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Critics find the Arkansas Phosphorus Index to be inadequate

January 7, 2019

LITTLE ROCK, Ark. (AP) — The method used to gauge how much fertilizer Arkansas farmers can apply to their crops doesn’t factor the potential of manure leaching underground and leaves the state’s waterways inadequately protected, according to critics.

Farmers use the Arkansas Phosphorus Index to calculate the potential of phosphorous runoff during a rain storm and to determine where to disperse animal waste, the Arkansas Democrat-Gazette reported . The Arkansas Department of Environmental Quality noted that manure can be applied only on land deemed to have a “low” or “medium” risk of runoff.

Jessie Green, executive director of the White River Waterkeeper, submitted a comment on the agency’s impaired water bodies list maintaining the phosphorus index should account for subsurface leaching. She said the fact that it doesn’t is “a considerable failing.”

The phosphorous index assesses three things collectively: phosphorus source potential, transport probability, and best management practices. Each of the three aspects has its own factor that concludes its value.

Phosphorus source potential is based on soil tests and the phosphorous application rate. Transport probability determines how easily phosphorous might move, based on the slope of the land and other elements. Best management practices include ponds, fencing or buffers on the land. Soil samples assist with recalculating the land’s risk every year.

Critics contend the karst terrain around the Buffalo River is a prime example of the index inadequately accounting for all of the ways phosphorus creeps into waterways. Karst areas often feature cracks, fissures and sinkholes that allow substances to trickle down and move underground.

Brian Haggard, director of the Arkansas Water Resources Center at the University of Arkansas — Fayetteville, argued the variability of karst areas means karst shouldn’t be factored into the index. Haggard said that farmers can look for visible signs of karst and decide what needs to be written into their nutrient management plans.

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Information from: Arkansas Democrat-Gazette, http://www.arkansasonline.com

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