Influence of Plant Uptake on the Performance of Bromide Tracer
Bromide has been used to study solute transport in unsaturated soils. However, no field studies have addressed the impact of plant uptake on the performance and reliability of Br as a tracer. Field experiments were conducted in a Russet Burbank potato (Solanum tuberosum L.) field on a Plainfield loamy sand soil (mixed, mesic Typic Upidsamment) at the Hancock Research Station in central Wisconsin. At emergence, a 6.8-mm pulse of KBr solution with 15 kg m−3 concentration was banded at the center of each potato row. The application rate was equivalent to 111.2 kg ha−1 of Br. At 65 d after Br application, soil, potato canopies, tubers, and residues of dead potato leaves and vines from four vertical profiles were collected and the total mass of Br from each sample was measured. The results showed that at least 53% of applied Br mass was absorbed by potato plants. About 44% of the absorbed Br ions could be redistributed to the soil surface when the dead leaves and vines decayed. Leaching of some chemicals, which are metabolized or degraded after being taken up by the plant, can therefore be grossly overestimated by using Br breakthrough curves under certain conditions. Before using Br as a tracer in a field experiment, preliminary laboratory studies should be conducted to determine whether Br uptake and redistribution will be significant under a particular cultivar, Br-application concentration and mode, and water-application scheme.
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