Proper use of fertilizers minimizes environmental effects

Increasingly, government agencies and society in general are placing a high priority on natural resources, and water in particular. Maintained turfgrass, from roadsides to putting greens, encompasses a considerable portion of the landscape. Therefore, public concern about the environmental fate (especially in water) of management inputs to turfgrasses (particularly fertilizers and pesticides) receives significant media attention.

As a result of this attention, both government agencies and the private sector have funded considerable research examining point- and non-point-source pollution. Research also has focused on identifying and developing "best management practices" that minimize the polluting potential of land-management activities.

Even though researchers throughout the country have conducted a significant amount of research on this topic, from on-site monitoring to small plot projects, the mass media have reported little, if any, of the results to the public. Quite possibly, one of the reasons for the limited press is due to the fact that the results have not been particularly negative. Indeed, the use of grasses as vegetative buffers has long been a standard "best management practice" in many situations, such as decreasing runoff pollution from roads, farmland and feedlots. For example, the use of such filter strips (often sodded) is recommended in the Best Practice Manuals for Construction Related Activities (West Chester County Planning Office, West Chester, Pa.).

Civil engineers and hydrologists also have begun to include seeded or sodded grassed "infiltrating conveyances" as part of their design for storm-water management systems. These open, vegetated portions of the storm-water system slow the rate of overland storm-water flow, allowing sediment and other particulates to deposit themselves onto the vegetation. Once deposited into the grass system, the material no longer moves toward any receiving body of water. In addition, interaction with the biological (primarily microbial) component of the grass system occurs, which serves to decompose or chemically convert various pollutants, thus removing them as a component of the storm water. Also, as a result of reduced flow rate, more of the storm water can infiltrate, thus contributing to ground-water recharge rather than allowing it to enter a stream or other body of water which could remove it from the watershed. For these reasons, the potential contribution of turfgrasses to water-management practices in suburban and urban watersheds is perhaps even greater than for those uses that have long been recognized (production agriculture for example).

A preponderance of evidence clearly shows the value of grassed buffers and virtually no negative impact from the proper application of fertilizers to turfgrass. The fact remains, however, that environmental sensitivity and stewardship should be paramount in your selection and application of turfgrass fertilizers. Some fertilizers and application methods are more appropriate than others in environmentally sensitive areas, and you should design your program accordingly.

Nitrogen (particularly nitrate) and phosphorus are the two nutrients that commonly appear in water resources. As a result, the government has established allowable limits of these nutrients for health- and watershed-protection purposes. Let's examine management practices and fertilizer types in light of environmental concerns.

Nitrogen To be a good environmental steward and use fertilizers correctly, an understanding of nitrogen (N) sources and site conditions is necessary. A proliferation of N sources for use on turf has occurred during the past several years, and these materials vary greatly in terms of their N-release characteristics and method of application. In other words, as most turfgrass managers know, not all fertilizers are the same.

Some forms of N are highly soluble in water. These quickly available types can rapidly provide large amounts of N to turf. However, their high solubility also means that heavy rain or irrigation can dissolve much of the N, possibly carrying it off site via leaching through highly permeable soil or over land as surface runoff if the soil has low infiltration.

Other N sources--slow-release fertilizers--are not so soluble. These types dissolve in water only slowly, limiting the amount that can be released at one time. Thus, a heavy rain or irrigation will not result in large amounts of dissolved N in leachate or runoff. Similarly, coated slow-release fertilizers supply only limited amounts of N on a gradual basis (even though the fertilizer inside could be a highly soluble form). For these reasons, and because turf generally can use N as rapidly as slow-release forms make it available, little N is free to move off site when you use slowly available N. As I'll discuss in the next section, you can use quickly available N sources in an environmentally sound manner, but the overall potential for off-site movement of N is much lower with slow-release sources.

Even on sites where relatively high infiltration rates exist (sandy soil), research shows that the use of slowly available N sources consistently reduces or eliminates the potential for significant leaching of nitrates. Turfgrass roots are highly efficient at extracting nutrients from the soil solution, and organic matter strongly adsorbs fertilizer compounds. Therefore, as long as levels remain moderate, as with slow-release fertilizers, little N is likely to get past the root zone.

Slowly available N also is beneficial for compacted or other slowly infiltrating sites. Slowly available sources of N minimize the potential for off-site movement of nitrate in runoff water by limiting the amount of soluble N available at any given point in time.

Obviously then, slow-release sources are best for minimizing off-site movement of N. The table on page 72 lists some rapid- and slow-release N sources available for turfgrass fertilization.

Regardless of your soil's infiltration rate, your application options for slowly available N sources include either spreader or sprayer.

You can make liquid applications of quickly available N sources, such as urea or ammonium sulfate, to environmentally sensitive sites. However, if you use such sources, the N rate should be light (0.3 pounds or less of actual N per thousand square feet) and the application volume should be low to ensure that the turfgrass canopy intercepts all or nearly all of the application. Relatively complete canopy interception and subsequent foliar absorption of the N minimize the potential for any offsite movement or leaching of nitrate.

Quick-release granular products have relatively high N percentages, which make their application at low rates nearly impossible due to difficulties in uniform granule distribution.

Minimizing the effects of fertilizer use on water resources also includes a lot of common sense. For example, ensure that you do not directly deposit fertilizer, regardless of release characteristics or method of application, into adjacent water sources. Maintaining a non-fertilized buffer strip also is a good practice for protecting water. Buffer strips help absorb nutrients present in runoff as well as add a margin for application error.

You also should be careful not to apply fertilizer to surfaces such as driveways, parking lots and sidewalks. This is a greater risk with broadcast spreaders but also is relevant to liquid applications. Load spreaders on an impervious surface where you can effectively clean up a spill. Conversely, it's better to fill spray tanks on grassed surfaces. Clean both types of application equipment on a grassed surface to prevent movement of rinsate to storm drains or bodies of water.

Phosphorus The presence of phosphorus (P) in water primarily is a concern due to the resulting algal blooms, which can devastate fish and other organisms, and upset the ecology of aquatic systems. However, P generally moves via sediment, and research has thoroughly documented that in established turf, sediment movement in runoff is extremely low. Further, what little movement does occur is at least partly due to atmospheric deposition of particulates onto the turfgrass leaf canopy. The relative insolubility of P, soil and organic-matter adsorption, and lack of erosion are the principle reasons that P applied to established turf does not appear to contribute significantly to elevated P levels in water resources.

When significant movement of land-applied P to surface waters does occur, it is almost always due to soil erosion because P adsorbs onto soil particles. Grass buffer strips are an effective way to decrease the movement of P in runoff sediment. Such buffers are especially important in areas where turf is being established because starter fertilizers (which may contain more P than typical fertilizers) may be present and erosion can more easily occur due to lack of ground cover. Once the turf has become established, you should only determine application rates for P by soil-test recommendations.

Fertilize responsibly It should go without saying that the improper use of fertilizers on turfgrass sites can decrease the quality of runoff and leaching water. Research that has mimicked bad management practices (application of unnecessarily high rates of soluble N sources to saturated soil followed by excessive irrigation) has resulted in the significant movement of N sources. However, research also shows that proper and careful fertilizer applications to turfgrass sites will not put our water resources at risk. In practice, this means observing the following precautions:

* Install unfertilized buffer strips between fertilized turf and surface water or runoff channels

* Use slow-release products.

* If you use quick-release products, use relatively low rates.

* Load spreaders on impermeable surfaces to ease cleanup of spilled material.

* Load sprayers on grassed surfaces.

* Avoid application of any fertilizer to non-target areas such as sidewalks, driveways or roads.

* Rinse sprayers and spreaders on grassed areas to prevent runoff of the rinsate.

* Maintain generally healthy, dense turf.

Despite positive research findings, some local governments have gone so far as to enact ordinances banning the application of P to established turfgrass sites in the belief that this will lower the P concentration in certain water resources. Therefore, it's crucial for turfgrass managers to use fertilizers carefully to avoid providing over-vigilant "watchdogs" with reason to criticize. If you use caution and common sense, the research is on your side, but you must demonstrate that you care for the environment as much as everyone else.

Dr. Thomas L. Watschke is professor of turfgrass science at the Pennsylvania State University (University Park, Pa.).

* Use buffer strips in environmentally sensitive areas. * Use slow-release fertilizer products. * If you use quick-release products, use relatively low rates. * Load spreaders on impermeable surfaces to ease cleanup of spilled material. * Load sprayers on grassed surfaces. * Avoid accidental application of fertilizer to sidewalks, driveways or roads, or other non-target areas such as any body of water. * Rinse sprayers and spreaders on grassed areas to prevent runoff of the rinsate. * Maintain healthy, dense turf.

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