Clearing the Waters
U of A scientists develop phosphorus index to help resolve dispute over water quality
June 14, 2006Contact Information:
Dr. Tommy Daniel, Professor of Crop, Soil and Environmental Sciences
479-575-5720 / tdaniel@uark.edu
Dr. Brian Haggard, Associate Professor of Biological and Agricultural Engineering
479-575-2879 / haggard@uark.edu
Dr. Paul De Laune, Post Doctoral Associate
479-575-7585 / pdelaun@uark.edu
Dr. Indrajeet Chaubey, Associate Professor of Biological and Agricultural Engineering
479-575-4929 / chaubey@uark.edu
University of Arkansas scientists Tommy Daniel, left, and Paul DeLaune collect water samples from a watershed test field in a project to develop a phosphorus index for the Eucha-Spavinaw watershed in northwest Arkansas.
University of Arkansas scientist Brian Haggard helped chart water flow and runoff in a project to develop a phosphorus index for the Eucha-Spavinaw watershed in northwest Arkansas.
FAYETTEVILLE, Ark. — University of Arkansas Division of Agriculture scientists have developed a court-approved phosphorus index for the Eucha/Spavinaw watershed that helps resolve a dispute between Arkansas and Oklahoma.
The new index sets a standard by which nutrient management plans can be written for poultry and cattle operations within the watershed, a 415-square-mile drainage basin in northeast Oklahoma and northwest Arkansas, said Paul DeLaune, a post doctoral research associate.
DeLaune worked with Division of Agriculture soil scientist Tommy Daniel and biological and ecological engineers Brian Haggard and Indrajeet Chaubey to develop the Eucha-Spavinaw phosphorus index (ESPI).
The project is court-mandated in response to a lawsuit by the city of Tulsa and its water authority against six Arkansas poultry companies. The suit concerns the impact on water quality in the Eucha-Spavinaw watershed as a result of nutrient runoff from Benton County pastures fertilized by poultry litter, said Dr. Mark Cochran, co-chair of the division’s Environmental Task Force and head of the department of agricultural economics and agribusiness.
The issue revolves around the phosphorus content of poultry litter, DeLaune said. Phosphorus is a valuable nutrient for pasture grasses. But when it runs off with rainwater into streams and lakes, it can cause algae blooms — explosive growth of algae that affects water quality in reservoirs like Lake Eucha, which provides drinking water for Tulsa.
In accordance with a court settlement, the U of A and Oklahoma State University each developed phosphorus indexes for Eucha-Spavinaw and submitted them to the judge, who selected the U of A index for trial implementation.
Arkansas has an existing phosphorus index, developed by the Division of Agriculture, but the court settlement required a phosphorus index that was more restrictive for land application of poultry litter within Eucha-Spavinaw, DeLaune said.
ESPI requires annual soil tests. “We’re looking for soil test P,” Daniel said. “That is, the phosphorus in the soil that is available as a nutrient for plants. This includes water soluble phosphorus, which is susceptible to running off in rainwater.”
Daniel said ESPI is a risk-based index that uses soil test P, geographic features and movement of waterborne nutrients through the soil to determine the potential for phosphorus runoff. Haggard and colleague Indrajeet Chaubet charted stream flow and surface runoff for Spavinaw Creek to determine how much water flowed through the watershed during each month.
“Those months with lowest amount of surface runoff, typically July through October, have the lowest risk of phosphorus runoff, and that affects application timing,” Haggard said.
There are four levels of risk in the index, from low potential to very high potential. Poultry litter cannot be applied to fields with a high or very high risk of runoff, Daniel said.
Litter applications can be made to low or medium risk fields within the watershed only with a nutrient management plan, DeLaune said. Management plans for Eucha-Spavinaw, based on the new index, began to be written in 2004. The plans specify how much litter can be applied, and where, how and when it can be applied.
The court appointed a special master to oversee implementation of nutrient management in the watershed, Daniel said. A four-person court-appointed nutrient management team, paid for by the poultry companies named in the lawsuit, works for the special master.
Because the amount of phosphorus in any source of poultry litter can vary, depending on the management practices of the poultry grower, a test to determine the phosphorus content is recommended, DeLaune said.
Daniel anticipates that similar phosphorus indexes, customized to specific areas, may have to be developed for the Illinois River or other watersheds. In the meantime, he said research continues to add data to the study to verify the effectiveness of the Eucha-Spavinaw phosphorus index and make adjustments as needed.