One answer to the issue of funding water-quality solutions is right in front of us: Tax the pollutants.

The pollutants are Nitrogen (N) and Phosphorus (P). This is well established by the Iowa Nutrient Reduction Strategy (NRS) that Governor Terry Branstad and the farm industry support. The NRS blames N and P for the pollution that harms Iowa waters and causes the hypoxic or dead zone at the bottom of the Mississippi River.

More than 90 percent of N and two-thirds of the P come from non-point sources, almost all agriculture, according to Iowa State University.

And there is a lot of it. The U.S. Department of Agriculture’s latest Census of Agriculture (2012) shows about $2.6 billion was spent on “commercial fertilizer, lime and soil conditioners” in that year in Iowa.

Yet, while debate proceeds on how to deal with the pollution caused by those chemicals, it is worth noting that normal Iowa sales tax does not apply to the N or P used in agriculture.

I just stopped by the Mount Vernon Ace Hardware to ask if I, a non-farmer, would pay tax on the standard Scotts 10-10-10 garden fertilizer they sell. I would. But farmers do not pay sales tax for theirs. (There is a small fee on chemicals, including N and P for groundwater protection programs, but no general sales tax.)

Since the debate about how to pay for cleaning our waters is in full swing (this paper had no fewer than six opinion articles on the subject last Sunday) it is time to propose the obvious. Since N and P are the culprits, let’s tax them at the same rate as, say, pickup trucks.

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Just like all Iowans do, farmers pay a 5 percent tax on the pickups they use on the farm and off, to pay for their impact on the roads we all use. Since their fertilizer is used on the farm but also flows into the rivers and streams and lakes we all use, costing us all, a similar tax on fertilizer makes sense.

A 5 percent tax on the $2.6 billion in annual farm fertilizer sales in Iowa would bring in roughly $129 million a year, close to the numbers being thrown about to address water quality in the state. It is roughly comparable to what would come from three-eighths of a cent on the general sales tax for the Natural Resource and Outdoor Recreation Trust Fund that Iowa taxpayers approved — but which legislators have refused to fund. Over the next 30 years the fertilizer fee would bring in something close to what the Governor wants to take from a tax designed for school infrastructure.

Why not the obvious solution? Tax the chemicals that pollute Iowa waters.

• David Osterberg of Mount Vernon writes on environmental issues for the nonpartisan Iowa Policy Project, which he co-founded in 2001. He is a former state legislator who was chair of the House Agriculture Committee. Comments: dosterberg@iowapolicyproject.org