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Disposal of Feedlot-Lagoon Water by Irrigating Bromegrass: II. Soil Accumulation and Leaching of Nitrogen¹

ABSTRACT

This field experiment measured the role of soil accumulation and leaching of N when bromegrass (Bromus inermis) was irrigated with beef-feedlot-lagoon water. The 4-year study included three replications at irrigation rates of 0, 2.5, 5.1, 7.6, and 10.2 cm irrigation^–1. The heaviest irrigation added 1,890 kg N ha^– during the 4 years. Microplots encased in steel pipes in the main plots received 5.1- and 10.2-cm irrigations with lagoon water enriched with (¹⁵NH₄)₂SO₄.

With the main plots, there were no significant differences in total or inorganic soil N due to treatments. Profile contents of total N in the microplots increased during the experiment with 10.2-cm irrigations, and decreased with 5.1 cm. Amounts of leaching were small and were related to drainage from the profile rather than quantities of N added. Leaching did not constitute a significant hazard to underground water supplies.

The linear relationship between amounts of labeled NH₄⁺-N added and labeled N found in the soil to 70 cm deep was highly significant. Most of the labeled N was in the 0- to 10-cm soil layer with 88–94% of it immobilized in organic forms. The N balance after 4 years for the 5.1-cm treatment showed 28% of the labeled N applied as NH₄⁺ was in the soil profile, 41% used by the crop, 31% lost as a gas, and 0.7% leached below 105 cm. With the 10.2-cm treatment, 20% was in the soil, 38% used by the crop, 40% lost as gas, and 1.3% leached.

Key Words: water pollution • leaching • nitrogen-15 • isotopes • denitrification • immobilization

¹ Contribution no. 81-466-j, Department of Agronomy, Kansas Agric. Exp. Stn., Manhattan, KS 66506.

² Professor, Graduate Research Assistant, former Professor, Associate Professor, and Professor, respectively. Dr. Powers is now Director, Water Resources Center, University of Nebraska, Lincoln, NE.

Received for publication June 30, 1981.