Measuring Urea Persistence, Distribution and Transport On Coastal Plain Soils.

KEYWORDS: Urea, Poultry litter, Surface runoff, Leachate, Domoic acid, Chesapeake Bay

ABSTRACT

The persistence and mobility of urea, an organic form of nitrogen present in animal manures and commercial fertilizers, has rarely been studied and measured, because it is assumed to undergo rapid hydrolysis to ammonia. However, preliminary studies have shown urea to exist in leachate and runoff several days after manure applications. Our hypothesis is that urea in soils amended with manures, poultry litter and commercial urea fertilizers can persist long enough to be transported to surface waters. Urea in small concentrations can trigger the diatom Pseudo-nitzschia spp. to produce domoic acid (causative agent for amnesic shellfish poisoning), which is of concern in the Chesapeake Bay. A poultry litter and commercial urea fertilizer incubation experiment was conducted on Othello soil to characterize urea persistence. This study used several methods to assess runoff and leaching as hydrological pathways for urea to enter water bodies. A runoff experiment was performed using packed soil boxes and rainfall simulation on Othello silt loam. The treatments included urea, poultry litter, layer manure and a control. The vertical distribution of urea in soil cores taken from plots amended a few days prior to a rainfall event was determined. Three leaching experiments were conducted using different soils. Experiment 1 employed the use of piezometers on a Quindocqua silt loam; experiment 2 used buried lysimeters placed 30 cm beneath Quindocqua silt loam, and experiment 3 employed intact soil columns collected from three different soils:  the Bojac, Evesboro, and Sassafras series. Additionally, we characterized urea concentrations in channels and drainage ditches throughout the Manokin River watershed during base flow and storm events. Quantitative information on the effects of fertilizer forms and time after application on the amounts of urea found in runoff and leachate will be used to identify practices that have the potential to minimize urea losses to surface and ground water.