Nutrient reduction science assessment to provide roadmap for farmers
By Jean Caspers-Simmet
Date Modified: 10/03/2012 10:11 AM
DES MOINES —Iowa researchers are completing a nutrient reduction science assessment that will guide efforts to reduce nitrogen and phosphorus that are getting into the Mississippi River and contributing to Gulf of Mexico hypoxia.
Dean Lemke, natural resources engineer with the Iowa Department of Agriculture and Land Stewardship, and Matt Helmers, an agricultural and biosystems engineering professor at Iowa State University, provided an overview of the nearly completed assessment at the recent Mississippi River Gulf of Mexico Watershed Nutrient Task Force meeting in Des Moines.
The assessment tool involved researchers from IDALS, ISU, the Department of Natural Resources, the University of Illinois, the University of Minnesota, USDA's Agricultural Research Service and the EPA.
"We strongly felt that the initial step was to improve our science and technical understanding of addressing non-point source nutrient transport in food and agricultural production areas," Lemke said. "In Iowa, food production dominates our landscape and its impact on water quality is something that fits across our entire 36 million acres."
The state hasn't had a good technical understanding of how to address non-point source landscapes at full landscape scale to achieve significant reductions, Lemke said.
IDALS partnered with ISU's College of Agriculture and Life Sciences, which sponsored the 27-member team that met every two weeks for the past two years.
"The assessment is nearing completion with the cost information still to be completed," Lemke said. "The outcome far exceeds our initial expectation and gives us a science road map we haven't had before."
The rationale driving the project was the need to address nutrient loading to the Gulf of Mexico. As states define strategies to make reductions, performance of practices needed to be summarized for Iowa conditions, Helmers said. An estimated level of implementation and a cost needed to be developed.
Researchers established a baseline of existing conditions, Helmers said. Researchers estimated the potential load reductions of implementing nutrient reduction practices, and estimated the cost of implementation and the cost per pound of nitrogen and phosphorus reduction.
Researchers listed practices that would have the greatest potential for nitrogen and phosphorus reduction, Helmers said. Cost of practices was considered, realizing some practices have recurring costs and some have an upfront capital cost.
To reduce nitrogen loading in the field, cover crops, reducing nitrogen application, sidedressing spring applied nitrogen, using a nitrification inhibitor with fall applied fertilizer and moving all anhydrous application to spring were considered.
Edge-of-field practices include installing wetlands to treat 45 percent of agricultural acres, installing denitrification bioreactors, buffers and controlled drainage. Planting perennial energy crops, pasture and land retirement and doubling the amount of extended rotation acreage are land use changes being considered.
Rate reduction on soils that test high or very high for phosphorus, no-till or reduced tillage, and planting cover crops are practices for reducing phosphorus loading. Land retirement, pasture and buffers are other practices.
Getting to the Hypoxia Task Force target of 41 percent non-point source load reduction for nitrogen and 29 percent for phosphorus will take a combination of practices, Helmers said.
"Knowing the starting point is still a challenge and knowing what is being done on the land could improve estimates of progress that can be made," Helmers said.