Alfalfa rapidly remediates excess inorganic nitrogen at a fertilizer spillsite

By 1996, standard remediation techniques had significantly reduced the conc entration of nitrate nitrogen (NO3--N) in local ground water at the site of a 1989 anhydrous ammonia spill, but NO3--N concentrations in portions of t he site still exceeded the public drinking water standard. Our objective wa s to determine whether local soil and ground water quality could be improve d with alfalfa (Medicago sativa L.). A 3-yr study was conducted in replicat ed plots (24 by 30 m) located hydrologically upgradient of the ground water under the spill site, Three alfalfa entries ['Agate', Ineffective Agate (a non-N-2-fixing elite germplasm similar to Agate), and MWNC-4 (an experimen tal germplasm)] were seeded in the spring of 1996, Corn (Zea mays L,) or wh eat (Triticum aestivum L,) was seeded adjacent to the alfalfa each year. Cr ops were irrigated with N-containing ground water to meet water demand. Dur ing the 3-yr period, about 540 kg of inorganic N was removed from the aquif er through irrigation of 4.9 million L water. Cumulative N removal from the site over 3 yr was 972 kg N ha (1) in Ineffective Agate alfalfa hay, compa red with 287 kg N ha(-1) for the annual cereal grain. Soil solution NO3- co ncentrations were reduced to low and stable levels by alfalfa, but were mur e variable under the annual crops. Ground water quality improved, as eviden ced by irrigation water N concentration. We do not know how much N was remo ved by the N-2-fixing alfalfas, but it appears that either fixing or non-N- 2-fixing alfalfa will effectively remove inorganic N from N-affected sites.