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Disposal of Feedlot Lagoon Water by Irrigating Bromegrass: I. Crop Removal of Nitrogen¹

ABSTRACT

Beef-feedlot lagoon water was used to irrigate bromegrass (Bromus inermis) at four rates in three replications for 4 years to determine effectiveness of the grass in removing N. Microplots within the main plots of two treatments received lagoon water enriched with ¹⁵N. Bromegrass was harvested two or three times each year. Yields and total N uptake were determined for the main plots, and yields, total N uptake, and lagoon water N uptake for microplots.

Yields and total N uptake increased with lagoon water rates, but declined with time on the main plots because of effects of excessive moisture on stands. In the microplots, reseeded to maintain stands, yields increased with time. With both main plots and microplots, more total N was removed by the hay than was applied with the 2.5- and 5.1-cm treatments, but the opposite prevailed for 7.6- and 10.2-cm irrigations.

Uptake of lagoon water N was 1.8 times more for the 10.2- than for the 5.1-cm treatment. The percentage of lagoon water N removed increased with time but seemed to be leveling off at about 40 after 4 years.

Crop removal of N in waste water can be a major N disposal method if crop yields are high. Bromegrass is not the best crop because stands are reduced by excessive moisture. Low rates of lagoon water are more effective than high rates because they leave less lagoon water N in the soil and more total N is taken up than applied.

Key Words: pollution • ¹⁵N • isotopes

¹ Contribution 81-444-J, Department of Agronomy, Kansas Agric. Exp. Stn., Manhattan, KS 66506.

² Professor, Graduate Research Assistant, former Professor, and Associate Professor, Dep. of Agronomy, Kansas Agric. Exp. Stn. Dr. Powers is now Director, Water Resources Center, University of Nebraska, Lincoln, NE 68583.

Received for publication May 26, 1981.