Land application of poultry manure and its influence on spectrofluorometric characteristics of dissolved organic matter

• Organic nutrients in manure runoff can contribute to eutrophication.
• Runoff DOM was evaluated for corn cropland receiving manure application at 9 Mg ha−1.
• Concentrations in runoff were highest after manure application but declined rapidly.
• Manure contributed labile, less aromatic and low molecular weight DOM.
• Wetter spring conditions and large storms can pose challenges for manure application.

Land application of manure is a common practice that is used to supplement nutrients from fertilizers as well as to reuse and recycle waste in agricultural watersheds. Excess application of manure can however result in elevated exports of organic and inorganic nutrients in runoff. We evaluated the concentration and composition of dissolved organic matter (DOM) in runoff from cropland (corn) receiving poultry manure. Manure was applied once every three years at the rate of 9 Mg ha−1 in early spring and was incorporated into the soil during application. Surface runoff and soil water sampling was performed for eight natural storm events with one storm event prior to manure application. Samples were collected from the field edge, upland and lowland riparian zones and a receiving stream. Concentrations of dissolved organic carbon (DOC) were highest at the field edge (mean: 94 mg L−1) and then declined sharply for the riparian and stream locations. Temporally, DOC concentrations in field runoff were highest for the first storm event following manure application and then declined quickly over the next 1–3 weeks. DOM composition in runoff following manure application had low aromaticity and a microbial/tryptophan-like character. These characteristics evolved with time toward more aromatic, more humic, and a terrestrial-like DOM composition. The decrease in runoff DOM was attributed to sorption and microbial degradation. Our observations suggest that while concentrations of DOM can be low in manure runoff, a short period (1–3 weeks) following manure application could be an environmentally sensitive and vulnerable period for runoff water quality.