Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2000
Publication Date: N/A
Interpretive Summary: Human activity has many effects on the environment, among which has been excessive nutrient loading in soils and water. Much of this nutrient loading comes from non-point sources, which are difficult to define, but occasional point sources occur, such as accidental spills during transport of fertilizer. For example, during 1998 in Minnesota, fertilizer spills occurred from 2 railroad accidents and 30 other transportation-related accidents. Some spills are relatively easy to clean up, but there is a need for low cost clean up techniques when other approaches fail. Nitrogen is one nutrient that can move from soil into water supplies and threaten human health. One way to clean up excess nitrogen is with crops, but legumes, like alfalfa, are usually overlooked because they do not need nitrogen fertilizer. In earlier research, we had discovered that alfalfa efficiently absorbs nitrogen from fertilizer and soil, so we worked with a railroad company and environmental consulting firm to clean up a railroad spill sit in North Dakota. We used the contaminated ground water for irrigation to 'fertilize' alfalfa with nitrogen. We found that alfalfa removed at least three times more nitrogen than corn or wheat crops. At the same time, a high value hay crop was produced. Our research showed that alfalfa provides an efficient way to clean up some sites contaminated by too much fertilizer nitrogen. In addition, this research showed that alfalfa should be very useful to clean up other sites that have too much nitrogen, such as fields where wastewater or sewage treatment effluent is applied. This new approach to preventing and cleaning nitrogen from ground water and soil will help protect public health and environmental quality.
Technical Abstract: An innovative plant-based environmental restoration program was developed at the site of a 1989 fertilizer spill. Standard remediation techniques had reduced the concentration of nitrate-N in local ground water, but nitrate-N concentrations in part of the site still exceeded the public drinking water standard in 1996. Our objective was to improve local soil and ground water quality by utilizing inorganic N in the ground water to produce a high value agricultural crop. A 3-year study was conducted in replicated plots (24 by 30 m) located hydrologically upgradient of the ground water under the spill site. In the spring of 1996, three alfalfa (Medicago sativa L.) entries [('Agate', Ineffective Agate (a non-N2-fixing elite germplasm similar to Agate), and MWNC-4 (a less dormant experimental germplasm with multiple pest resistance and higher productivity than Agate)] were seeded. Corn (Zea mays L.) or wheat (Triticum aestivum L.) was seeded adjacent to the alfalfa each year. Crops were irrigated with N-impacted ground water t meet water demand. During the 3-year period, an estimated 540 kg of inorganic N was removed from the aquifer through irrigation of 4.9 million L water. Cumulative N removal from the site over 3 years was 972 kg N/ha in Ineffective Agate alfalfa hay and was 287 kg N/ha for the annual cereal grain. Alfalfa reduced soil solution nitrate concentrations to low and stable levels, whereas they were more variable under the annual crops. Ground water quality improved over the course of the experiment, as evidenced by irrigation water N concentration. We do not know how much N was removed by the N2-fixing alfalfas, but it appears that either fixing or nonfixing alfalfa will perform well in removing inorganic N from N-impacted sites.