Chloride mass balance to determine water fluxes beneath KCl-fertilized crops

The utilization of Chloride Mass Balance (CMB) to determine water fluxes ge nerally has been restricted to applications in arid to semi-arid environmen ts. Only in such environments does the chloride deposited by precipitation and dry fallout concentrate sufficiently by evapotranspiration for accurate measurement. This study successfully applied CMB to dryland winter wheat p lots with 860 mm of precipitation per year: Soil cores were collected from long-term dryland winter wheat test plots located near Stillwater Oklahoma, which had known constant applications of the fertilizer KCl for the past 2 9 years. This additional chloride was sufficient to allow for accurate chlo ride concentration measurement. Groundwater recharge rates of 12.2 to 38.9 mm/y were calculated with recharge increasing with fertilizer N. These flux es may be overestimated by up to 20% based on anion exclusion measurements from adjacent soil cores. Numerical modeling of the chloride distributions beneath the plots supported the assumptions of CMB.