LAND APPLICATION OF POULTRY LITTER AND WATER-QUALITY IN OKLAHOMA, USA

With the rapid growth of the poultry industry in Oklahoma, U.S.A., mor e litter is applied to farm land. Thus, information is required on the impact of applications on regional soil and water resources. The effe ct of soil and poultry litter management on nitrogen (N) and phosphoru s (P) loss in runoff and subsurface flow from four 16 m(2) plots (Rust on fine sandy loam, 6 to 8% slope) was investigated under natural rain fall. Plots under Bermudagrass (Cynodon dactylon) received 11 Mg litte r ha(-1), which amounts to contributions of approximately 410 kg N and 140 kg P ha(-1) yr(-1). In spring, litter was broadcast on 3 of the p lots; the upper half of one and total area of the other two. One of th e total-area broadcast plots was tilled to 6 cm, the other remained as no till. The fourth plot served as a control. Relative to the control , litter application increased mean concentrations of total N and tota l P in runoff during the 16-week study for no-till (15.4 and 5.8 mg L( -1)) and tilled treatments (16.7 and 6.1 mg L(-1)). However, values fo r the half-area application (5.6 and 2.0 mg L(-1)) were similar to the control (5.7 and 1.3 mg L(-1)). Interflow (subsurface lateral flow at 70 cm depth) P was not affected by litter application; however, nitra te-N concentrations increased from 0.6 (control) to 2.9 mg L(-1) (no t ill). In all cases, < 2% litter N and P was lost in runoff and interfl ow, maintaining acceptable water quality concentrations. Although litt er increased grass yield (8518 kg ha(-1)) compared to the control (350 1 kg ha(-1)), yields were not affected by litter management. An 8-fold increase in the plant available P content of surface soil indicates l ong-term litter management and application rates will be critical to t he environmentally sound use of this nutrient resource.