In a Pennsylvania field study, Stout et al. measured NO3-N leaching loss from spring-, summer-, and fall-applied urine and summer-applied fecal beneath N-fertilized orchardgrass (Dactyls glomerata) using drainage lysimeters. Urine N concentration reflected the N content of the herbage in the pastures and was highest in the spring or fall. The leachate patterns were similar for all 3 years of the study. Leachate volumes were lower during the grazing season when evapotranspiration was the highest and increased in the fall as evapotranspiration decreased. The pattern of NO3-N losses averaged for the 3 years of the study were 1.17, 1.68, 22.0, 24.0, and 31.5 g m-2 for the control, feces, and spring-, summer-, and fall-applied urine, respectively. The authors caution if dairy farmers in this region continue to increase the utilization of management intensive grazing, the amount of N leached to the groundwater from beneath urine patches could become substantial unless mitigated by improved grazing management.
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