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Precipitation Nitrogen Contribution Relative to Surface Runoff Discharges¹

ABSTRACT

Ammonia and nitrate concentrations in precipitation and surface runoff from two adjacent watersheds, fertilized at 168 and 448 kg N/ha, respectively, were studied to determine the relative contribution of precipitation N in relation to surface runoff N discharge. The data show that 69% of the N discharged by surface runoff from the sampled events could be accounted for by precipitation-originated N on the watershed fertilized at 168 kg N/ha, whereas 53% of the N discharged from the watershed fertilized at 448 kg N/ha could be attributed to N originating in the precipitation. However, the data indicate that, on an annual basis, the surface runoff N discharge accounts for only 20% of that in the total incoming precipitation. This difference can be accounted for by precipitation intensity or duration that did not cause runoff, absorption of NH₄-N by the soil material, or leaching of NO₃-N into the soil profile.

Key Words: ammonia • nitrate • water pollution

¹ Contribution from the North Central Region, ARS, USDA, and the Nebraska and Iowa Agr. Exp. Sta. Published with the approval of the Director as Paper No. 3683, Journal Series, Nebraska Agr. Exp. Sta., Lincoln.

² Soil Scientists, USDA, Lincoln, Nebraska, and Council Bluffs, Iowa, respectively.

Received for publication December 17, 1973.