An array of 18 zero‐tension pan lysimeters installed 1.2 m below the soil surface in 1988 was used to examine NO 3 leaching in 1991 to 1995. The experiment was designed to study NO 3 losses from continuous, fertilized corn, alfalfa, and the first year of corn rotated from alfalfa as a function of crop type, applied N fertilizer rate and longer‐term weather variability. The flow‐weighted mean leachate NO 3 ‐N concentration from the 3‐yr alfalfa stand was 4 mg L −1 . Annual leachate NO 3 ‐N concentrations from continuous, fertilized corn and corn following alfalfa at the estimated Economically Optimum N (EON) rate averaged 15 mg L −1 . Annual flow‐weighted average NO 3 ‐N concentrations in leachate from post‐alfalfa corn receiving 50 and 100 kg N ha −1 , which were above the EON rate, were 18 and 24 mg L −1 , respectively. The masses of NO 3 ‐N leached from the root zone of continuous corn at the estimated EON rate were 81 and 55 kg ha −1 in 1991 to 1992 and 1994 to 1995, respectively. Nitrate‐N losses from alfalfa in 1991 to 1992 were 9 kg ha −1 . Nitrate concentrations in leachate from an alfalfa stand were one‐quarter to one‐fifth as high as from corn receiving the EON rate. This research provides evidence that including alfalfa in a rotation would result in a considerable reduction in the amount of NO 3 leaving a farm in leachate.
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Toth et al. (1998) studied this question.