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Effect of Feedlot Runoff on a Southern Illinois Forested Watershed¹

ABSTRACT

Beef (Bos taurus) feedlot runoff was applied to an oak-hickory (Quercus-Carya) forested watershed to evaluate the effectiveness of the forest in removing and utilizing the added nutrients. Application followed the normal precipitation pattern and was, thus, variable in intensity throughout the year. Feedlot effluent additions averaged 261.1 m³ ha^–1 over the 4-yr study period. High percentages of total nutrient additions were retained by the watershed, but drainage water quality declined over the study period. An average of 99.8% of the added K, 99.4% of the PO₄^–3-P, 99.2% of the Na, and 98.4% of the Ca and Mg were retained by the watershed. Nitrate-N was the only nutrient showing a net loss, averaging 276% of the added NO₃^–-N.

In the watershed runoff, NO₃^–-N increased from a baseline mean of 0.83 mg L^–1 to a treatment mean of 12.27 mg L^–1. Phosphate-P also increased from a baseline mean of 0.02 mg L^–1 to a treatment mean of 0.88 mg L^–1. Soil physical and chemical properties also changed as a result of the feedlot runoff input. Soil exchangeable cations and anions in the top 7.5 cm increased and bulk density decreased from 1.15 mg M^–3 to 1.03 mg M^–3. Maximum soil changes occurred within 30 m of the effluent discharge point.

Both tree and herbaceous plant species composition of the watershed also changed during the study period. Plant species composition became more similar to moist-site communities and plant numbers decreased overall. Species characteristic of dry sites decreased in growth rate, while moist site species increased in growth.

Results of the experiment indicate that (i) a gravity flow system is an efficient and economical means of dispersing feedlot runoff through a forested watershed, (ii) feedlot effluent can be utilized as a nutrient supplement, and (iii) the vegetation of the oak-hickory forest was an effective biological filter.

Key Words: gravity flow • water quality • nutrient loss • oak-hickory • maple-ash • livestock waste

¹ Supported in part by Illinois Agric. Exp. Stn. Hatch project 55-0344.

² Former research assistant, professor, and head of department and forester, respectively, Dep. of Forestry, Univ. of Illinois, Urbana, IL 61801.