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Rate-Limited Boron Transport in Soils: The Effect of Soil Texture and Solution pH

Institute of Soil, Water and Environmental Sciences, the Volcani Center, Agricultural Research Organization (ARO), P.O. Box 6, Bet Dagan 50250, Israel

View larger version (16K): [in a new window]   Fig. 1. Results of B adsorption kinetic experiments: a fraction of aqueous B initial concentration vs. time. Symbols represent the experimental points and solid lines represent concentrations calculated using Eq. [23] and data set of Table 2.

View larger version (25K): [in a new window]   Fig. 2. (a)Boron adsorption isotherm for the sandy loam soil and (b) Langmuir plots of data at different pH values. Experimental points and the lines calculated using Eq. [3] and [4] and the adsorption coefficients bm, kBH, kB– and kOH of Table 3 are presented.

View larger version (25K): [in a new window]   Fig. 3. (a) Boron adsorption isotherm for the clay soil and (b) Langmuir plots of data at different pH values. Experimental points and the lines calculated using Eq. [3] and [4] and the adsorption coefficients bm, kBH, kB–, and kOH of Table 3 are presented.

View larger version (16K): [in a new window]   Fig. 4. Apparent adsorption coefficient k as a function of pH. The lines are calculated using Eq. [4] and the adsorption coefficients bm, kBH, kB–, and kOH of Table 3. Open and solid symbols represent k values obtained from batch kinetic and equilibrium experiments, respectively.

View larger version (21K): [in a new window]   Fig. 5. Measured and fitted breakthrough curves for Br– transport in the loamy sand and sandy loam soils at water fluxes, q of 2.9 and 0.19 cm h–1. Symbols represent the measured Br– concentrations. Solid lines were obtained by fitting the CDE to the fast and slow-velocity data (best-fit values for Pe are given in Table 5).

View larger version (27K): [in a new window]   Fig. 6. Measured and fitted breakthrough curves for Br– transport in the clay soil at water fluxes, q of 2.9 and 0.19 cm h–1. Solid lines were obtained by fitting the TD model to the fast and slow-velocity data (best-fit values for Pe, , and 0 are given in Table 5).

View larger version (31K): [in a new window]   Fig. 7. Measured, fitted and predicted B breakthrough curves for the loamy sand soil at pH 7 and 9, and water fluxes, q of 2.9 and 0.19 cm h–1. Symbols represent the measured B concentrations (the average values from the two parallel experiments). Dashed line was calculated by the LE-NE model for the fast-velocity data at pH7 using the rate coefficient of Table 2 and solid lines were obtained by fitting the LE-NE model to the fast-velocity data at pH 7 and 9 (best-fit values f and 0 are given in Table 6) and by predicting the slow-velocity data at pH 7 and 9.

View larger version (31K): [in a new window]   Fig. 8. Measured, fitted and predicted B breakthrough curves for the sandy loam soil at pH 7 and 9, and water flow rates, q of 2.9 and 0.19 cm h–1. Dashed line was calculated by the LE-NE model for the fast-velocity data at pH7 using the rate coefficient of Table 2 and solid lines were obtained by fitting the LE-NE model to the fast-velocity data at pH 7 and 9 (best-fit values f and 0 are given in Table 6) and by predicting the slow-velocity data at pH 7 and 9.

View larger version (37K): [in a new window]   Fig. 9. Measured, fitted and predicted B breakthrough curves for the clay soil with aggregate sizes <2 mm and 4.0 through 4.75 mm and water flow rates, q of 2.9 and 0.19 cm h–1. Solid lines were obtained using the TD-TR model (best-fit values for 0 are given in Table 6). Dashed lines represent predictions made by the TD adsorption (ad) model of van Genuchten–Wierenga.