Poultry litter-treated length effects on quality of runoff from fescue plots

Using experimental data and/or mathematical simulation models to identify practices that reduce pollution from manure-treated areas is sometimes perceived as limited by the unknown validity of extrapolating plot-scale data to larger areas and by uncertainties in modeling transport of various pollutants. The objectives of this study were to assess the effect of length of manure treatment on runoff concentrations of poultry litter constituents and to define the modes of transport (particulate versus soluble) for nitrogen (N), phosphorus (P), carbon (C), and solids. Poultry litter was applied to three 1.5- x 18.3-m fescue (Festuca arundinacea Schreb.) plots with runoff collection gutters installed at 3.0-m intervals along the lengths of the plots. Runoff was generated 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-treated length of only 3.0 m would have been sufficient to simulate runoff quality associated with longer manure length treatments. Proportions of TKN, Org-N, NH3-N, and TP transported in soluble form were high (greater than or equal to 74%), and over half of the TOC in the runoff was in soluble form. These results indicate that for conditions similar to those of this study, extrapolation with respect to runoff concentrations 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 losses of these parameters will be most effectively controlled through practices that focus on reducing soluble losses rather than simply reducing erosion.