Spring 2008

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Safe, “swimmable-fishable” water is the goal

James Baker is a University Professor Emeritus in Agricultural and Biosystems Engineering.

Establishing a common goal is the first step to building consensus. In the case of Iowa’s water quality, that common goal is easy. Iowans want safe-to-drink, “swimmable-fishable” water.

Iowa State University has been, and continues to be, a leader in water quality research and demonstration with respect to agriculture in the Corn Belt since the late 1960s.

An early example of substantial federal funding for ISU water quality research was a five-year study (1976-80) of field-to-stream transport of sediment, nutrients and pesticides in the Four Mile Creek watershed in Tama County. The research, led by faculty in agricultural and biosystems engineering, agronomy and sociology, was funded by the U.S. Environmental Protection Agency and later by the USDA.

The basic information on hydrology and chemical fate and transport gathered from this and multiple companion projects in the intervening years set the stage for more federally funded research and demonstration projects, as well as projects funded by the Leopold Center for Sustainable Agriculture, the Iowa Water Center, Iowa state agencies and industry and commodity groups.

The research quantified nutrient losses associated with crop production and the use of fertilizers and manures. We’ve learned systems that affect land use and drainage, hydrology of the land, management practices and weather play dominant roles in the transport of nonpoint pollutants in general, and different forms of nutrients in particular.

Drainage from agricultural lands dominates water flow in most parts of the Corn Belt because agriculture occupies a major portion of the land area. In flatter, tile-drained landscapes, nitrogen losses, dominated by nitrate-nitrogen leaching, are of most concern and usually occur with sustained subsurface flows in spring and fall at times of little row-crop water use and nutrient uptake.

In contrast, in rolling landscapes with good surface drainage, phosphorus losses with runoff water and sediment are of more concern. These occur with rainfall-runoff events that can happen year-round, but are generally greater in spring when the soil has less cover.

The most important natural factors affecting nutrient losses are soil properties and weather. The Corn Belt is fortunate to have fertile soils and generally ample precipitation, but both lead to nutrient losses.

Information on management practices and systems garnered from Iowa State studies has been used to assess options available to reduce agricultural nutrient losses to water resources in the Corn Belt. Yet the number of acceptable tools is limited, must be targeted to site-specific conditions to be effective and come with significant costs.

For nitrogen losses the most important management factor is land use. The conversion to row crops with installation of artificial subsurface drainage where needed has created a productive system, but also has increased the potential for nitrate-nitrogen loss.

For phosphorus, land use in conjunction with tillage is generally the most important management factor affecting hydrology and erosion potential, and thus phosphorus loss. The combination of rate, method and timing of nutrient additions also affect loss, but generally is of lesser importance. Weather patterns often have more affect on nutrient losses than nutrient management.

Because inorganic forms of nitrogen and phosphorus must be present in the soil at concentrations sufficient for crop production, whenever excess water moves over or through the soil, nutrient losses will occur. Controlling these losses by a prescribed amount is extremely difficult.

In terms of a viable vision for future water quality improvements, there are no easy answers and improvements will be incremental.

But please know this — returning the Corn Belt to pre-settlement conditions is neither socially nor economically feasible, nor in the best interest of maintaining our nation’s food, feed and fuel production infrastructure.

The potential and limitations of in-field and off-site management practices and systems need to be considered relative to their costs and acceptance for implementation. Off-site management systems that include structural practices need to be implemented at a large number of sites to achieve landscape-level environmental improvement. Constructed wetlands are a vital part of these systems, and regulatory frameworks need to be compatible with this practice and scale of implementation.

Science indicates current nutrient impairment problems are not due mainly to mismanagement of fertilizers and manures, although certainly some improvement in management can and should be made. Overall, the majority of our nutrient impairments are due more to historic changes in land use and hydrology that came with the conversion of prairie and wetlands to productive cropland, using artificial subsurface drainage where needed.

Given this perspective, and that these historic changes have created a very productive system critical to our country’s food security, new, broader approaches to solving water quality problems are needed.

That’s why the work continues. Between 2002 and 2007, researchers at Iowa State University received external grants totaling more than $11.6 million for projects on water quality, watersheds and related activities. More than 60 water quality research and demonstration projects are underway.

Further research is needed to design and refine new management practices and develop cropping system alternatives, possibly with more sod-based rotations. This research and new information is even more critical in these times of change with respect to food and energy issues, and use and protection of our natural resources. However, any new approaches must be sustainable with respect to both soil and water quality, must be economically feasible and must be science-based.

James Baker (’71 Ph.D. physical chemistry) is a University Professor Emeritus in Agricultural and Biosystems Engineering.

“Systems that affect land use and drainage, hydrology of the land, management practices and weather play dominant roles in the transport of nonpoint pollutants.”

“Any new approaches must be sustainable with respect to both soil and water quality, must be economically feasible and must be science-based.”