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Resin Adsorption for Describing Bromide Transport in Soil under Continuous or Intermittent Unsaturated Water Flow

Dep. of Plant and Soil Science, Montana State Univ., Bozeman, MT 59717-0312.

^* Corresponding author.

ABSTRACT

Accurate information on movement of soil-applied chemicals toward water tables is necessary for improving agricultural and environmental management. Current methods for studying related processes have major limitations. Objectives of this research were to investigate resin capsule adsorption for measuring Br^– transport, to compare results with those from vacuum extraction, and to determine the utility of resin capsule technology for field studies. Laboratory experiments were conducted with a uniformly packed soil column under continuous or intermittent, unsaturated water flow using Br^– as a tracer. Field experiments were also conducted with intermittent water flow applied by a line-source irrigation system. Bromide accumulated by mixedbed ion-exchange resin capsules inserted into the soil at several depths in the soil column was compared with Br^– in solutions collected at the same depths by vacuum extraction through porous ceramic candles. Delayed timing of peak Br^– leaching patterns (BLPs) at the uppermost sampling point, and earlier peak BLPs at the lowest sampling depth, when resin capsule data were used, suggest that the accuracy of measuring Br^– transport is method-dependent. Under intermittent water flow, distinct spikes of BLPs measured by resin capsules corresponded to soil water potential changes. Only broad plateaus for BLPs were measured with vacuum extraction, implying greater sensitivity of the resin capsule methodology to soil moisture changes. Field results demonstrated the utility of resin capsules for detecting Br^– transport as influenced by irrigation intensity, plant water use, and plant Br^– uptake. The resin capsule methodology may provide a simple, accurate alternative to vacuum extraction or repetitive soil sampling for studying solute transport. It provides "in situ solid-phase extraction" of the target solute simultaneously with other ions in soil solution.

Contribution no. J-2808 from the Montana Agric. Exp. Stn.

Received for publication July 7, 1992.