Identifying long-term preferential and matrix flow recharge at the field scale

Preferential recharge from agricultural production fields can lead to agrochemical contamination of groundwater due to short-circuiting of the soil matrix. This research determines the relative amounts of preferential and matrix flow recharge from a no-till agricultural production field. The conservative tracer potassium bromide was surface applied to a 0.37 ha bermed fieldplot at a rate of 900 kg ha(-1) as bromide. The site was instrumented to monitor precipitation and runoff from the bermed field plot. Three years after the bromide application, twenty-one 3.65 m continuous soil cores were collected from the bermed plot and analyzed for bromide. Based solely on the shape of the bromide profiles, most of the 21 soil cores showed no apparent preferential flow. However, up to 83% of the infiltrated bromide mass was absent from individual soil cores, presumably due to preferential flow. Using a mass balance approach, we estimated that 58% of the recharge was due to preferential flow and 42% was due to matrix flow.