Space restrictions prevented this letter from being published in the print edition of this week’s Observer.
Iowa has been working for decades to protect and improve water quality. However, progress measured toward reduction targets at the watershed scale has been challenging, and many complex nutrient-related impacts in Iowa’s lakes, reservoirs, and streams remain to be addressed.
The strategy related to farmland is built on a scientific assessment of practices and associated costs to reduce loading of nitrogen (N) and phosphorus (P) to Iowa surface waters. The College of Agriculture and Life Sciences at Iowa State University and the Iowa Department of Agriculture and Land Stewardship partnered to conduct the scientific assessment. The assessment shows that broad implementation of a combination of practices, will be needed to reach desired load reductions.
The need to increase voluntary efforts to reduce nutrient loss is one of the key points related to agriculture in Iowa’s Nutrient Reduction Strategy. The science assessment identified effective nutrient reduction practices in three categories — nitrogen and phosphorus management, land use, and edge-of-field. Management practices involve application rate, timing, and method, plus the use of cover crops and reduced tillage. Land use practices include perennial energy crops, extended rotations, grazed pastures, and land retirement. Edge-of-field practices involve drainage water management, wetlands, bioreactors, buffers, terraces, and sediment control. Practices that have the greatest potential are listed below.
Rate Reduction: Matching N application rates with the Corn Nitrogen Rate Calculator, a university developed online tool, has potential to reduce nitrate-N loss. This tool estimates optimal N rates based on fertilizer and corn prices.
Nitrification Inhibitor: Research shows a corn yield increase plus a nitrate-N loss decrease when using a nitrification inhibitor (Nitrapyrin) with fall applied anhydrous ammonia.
Sidedress: Sidedressing N can be done in different ways and with different sources of N, yet the concept of applying fertilizer after corn emergence is consistent. This strategy includes applying N during plant uptake, as well as timing to reduce the risk of loss from leaching events.
Management Practices – Phosphorus
Cover Crops: Planting a late summer or early fall seeded cover crop can reduce P loss. For example, winter rye offers benefits of easy establishment, seeding aerially or by drilling, growth in cool conditions, initial growth when planted in the fall, and continued growth in the spring. Cover crops also are effective at reducing N loss.
Reduced Tillage: Conservation tillage, where 30% or more of the soil surface is covered with crop residue after planting, or no-till, where 70% or more of the soil surface is covered with crop residue after planting, reduces soil erosion and surface runoff. Reduced erosion and runoff also reduces P transport.
Land Use Practices –Nitrogen and Phosphorus
Extended Rotations: Extended rotations reduce the application and the loss of both P and nitrate-N. If a shift to extended rotations is significant, the amount of corn and soybean produced in Iowa would be reduced, along with an increase in alfalfa production that could support increased livestock production for alfalfa feeding. Another benefit would be improved soil quality.
Edge-of-Field Practices – Nitrogen and Phosphorus
Wetlands: Wetlands targeted for water quality benefits show great potential for nitrate-N reduction. Wetland costs include design, construction, buffer seeding, maintenance, and land acquisition.
Bioreactors: Subsurface drainage bioreactors also show good potential for nitrate-N reduction. Bioreactor costs include control structures, woodchips, design, construction, seeding, additional tile, management, and maintenance.
Buffers: Edge-of-field technologies such as buffers are designed to settle sediment and sediment-bound N and P, along with retaining nitrate-N and dissolved P. Buffers also provide wildlife habitat, sequester carbon, reduce greenhouse gas emissions, stabilize stream banks, and potentially reduce flood impacts.
Saturated Buffers: Field tile drainage is intercepted in a riparian buffer and a fraction of the flow is diverted as shallow groundwater within the buffer.
Iowa’s Nutrient Reduction Strategy is a key step toward improving Iowa’s water quality while ensuring the state’s continued economic growth and prosperity. The Practices List will evolve over time as new information, data, and science are discovered and adopted.
The path forward to reducing nutrient impacts will not be easy, as it will require a high adoption rate of multiple practices to achieve the goal of cleaner water and a profitable agriculture.
To learn more about the practices that may be right for your farm, attend a field day, contact the Iowa Department of Agriculture and Land Stewardship, Iowa State University Extension and Outreach, or a certified crop advisor.
Kyler Oswald, President
Carroll County Farm Bureau – President
Coon Rapids, IA