Abstract

Preferential flow is a well recognized mechanism for the accelerated leaching of nutrients and pollutants through soil, contributing to the contamination of surface- and groundwater bodies. This study assessed the risks associated with slurry spreading and the potential effects of preferential flow, under natural rainfall, on four soil types with contrasting textures under wet and dry initial conditions. Breakthrough patterns of bromide were analyzed to quantify water flow patterns, and the data were compared to leachate nutrient composition. Bovine slurry, spiked with bromide, was applied to lysimeters (3 per treatment and 4 soil types) each under wet and dry initial soil conditions. Bromide served well as an indicator of the potential occurrence of preferential flow. Preferential flow was found to be most likely to occur in the soil with the finest texture under wet initial conditions and least likely in the soil with the coarsest texture. Leaching of relatively high concentrations of total reactive phosphorous was found to occur simultaneously with bromide under wet initial conditions, but no other relationships were observed between nutrients and bromide. Dye was applied to one lysimeter of each soil type at the end of the experiment to compare qualitative information about the infiltration mechanisms. Preferential flow was found to occur primarily in the form of macropore flow. Water quality considerations must be taken into account when promoting the spreading of organic manures on wet soils in early spring to improve nutrient efficiency. The land application of slurry at agronomic rates related to crop requirements restricts nutrient leaching.

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