| Producers in regions with intense broiler (Gallus gallus) production take advantage of the plant nutrients contained in broiler litter (BL) to enhance yields of forage grasses. However, application of BL to pasture lands in karst regions, like the Ozark Highlands, can potentially reduce water quality if BL-derived contaminants enter surface or groundwater via runoff or drainage. Additionally, BL applications stimulate carbon dioxide (CO2) release from the soil to the atmosphere and may contribute to global warming. The objectives of this study were to determine long-term trends in runoff and soil leachate water quality and to evaluate soil respiration under natural precipitation from a Captina silt-loam soil (fine-silty, siliceous, active, mesic Typic Fragiudult) with a history of BL amendments under forage management amended annually with BL at three application rates (0, 5.6, and 11.2 Mg BL ha-1). Runoff and leachate were collected for an 8-yr period and pH, electrical conductivity (EC), soluble plant nutrients (i.e., NO3-N, NH4-N, PO4-P, Ca, K, Mg, Na, and P), trace metals (i.e., As, Cd, Cr, Cu, Fe, Mn, Ni, Se, and Zn), and dissolved organic carbon were measured. Similarly, soil respiration, temperature, and moisture were measured periodically for a 3-yr period. Litter application increased (P < 0.01) average annual flow-weighted-mean (FWM) runoff Fe and leachate Na concentrations, while all other annual runoff and leachate concentrations and loads and 8-yr cumulative losses were unaffected ( P > 0.05) by BL rate. Eight-year cumulative runoff losses were < 1 % for all elements except Se, which ranged from 12 to 20 % of that applied in litter. Similarly, 8-year cumulative leaching losses of NH4-N, C, N, P, Mn, and Cu represented < 2%, while Se and Cd exceeded 100% of that applied in BL. Soil respiration varied (P < 0.01) with BL rate, sample date, and year. Litter increased respiration after application and again after rain events relative to the unamended control in all years. Multiple regression indicated that respiration could be predicted using soil temperature at the 2-cm depth (T2cm) and the product of T2cm and soil volumetric water content (R2 = 0.52; P < 0.01). Results indicate that pasturelands with a history of BL application may release BL-derived metals in runoff and drainage waters at concentrations harmful to health and that organic amendments, such as BL, can stimulate release of CO2 from soil to the atmosphere, potentially negatively affecting atmospheric greenhouse gas concentrations. |
