The calculation used to determine how much fertilizer farmers can apply to their crops in Arkansas doesn’t take into account the potential of the fertilizer leaching underground, meaning it doesn’t adequately protect the state’s waterways, critics say.
The Arkansas Phosphorus Index calculates the potential of phosphorous runoff during a rain. The index is largely used by farmers, but recently processing plants and municipal wastewater plants have been using it.
Where the Buffalo River is located, for example, the index doesn’t take into account all of the ways phosphorus can get into waterways, critics say. The area is karst, which often features cracks, fissures and sinkholes that allow substances to trickle down and move underground.
But the variability of karst terrain means karst shouldn’t be factored into the index, said Brian Haggard, director of the Arkansas Water Resources Center at the University of Arkansas, Fayetteville, College of Engineering.
The state’s hog farms — and neighboring fields where hog manure is used as fertilizer — are often in karst areas in north and southwest Arkansas. More often than not, the soil on which the manure has been spread has phosphorous levels that are considered excessive for plant nutrition, according to an
Arkansas Democrat-Gazette
review of the permits and soil analysis samples of about 100 Arkansas hog farms.
It’s the raw soil samples, not the nutritional needs of crops, that pertain most to the index — which is designed to address surface-runoff pollution.
The Arkansas Phosphorus Index assigns a phosphorous-runoff risk value to land upon which a farmer wants to spread animal waste. Manure can be applied only on land deemed to have a “low” or “medium” risk of runoff, according to the Arkansas Department of Environmental Quality.
The phosphorous index multiplies three things together: phosphorus source potential (based on soil tests and the phosphorous application rate), transport potential (how easily phosphorus might move, based on the slope of the land and other elements), and best management practices (such as ponds, fencing or buffers on the land).
Each of the three factors has its own factor that determines its value. Factors are assigned numeric values, even when they are not actual measurements, such as the values for how often an area of land floods (0 for “very rare,” 0.2 for “rare,” 0.5 for “occasional” and 2 for “frequent”). Soil samples help to recalculate the land’s risk every year.
The index was put together by Andrew Sharpley, a professor in the Department of Crop, Soil and Environmental Sciences at the University of Arkansas, Fayetteville; Haggard; and others from the University of Arkansas System and employees of the Arkansas Natural Resources Commission and the U.S. Department of Agriculture.
Last fall, the Arkansas Department of Environmental Quality denied a new operating permit for C&H Hog Farms in Newton County in part because of concerns about karst, phosphorous levels and the impairment of the nearby Buffalo River.
The farm, located in the Buffalo River watershed, has become the focus of environmental groups that believe it is a threat to the national river. Phosphorus can contribute to algal growth in water.
Like many farms, C&H Hog Farms uses the manure its animals produce as fertilizer for its land. Often, farmers send the manure to other farmers who want to use the nutrient-rich material.
Farmers should factor in karst within devising their nutrient management plans, Haggard said. Such plans are required for poultry operations in 13 Northwest Arkansas counties (considered to have excessive nutrients) and hog farms. The plans can be more than 100 pages, and they describe how waste will be contained and disposed of.
Not every karst-susceptible area has karst, Haggard said. Farmers can look for visible signs of karst and determine what needs to be written into their plans, he said.
Manure cannot be applied within 50 feet of a hole, Sharpley said, as an example.
But karst areas, which have little topsoil, can often include cracks underground that don’t appear on the surface, said Gordon Watkins, president of the Buffalo River Watershed Alliance. That means phosphorus could leach into the ground faster and end up falling through cracks and into waters, he said.
Watkins acknowledges phosphorus is retained in soil better than are some other nutrients. But, he said, that “legacy phosphorus” can leach for decades underground or through surface runoff.
“Legacy phosphorus” has been cited as a continuing contributor of phosphorus in the Illinois River watershed, where land application of poultry litter is now limited.
Karst is formed when chemical weathering, such as acid rain, or natural dissolution breaks down limestone, dolostone marble or evaporite deposits — types of geological formations, according to the Encyclopedia of Arkansas.
Karst terrain can have caves, springs, “disappearing streams” and sinkholes, among other features. “Disappearing streams” are waters that disappear from the surface, travel underground through fractures and show up at a surface level elsewhere.
Karst is widespread in the Ozark Plateaus. A portion of southwest Arkansas has limestone and several springs and caves, and the Boston Mountains region in north Arkansas has limestone and numerous caves and springs.
The Arkansas Geological Survey describes karst-susceptible land as running across north Arkansas, from Washington and Crawford counties in the west to Randolph and Lawrence counties in the east.
In comments submitted to the Arkansas Department of Environmental Quality on its new draft of impaired water bodies list, Jessie Green, executive director of the White River Waterkeeper, said the phosphorus index should account for subsurface leaching. It said the fact that it doesn’t is “a considerable failing.”
But the index was developed as a way to analyze surface runoff risks, not subsurface risks, Sharpley said.
“That is not what this is designed to do,” he said.
C&H Hog Farms’ permit application did not account for karst, which the Department of Environmental Quality decided was ultimately needed, among other things, in order to issue the permit.
The Department of Environmental Quality did not grant an interview request — sought over the course of several weeks — for this article.
In its denial of C&H’s permit, the department noted excess phosphorus not absorbed by crops is “vulnerable to removal by surface runoff or leaching.” The statement of basis for permit denial also mentions the phosphorus index “may still allow application of swine waste because of other factors.”
After C&H’s permit was denied, Watkins said the index is “only as good as what’s factored into it.”
The index should better account for local conditions, Sharpley said. He and others are updating the index, which was written in 2010, to factor in row-crop conditions of east Arkansas.
“That will probably look quite a bit different than the index for pastures, I would guess,” Haggard said.
C&H Hog Farms’ permit application did not account for karst, which the Department of Environmental Quality decided was ultimately needed, among other things, in order to issue the permit.