Drainage Contractor

Explaining edge-of-field practices in Iowa

September 20, 2019
By Shane Wulf

Shane Wulf, edge-of-field coordinator with the Iowa Department of Agriculture and Land Stewardship, wrote about the various kinds of edge-of-field practices available in Iowa for the Iowa Land Improvement Contractor’s latest newsletter. 

Context – why do edge-of-field practices matter?

The Iowa Nutrient Reduction Strategy (NRS) directs efforts to reduce nutrients in surface water from both point and non-point sources in a scientific, reasonable, and cost-effective manner. The Strategy was prompted in an effort to reduce nutrient loads that are transported to the Gulf of Mexico. The plan established a goal of 45 percent reduction of total nitrogen and total phosphorus loads.

The three primary groups of conservation practices related to agriculture include management practices, land use-practices and edge-of-field practices. Significant increases in adoption of all three groups of these practices will be necessary to achieve the 45 percent reduction of total nitrogen and phosphorus loads.

Edge-of-field practices

The edge-of-field practice category includes several practices that were developed to manage drainage water in a manner which effectively reduces nutrients such as wetlands, buffers and filter strips. These practices also include two recently developed, yet well researched projects that involve intercepting tile outlets and diverting water to carbon sources for the purpose of denitrification.

The first practice is a saturated buffer. Field tile drainage is intercepted in a riparian buffer or filter strip and a fraction of the flow is diverted as shallow groundwater within the buffer. The nitrate-N contained in the tile drainage water is partially removed by plant uptake, microbial immobilization and denitrification. Typical costs for a saturated buffer range from $2,500 to $5,000.

The second practice is called a woodchip denitrifying bioreactor. It works very similarly to a saturated buffer, however, the water is diverted into a pit of woodchips rather than along an existing filter strip. These pits average 20 feet wide, 80 feet long and approximately four feet in depth. Average costs for a bioreactor range from $10,000 to $15,000.

Both of these practices are efficient at reducing nitrogen, require small foot-prints and have no impact on existing cash-crops. There is also the added benefit that these can be constructed during those generally slow summer months. It is also certainly worth considering adding these practices (where feasible) to new drainage systems. Specifications, however, do not allow these projects to be installed where surface inlets are present.

Wetlands are another structural-based conservation practice option, which has numerous verified benefits including denitrification and improved wildlife habitat. Wetlands, specifically designed to reduce nitrogen loading to Iowa’s waterways, will play a major role in our efforts towards Iowa Nutrient Reduction Strategy goals. Wetlands are capable of treating thousands of acres of surface and subsurface drainage and average a 52 percent reduction in Nitrate-N.

Cost sharing

The Iowa Water Quality Initiative is a funding mechanism to assist producers and landowners in implementing priority practices like bioreactors, saturated buffers, and wetlands. This program has the ability to cost-share up to 75 percent on saturated buffers and bioreactors when used on its own and up to 100 percent when used in conjunction with federal or private funding.

There are several programs available to financially support the installation of wetlands and in some cases establish conservation easements. Those interested can contact Shane Wulf to learn more about these cost-share opportunities.