With the rapid growth of swine (Sus scrofa domestica) production in the Oklahoma Panhandle, animal waste management has become a growing concern. Field experiments were conducted to evaluate the long-term eff ects of equivalent nitrogen rates of swine lagoon effl uent (SE), beef manure (BM), and commercial fertilizer on the yield and economic returns of irrigated corn (Zea mays L.) grown on calcareous Gruver silt loam soil (fi ne, mixed, superactive, mesic Aridic Paleustoll) near Goodwell, Oklahoma. A randomized, complete-block, split-plot design with three replications was used to test the main eff ects of N source (NS) and equivalent N application rates (NR) of 56, 168, and 504 kg N ha -1 . Both BM and SE generated signifi cantly (P < 0.05) higher corn yields than anhydrous ammonia (AA) across the main eff ect of NS. Greater separation of mean corn yields was found among NS as the equivalent NR rate was increased from 56 to 504 kg N ha -1 with the following rankings (P < 0.05): AA = BM = SE at 56 kg N ha -1 , BM = AA ≥ SE at 168 kg N ha -1 , and SE > BM > AA at 504 kg N ha -1 . Both SE and BM generated signifi cantly (P < 0.05) higher economic returns than AA. Th e highest ranked alternatives of economic returns were generated by SE×504 and BM×168. Results indicate that SE and BM can be economically viable substitutes for commercial fertilizer, bringing higher yields and economic benefi ts to producers in the Oklahoma Panhandle. ).Abbreviations: AA, anhydrous ammonia; BM, beef manure; IRR, applied irrigation; NR, equivalent nitrogen rates; NS, nitrogen source; N56, nitrogen applied at 56 kg N ha -1 ; N168, nitrogen applied at 168 kg N ha -1 ; N504, nitrogen applied at 504 kg N ha -1 ; SE, swine lagoon effl uent; YR, year.

This study estimates the farm-gate breakeven price of switchgrass relative to wheat in Oklahoma, USA. The breakeven price of switchgrass is determined for two situations: when external consequences are ignored and when the environmental costs of changes in soil erosion, fertilizer (nitrogen and phosphorous) runoff, and soil organic carbon (SOC) are considered. Results suggest that if indirect land use changes are ignored, the farm-gate breakeven price of switchgrass when only the internal costs are considered is 69% to 144% greater (depending on land quality) than if the value of selected external consequences are considered. The potential environmental benefits are greater if highly erodible land is switched from annual cropping to switchgrass.

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