Fig. 4. Mean annual NO^–₃–N loss in drainage discharge as influenced by cropping phase with and without a winter rye cover crop from 1999 to 2001 at Lamberton, MN. Error bars represent standard errors of the least-square means of treatments. Letters above the bars represent statistically significant groups. Treatments with the same letter are not different (t test, pairwise comparison, = 0.1).