff
Several factors can affect the loss of pesticides and nutrients in surface runoff. Some are controllable while others are subject to the vagaries of nature.
Amount and duration of rainfall or irrigation. Even the best weather technology cannot always predict nature. However, you should have access to current weather-tracking data when making application decisions. Know the extent of predicted rainfall and how long it is expected to last.
Install lower-volume sprinklers with individual head control near surface water features. These components will give you more control over how much water is applied to your turf near sensitive areas.
Soil moisture content prior to rainfall or irrigation. Avoid chemical applications when the ground is saturated with moisture. This is probably the best and simplest way to reduce the potential for surface runoff contamination. Researchers at Oklahoma State University found that runoff occurred as much as six times earlier and total runoff volume was as much as 16 times greater when significant rainfall had saturated the soil prior to a simulated rainfall than when no rainfall occurred.
Length of time between application and next rainfall or irrigation event. Some pesticides and most fertilizers work best if you water them in following application. However, others require a period of dryness for maximum uptake and effectiveness. Consult the chemical label or instructions for this type of information. Although you may want to time a fertilizer application prior to an impending rainfall event, consider the consequences. If a torrential downpour occurs, you may incur significant losses to surface runoff. Consider watering in the product with your irrigation system instead. If you are applying herbicides, be aware of the rainfastness of the product you are using so that you avoid runoff losses and the need for a repeat application.
Method of chemical application. With pesticides, consult the label to find out if more frequent applications at lower rates are an option. Also, spoon-feed fertilizer on areas adjacent to surface-water features. Use the same process of spoon-feeding that you use for other areas of turf such as putting greens.
Timing of chemical application in regard to uptake by plant or target pest. Is there a best time of day to apply pesticide or fertilizer to minimize surface runoff? The answer to that question may depend on the properties of the chemical and its target. Of course, you should restrict your chemical applications to times when winds are calm. If rapid drying ensures optimal uptake, then make applications in the morning. This will increase the opportunity for drying during the day.
Chemical properties of the pesticide or nutrient. Know the physical and chemical properties of pesticides and fertilizer formulations that you apply. This is critical to understanding the potential for loss to surface runoff.
Sorption coefficient. An important value that determines a chemical's likelihood of runoff is sorption coefficient (K
oc). The K ocvalue is an indication of a chemical's ability to bind to organic or inorganic constituents in the turf canopy or soil. A chemical with a low K ocis less likely to adsorb to soil, thatch or turf and, therefore, is more likely to enter runoff. Contact your local extension office for information on relative leaching and runoff potential indices that are based on these factors. They will help you factor potential environmental fate into your application decisions.
Organic vs. inorganic N. The potential for nitrogen loss into the atmosphere or into ground or surface water should not be different for natural organic forms compared to synthetic organic or inorganic forms.
Rate of chemical degradation or transformation. The time (days) necessary for 50 percent of a pesticide to degrade is called its Field Half-Life. The longer a pesticide exists in a reactive form, the greater chance it has to enter runoff. However, a long half-life is essential to the efficacy of some pesticides such as pre-emergence herbicides. Fortunately, most pre-emergence herbicides are highly insoluble and not prone to runoff.
Soil properties. Surface runoff is more likely to occur in turf or vegetation grown in heavy, clay soil than in sandy soil. Soil properties that increase infiltration and water-holding capacity will decrease runoff losses. Although a preliminary study conducted at Oklahoma State University did not show reduced chemical runoff from turf that received deep-tine aerification, in principle, any cultivation or management practice used to improve infiltration and percolation should help reduce surface runoff.
Reducing surface runoff with buffer strips
Surface runoff occurs when the rate of rainfall or irrigation exceeds the soil's infiltration rate. Buffer strips are used in both agriculture and forestry for controlling surface runoff by giving it more time to infiltrate. In turfgrass settings, these take the form of untreated vegetation between a surface-water feature and an area of turf that is managed with fertilizer and pesticide inputs. Buffer strips help to reduce surface runoff by:
Increasing potential for infiltration.
Reducing surface-flow velocity, thus reducing erosion.
Providing physical filtering of sediments.
Diluting applied chemicals.
Two factors are inherent to the success of the buffer strip in achieving the goal of reducing runoff:
The width of buffer strips. How wide should a buffer strip be? There is no single answer to this question. First, check with your local or state agencies to find out if there are any laws or regulations governing the width of buffers in your area. Ask specifically about wetlands; they are often governed by stiffer regulations. Aside from that, the steeper the slope adjacent to the water feature, the greater potential for runoff and the wider the buffer should be. Also, low-lying drainage areas where runoff concentrates should have a wider buffer strip than adjacent areas. Researchers at Oklahoma State University found that buffer widths from 8 to 16 feet were successful in eliminating nearly all nutrient and pesticide runoff when soil moisture was low to moderate. However, when soil moisture was high, these buffer strips were not as effective due to less infiltration.
The type of vegetation. Researchers generally recommend tall, dense vegetation for buffer strips. Investigators at Oklahoma State University discovered that bermudagrass turf mowed at 3 inches was more effective in reducing runoff of pesticides and nutrients than turf mowed at 0.5 or 1.5 inches. It was evident from this research that the tallest-cut bermudagrass buffer strip physically impeded surface runoff.
Most buffer-strip research has concentrated on agricultural applications. Agriculture researchers at Iowa State University suggest that sod-forming grasses work better than clump-type grasses. However, they also report that clump-forming native prairie grasses work well. Tall fescue may also be an ideal species. It forms a thick, rigid turf, and researchers have used it to effectively filter runoff.
The success of buffer strips depends more on site characteristics, local weather and cultural practices than on a pre-defined width and vegetation type. Therefore, you must use buffer strips in conjunction with Best Management Practices (BMPs) to achieve the best results.
Reducing chemical runoff from your turf is a matter of implementing sound agronomic practices and common sense. When it comes to environmental stewardship, let your actions speak for themselves.
Dr. Jim Baird is an agronomist in the Northeast Region of the United States Golf Association, Green Section (Easton, Penn.).
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