POULTRY LITTER-TREATED LENGTH EFFECTS ON QUALITY OF RUNOFF FROM FESCUE PLOTS

Using experimental data and/or mathematical simulation models to ident ify practices that reduce pollution from manure-treated areas is somet imes perceived as limited by the unknown validity of extrapolating plo t-scale data to larger areas and by uncertainties in modeling transpor t of various pollutants. The objectives of this study were to assess t he effect of length of manure treatment on runoff concentrations of po ultry litter constituents and to define the modes of transport (partic ulate versus soluble) for nitrogen (N), phosphorus (P), carbon (C), an d solids. Poultry litter was applied to three 1.5- x 18.3-m fescue (Fe stuca arundinacea Schreb.) plots with runoff collection gutters instal led at 3.0-m intervals along the lengths of the plots. Runoff was gene rated from simulated rainfall (50 mm/h for 1 h of runoff), and samples were analyzed for total Kjeldahl N (TKN), organic N (Org-N), ammonia N (NH3-N), nitrate N (NO3-N), total P (TP), total organic C (TOC), and total suspended solids (TSS). Soluble fractions of TKN, Org-N, NH3-N, TP, and TOC were also determined. Manure-treated length had no effect on runoff concentration of any parameter indicating that a manure-tre ated length of only 3.0 m would have been sufficient to simulate runof f quality associated with longer manure length treatments. Proportions of TKN, Org-N, NH3-N, and TP transported in soluble form were high (g reater than or equal to 74%), and over half of the TOC in the runoff w as in soluble form. These results indicate that for conditions similar to those of this study, extrapolation with respect to runoff concentr ations might be possible with little adaptation of the data and might simplify, the design of management practices that key on edge-of-field runoff concentrations. The results with regard to modes of transport can help to better model losses of N, P, and COD and suggest that loss es of these parameters will be most effectively controlled through pra ctices that focus on reducing soluble losses rather than simply reduci ng erosion.