The turfgrass industry fights back
With a few exceptions, fertilizer containing phosphorus is not allowed for use on lawns, golf courses, athletic fields or other turf sites in Wisconsin beginning in April 2010. Wisconsin will join Minnesota, and New York, which passed similar legislation earlier in banning turfgrass fertilizers containing phosphorous.
The ban restricts the display and use of phosphorus-containing fertilizer, with two exceptions. The first exception is for the establishment of new lawns, and the second exception is when soil tests show a deficiency in phosphorus. Only an organic, low-phosphorus fertilizer is specifically allowed according to legislation wording. While landscapers, lawn professionals and others involved in the turf industry will comply with the ban, the ban is not without controversy. Monroe Miller, executive director of the Wisconsin Turfgrass Association, cites the extensive work of researchers at the University of Wisconsin at Madison in phosphorus issues. Some UWM researchers with a long history of researching the topic approach the phosphorous issue from a different vantage point.
“We can’t win this on science alone,” notes John Stier, professor and chair of the Department of Horticulture at the University of Wisconsin at Madison. Studies have indicated that turfgrass buffers reduce the amount of phosphorus that enters water from runoff, so Stier and associates have evaluated the differences between fertilized turfgrass and unfertilized native prairie plantings and have found little difference in the phosphorus levels of runoff from turfgrass or prairie plantings buffer areas.
Algae also increases with higher levels of phosphorus, which can lead to fish kills, degraded drinking water and negative impacts on recreation. Most researchers agree that reducing phosphorus is the key to curtailing algae growth. While the ban was supported by a number of lake organizations and others interested in protecting water, agreement is benefits of the ban is not universal.
Douglas Soldat, UWM Soil Science Department assistant professor, worked extensively with nutrient management at Cornell University. He says, “Phosphorus is the most limiting of the nutrients and binds tightly to soil.” He notes that erosion is a major contributor to increased phosphorus loads, and cites extensive research conducted at UWM O.J. Noer Turfgrass Research and Education Center, particularly research led by Dr. Wayne Kussow, UWM Soil Sciences Department emeritus professor, and Stier. Research at the Noer Center includes work on various aspects of turfgrass from mowing practices to nutrient management.
Stier says that because of the ban the public perception is that most runoff containing phosphorus that affects surface and groundwater is from lawn fertilizer. “Only about half the lawns have fertilizer at all,” Stier says, noting that of those, most receive fertilizer only about once a year. About 95 percent of the phosphorus used is in agriculture in the growing of row crops. But, Stier notes that even agriculture is not the major contributor to phosphorus-containing runoff.
“That is dwarfed by construction,” he explains. Soil contains naturally occurring phosphorus, and anytime the soil is disturbed, phosphorus that is present is contained in runoff.
The researchers agree that while adding unneeded phosphorus to the soil serves no purpose, most phosphorous-containing runoff does not occur from fertilized turfgrass areas.
Primary sources of phosphorus
Kussow has worked with phosphorus and other issues relating to runoff extensively. According to Kussow, a logical conclusion based on research in Minnesota, New York and Wisconsin is that runoff water phosphorus loads from turfgrass are generally greater than for forests, but do not differ significantly from native vegetated areas such as prairies, and that, on average, the runoff phosphorus load from turfgrass is one-third or less than the load in runoff from agricultural land.
He also notes that phosphorus in fertilizer is from two sources, both of which are water-soluble, meaning that heavy irrigation or rainfalls greatly reduce the amount left on the soil surface, down to about 1 percent of fertilizer phosphorus that can make its way into bodies of water or the water table.
Following this line of reasoning, fertilizer phosphorus is transferred primarily through erosion of phosphorus soil particles referred to as sediment. Kussow cites the high amount of sediment loss from agricultural land that he says is measured in tons per acre, while sediment in turfgrass runoff ranges from zero to 100 pounds per acre. Sediment loss is dependent on density of turfgrass, and if turfgrass cover is around 70 percent, sediment loss is zero, according to Kussow.
Kussow says that sources other than lawn fertilizer often contribute to the high phosphorus level is home lawns. Phosphorus sources in Madison, Wis., as well as most other metropolitan areas, are often tied to housing developments that are on former agricultural land. A common practice is to strip topsoil and stockpile it to be spread on lawns for turfgrass establishment as development is completed. With most of the stockpiled topsoil containing high levels of phosphorus from agricultural applications, the soil can test for high levels of phosphorus without the use of any fertilizer.
While Kussow’s work indicates that lawn fertilizer is not the primary contributor to increased phosphorus loads in surface and groundwater, he says, “Fertilizer is expensive. Agronomically, following the regulation is a sound practice.”
Turfgrass, prairie plantings and buffers
Urban development has greatly increased the amount of hard surfaces and contributed to increased runoff containing various nutrients with phosphorus a primary concern that can contaminate surface water and groundwater, and can be a cause of groundwater depletion. Federal and state laws are in place to limit total suspended solids (TSS) and phosphorus from entering surface waters, and nitrates are regulated in groundwater.
Stier and research associates conducted studies at the Noer Center to evaluate and compare the amount of protection from urban runoff provided by both turfgrass and native prairie plantings. Additionally, the benefits of buffers were tested and the amount of recharge occurring to the groundwater supplies was evaluated.
Rain gardens, depressions in the ground surrounded by berms and planted with native plants, have gained popularity in some areas to collect rooftop or other hard surface runoff. Research results showed that vegetation type had little impact on runoff volume, TSS or phosphorus entering surface waters. Plant density was deemed more important than vegetative type. Rain gardens and lawn turf were tested both with and without berms. The unbermed lawn had similarly low amounts of runoff and of sediment, statistically less than the water and sediment from the unbermed and unfertilized prairie plantings.
Urban buffer strips were evaluated for their potential to increase groundwater recharge and mediate surface water flows. Vegetative buffer strips of at least half the size of an upslope hard surface reduced the volume by half compared with percolate directly from the edge of the pervious service. Research results indicate that although turf buffer strips occasionally yielded greater amounts, both unfertilized prairie and fertilized turf plantings potentially provide similar annual groundwater recharge. Stier and associates concluded that a sufficiently sized vegetative buffer strip moderated the flow, reducing the potential amount of N and P draining to groundwater as water moved off impervious surfaces.
UWM researchers agree that while the ban has little effect on landscapers except in their avoiding the application of starter fertilizer containing phosphorus as has been a common practice, the ban on turfgrass fertilizer focuses too much attention on turfgrass.
Stier says, “We have to get out and tell our story. Landscapers and lawn care professionals need to attend meetings and be sure that their stories get out.” Their stories are important to understanding just what transpires in the scenario that has included increased loads of phosphorus in water leading to issues of concern.
Nancy Riggs is a freelance writer and has been covering the green industry for Turf for almost 20 years. She resides in Mt. Zion, Ill.