CHLORIDE MASS BALANCE TO DETERMINE WATER FLUXES BENEATH KCl-FERTILIZED CROPS

The utilization of Chloride Mass Balance (CMB) to determine water fluxes generally has been restricted toapplications in arid to semi-arid environments. Only in such environments does the chloride deposited by precipitationand dry fallout concentrate sufficiently by evapotranspiration for accurate measurement. This study successfully appliedCMB to dryland winter wheat plots with 860 mm of precipitation per year. Soil cores were collected from long-termdryland winter wheat test plots located near Stillwater, Oklahoma, which had known constant applications of the fertilizerKCl for the past 29 years. This additional chloride was sufficient to allow for accurate chloride concentrationmeasurement. Groundwater recharge rates of 12.2 to 38.9 mm/y were calculated with recharge increasing with fertilizerN. These fluxes 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.