Transport of bromide in the Bainsvlei soil: Field experiment and deterministic/stochastic model simulation. II. Intermittent water application

Abstract

Despite the fact that non-uniform soil water content and variable input water fluxes are usually encountered in the field, tracer experiments have usually been carried out under steady-state conditions. The objective of this study was to analyse solute transport in a Bainsvlei soil under intermittent water application using Br– as a tracer. Sprinkler was used to apply water on a plot 200 by 200 cm. Soil core samples were taken every 20 cm to a depth of 160 cm several times during the experiment. The soil Br– concentration data were fitted to the steady-state convection–dispersion analytical model in the CXTFIT package. The average coefficients of determination yielded by this fit (r2 = 0.810) clearly support that the data could be analysed successfully with CXTFIT. The average pore-water velocity of 1.72 cm/day and average dispersion coefficient of 26.19 cm2/day determined from this fit are lower than the fitted values of the steady-state experiments. The Br– moved slower under the intermittent application of water than in the steady case, a conclusion supported by the deeper location of Br– peaks under continuous application than intermittent application after the same amount of water is applied.