Local and field-scale nutrient loss pathways from fresh and composted broiler litter applied to hayfields

Composting broiler litter may lower the hazard of contaminating ground and surface water with nitrogen (N) and phosphorus (P) from excess applications. Prediction of nutrient transport through the vadose zone is complicated by the combination of soil structure and preferential flow, but quantification of the relationship has remained problematic. This project determined N and P field-scale losses from fresh and composted litter applied to hayfields and studied the relationship between subsoil structural development and preferential flow.; Two rates of broiler litter, 10(1X) and 20 Mg ha{dollar}{bsol}sp{lcub}-1{rcub}{dollar} year{dollar}{bsol}sp{lcub}-1{rcub}{dollar} (2X), and a mix of 10 Mg ha{dollar}{bsol}sp{lcub}-1{rcub}{dollar} year{dollar}{bsol}sp{lcub}-1{rcub}{dollar} of broiler litter and 50 Mg ha{dollar}{bsol}sp{lcub}-1{rcub}{dollar} year{dollar}{bsol}sp{lcub}-1{rcub}{dollar} of composted litter (1X + C), were split-applied for two years. Surface and subsurface flow were monitored for inorganic and total N and P. Experiments at local and field scale were used to study the relationships between structural development, saturated conductivities {dollar}(K{bsol}sb{lcub}s{rcub}),{dollar} water retention and breakthrough parameters, dye staining of flow paths and observations of preferential flow at the field scale.; Nitrate concentrations in subsurface flow remained under the U.S.E.P.A. drinking water standard for all treatments. Dissolved reactive P (DRP) concentrations in runoff reached a maximum of 8.5 mg L{dollar}{bsol}sp{lcub}-1{rcub}{dollar} under the 1X + C treatment. Average DRP concentrations were statistically higher under the 1X + C treatment, followed by the 2X and 1X treatments. Concentrations of resin extractable P (Pr) in soil increased sharply. Average DRP concentrations in runoff were correlated to total applied P indicating that this was the principal determinant of DRP concentrations in runoff. This relationship in combination with the curve number method was used successfully to predict cumulative DRP losses. Composting, although effective in controlling nitrate leaching, did not lower DRP concentrations in runoff.; Structure was indicated by high CV of {dollar}K{bsol}sb{lcub}s{rcub},{dollar} high dispersivity, low dyed area, low mobile water content and low exchange coefficients. Field-scale observations matched the differences in structure and parameters observed at the local-scale. Local-scale preferential flow appeared to highly influence field-scale solute transport, indicating that this is an important local-scale process. A conceptual model of subsoil structural development was expanded with physical parameters matching the structural development stage.