Editor’s note: This is the final installment in a series of articles on the science behind phosphorus bans increasingly being proposed in state legislatures.
When passing statewide restrictions on phosphorus applications on turfgrass in 2002, Minnesota legislators had the foresight to mandate the state’s Department of Agriculture submit a report to the legislature by January 15, 2007 on the effectiveness of the legislation. As stated in that report, “Changes in water quality resulting from the law have not been documented at this time.”
The report said phosphorus (P) runoff data gathered following the fertilizer restrictions were too variable from year to year to indicate “short-term” (five year) trends in water quality.
A Dane County, Wisconsin ordinance regulating P application on lawns took effect in January 2005. The Dane County Lakes Commission reported in late 2007 there was no evidence at that time of improvements in lake water quality.
Bans’ Effectiveness Doubtful
The experiences of Minnesota and Wisconsin cast doubt on the general effectiveness of P bans. They do not exclude the possibility that in some instances P regulations will improve surface water quality. But improvement due to P bans is likely to happen only for those lakes where runoff water from turfgrass is a major contributor of P and where fertilizer can be identified as a prominent source of that P.
Science, however, tells us instances where all these preconditions exist are likely rare.
Given the experience to date with lawn P bans, it seems reasonable to suggest all such bans should include a sunset clause invoked when there is no evidence of the ban’s effectiveness. Current experience suggests sunset clauses should be set at 10 years.
Dark Side of Bans
Depending on how lawn P bans are crafted, they can have an insidious effect. Enforcement is often and almost universally in the hands of private citizens, as the authorities rely on complaints filed with some designated unit of government.
This approach to enforcement tends to pit neighbor against neighbor.
The Dane County, Wisconsin ordinance prohibits vendor display of lawn fertilizers containing P. One interpretation of this restriction is that the crafters of the ordinance did not trust the sellers and buyers of lawn fertilizers to abide by the ordinance. It also obscures the fact that fertilizers containing phosphorus can be sold and used if soil tests indicate a need for the nutrient.
The requirement that P-containing fertilizers be hidden in a back room helps instill in the minds of citizens the notion that P is very nasty stuff. Such a restriction embodies government distrust of business and disrespect for the intelligence of private citizens.
Phosphorus bans can have unintended consequences, leading to increased P loads in runoff water instead of the intended decreases. The bans discourage soil testing and encourage blind application of “phosphorus-free” fertilizers.
Wisconsin research has shown for medium-textured soils, not applying P leads to an annual 2.3 parts per million decrease in soil test P. Deficiencies will eventually develop and lead to reductions in lawn quality. Given that the density of lawn cover helps the grassy area retain water, research indicates the end result of such bans will be increases in runoff water volumes and, ironically, higher P loads in nearby bodies of water.
Researchers have been given opportunities to present in public forums their perspectives on whether P bans will achieve their intended purpose. They have presented extensive evidence showing P bans will not be nearly as effective as ban advocates have touted them to be.
Unfortunately, the science is routinely being ignored in the final deliberations, leading to passage of ordinances and laws that regulate P applications on turfgrass.
Science Versus Politics
One of the prime reasons for that dynamic is that these decisions are being made by elected government officials.
Put yourself in their place for a moment. Your constituency is very publicly insisting something be done to improve and protect lake water quality. Even though you may not be fully convinced a P ban will be effective, it comes at no or very little direct cost of tax dollars and might placate your constituents.
Under these circumstances, it’s easy to see why lawmakers might support regulation or banning of P applications on turfgrass, even though the science suggests the law might actually be counterproductive.
No Single Action Suffices
Science can lead the way in the development and implementation of actions holding high promise for improving and protecting surface water quality, but each body of water must be treated as an individual occupying a particular position in the landscape. Research is needed to quantify the P dynamics of the lake, establish what changes are required to improve water quality, and identify and quantify all P inputs.
Then and only then can strategies be developed that have a high probability of achieving the desired goal.
Unfortunately, all of this costs money—often lots of money—because multiple, coordinated actions across several government jurisdictions are often required.
A single action such as a P ban is not the answer.
Wayne Kussow, Ph.D. ([email protected]) is an emeritus professor in the Department of Soil Science at the University of Wisconsin-Madison.