Alfalfa Cuts Down Nitrogen Loss
Written by Dan Wiersma and Ev Thomas*
|Hold on to Nitrogen||Alfalfa Does the Job||Good Stewards of the Land|
A battle is in motion between farmers in three Iowa counties and the city of Des Moines. The Des Moines Water Works 2015 federal lawsuit is attempting to hold farmers responsible for the high nitrate levels found in the Raccoon River, the source of drinking water for this urban community.
Sensitivity to environmental issues among the public has pushed the agricultural community to become more proactive in telling its land stewardship stories. One of the most problematic environmental concerns surrounds nitrogen in our water systems. Nitrogen is a building block of living organisms and is the most abundant nutrient used by growing plants.
One of the challenges with nitrogen is its mobility in soil and water when converted to its nitrate (N03) form. The USEPA (United States Environmental Protection Agency) has established a 10 ppm nitrate-N standard for groundwater due to the human health issues associated with high nitrate levels in drinking water. Future standards are likely for surface water, including subsurface drainage systems that drain directly into streams and rivers. For example, the USEPA has an initiative to reduce nitrates by 45 percent in the Mississippi River through changes in farming practices among other things.
Hold on to Nitrogen
Management of nitrogen movement in cropping and livestock systems will be vital going forward. A critical question is whether nutrient practices will be a continuation of the voluntary stewardship efforts of farmers, or implementation of government-mandated practices. Recent efforts have focused on the adoption of best management practices for nitrogen fertilization. Many states provide guidelines for efficient use of N fertilizers that help maximize both profit and minimize environmental impact.
Cropping systems that include a perennial crop (like alfalfa) or some type of cover crop hold potential for helping minimize potential N losses from the crop landscape. Cover crops planted after harvest can protect soil from moving and can absorb soil nutrients for remobilization during the next growing season.
Perennial crops like alfalfa can protect soil from moving and can absorb nutrients like nitrogen, helping protect water quality.
Alfalfa Does the Job
So, where does alfalfa fit in this discussion? Alfalfa is a long-lived perennial crop species that maintains a living root system all year. Alfalfa biologically fixes atmospheric nitrogen but will utilize available nitrate-N from the soil first and is effective at scouring N from soils. It is deep rooted, growing to depths of 15 to 20 feet. Unlike annual crops, alfalfa captures nitrate-N from deep in the soil profile. It can remove 250 pounds per acre or more nitrate-N per year with good growing conditions.
Alfalfa reduces nitrate-N loss compared to corn and soybean systems. In a Colorado South Platte Valley cropping system study, alfalfa fields had the lowest nitrate-N levels. At the University of Minnesota, Gyles Randall documented 35 times lower nitrate-N concentrations from drainage tile under alfalfa fields versus corn and soybean fields. Michael Russelle (USDA-ARS) showed that planting alfalfa above tile drains and in buffer strips can keep excess nutrients from moving into waterways.
Alfalfa is popular on dairy and beef farms where forages are important for animal production. Alfalfa planted in rotation with corn maximizes the use of manure nutrients and legume N credits. However, alfalfa acres on dairy and beef farms have declined and have been replaced with corn. Based on research, one of the real costs of this shift in cropping systems will likely be higher nitrate-N leakage. In addition, erosion of soil and its quality may decline as acres shift from perennial to annual crop species.
Good Stewards of the Land
As we’ve discovered, incorporating more alfalfa into crop rotations has the greatest potential to reduce nitrate-N movement compared to other management practices. For grain farms where alfalfa is not part of the crop rotation, alfalfa may play a different role. One alternative is to plant alfalfa in field and landscape buffer zones adjacent to cropland. This serves to help slow groundwater movement and to filter out fertilizers or capture eroded soil prior to getting into ground or surface waters.
Some of these strategies may require economic incentives to drive adoption. Most landowners recognize the benefits of being good stewards of the land and soil they make their living on. They see more biodiversity and wildlife along with less soil erosion and cleaner streams when they plant fields or buffer strips to alfalfa. In spite of this, farmers are under mounting scrutiny by their neighbors, even though they may be several counties away as is the case in the Raccoon River Valley watershed of Iowa.
Alfalfa stands alone in having a great history of protecting and enhancing nearly 20 million acres of U.S. farmland. Alfalfa is a deep-rooted plant species helping us protect water quality by reducing runoff and by limiting nitrate-N leaching to groundwater.
In addition, alfalfa improves soil quality, sequesters carbon, and breaks disease and pest cycles in cropping systems. What is the future alfalfa story for your farm?
*Dan Wiersma is the alfalfa business manager with DuPont Pioneer. Ev Thomas is retired from the William H. Miner Agricultural Research Institute and president of Oak Point Agronomics Ltd.
Used by permission from the October 10, 2016, issue of Hoard’s Dairyman. Copyright 2016 by W.D. Hoard & Sons Company, Fort Atkinson, Wisconsin.