18
S. C. Lessoff and P. Inde1man
surface fit a lognonnal curve with a coefficient of variation of 0.5. The area
covered by the sprinklers was approximately 200 m 2 and, therefore, the irrigation
efficiency was estimated as 60%. Thus, for each irrigation event the total volume
reaching the experimental plot was estimated as 30 mm.
Two days after the first, fourth, and tenth irrigation events, soil cores were
taken at 28 randomly detennined sample points and divided into seven depth
intervals. Samples were transferred to plastic bags in the field and immediately
refrigerated. Herbicide concentrations in laboratory extractions from the soil
samples were measured using a gas chromatograph with a nitrogen-phosphorus
detector.
Moisture content was measured gravimetrically in each soil sample. By the
time of sampling, rapid changes in soil moisture content, B, had ceased. Therefore,
the measured moisture content was used as an estimate of the field capacity
moisture content, Be. The moisture content fit a nonnal distribution with a mean of
0.l3 and coefficient of variation 0.2.
In a separate experiment on the same field, the conservative tracer calcium
bromide (CaBr) was applied to the field at a rate of 55 g m- 2 • The field was
irrigated with 50 mm of water over a ta = 6-h period on the 4th day and again on
the 17th day after tracer application. Cores were taken at 28 sample points 6 days
after chemical application and at 15 sample points 19 days after chemical
application. At 7 depth intervals in each core, moisture content was measured
gravimetrically and bromide ion concentration was measured in aqueous
extractions using an ion chromatograph with a conductivity detector.
The saturated hydraulic conductivity (Ks) at the site was measured in situ by
Russo et al. (1997) using Guelph permeameters. The measured Ks distribution best
fit a lognormal distribution with mean of In Ks of 2.54 in cm dafl and variance of
In Ks of 1.24. The integral scale of In Ks was 0.8 m and nearly isotropic in the
horizontal plane and 0.2 m in the vertical direction.
Tauber-Yasur et al. (1999), measured sorption in batch experiments on soil
samples from Bet Dagan. Sorption reached equilibrium in 24 h and the mean
linear equilibrium sorption coefficient was f.iKd = 0.6 and 2. ml g-I for BRM and
TBA, respectively. Shapir and Mandelbaum (1997) measured sorption and
degradation of A TR in batch experiments on soil samples from two profiles from
the experimental plot. In the experimental zone (above 1.2 m) f.iKd was 0.4 ml g-I.
The exponential decay rate A of A TR in unamended Bet Dagan soil cultures was
approximately 0.02 day-I from 0-25 cm depth, 0.01 day-I from 50-255 cm depth
and 0.006 dafl from 370-400 cm depth.
3 Flow and Transport Model
The purpose of this section is to derive relationships between field-scale transport
and laboratory-measured properties. To achieve this aim, we extend the column
model of flow and transport suggested by Dagan and Bresler (1979) and modified
S. C. Lessoff and P. Inde1man
surface fit a lognonnal curve with a coefficient of variation of 0.5. The area
covered by the sprinklers was approximately 200 m 2 and, therefore, the irrigation
efficiency was estimated as 60%. Thus, for each irrigation event the total volume
reaching the experimental plot was estimated as 30 mm.
Two days after the first, fourth, and tenth irrigation events, soil cores were
taken at 28 randomly detennined sample points and divided into seven depth
intervals. Samples were transferred to plastic bags in the field and immediately
refrigerated. Herbicide concentrations in laboratory extractions from the soil
samples were measured using a gas chromatograph with a nitrogen-phosphorus
detector.
Moisture content was measured gravimetrically in each soil sample. By the
time of sampling, rapid changes in soil moisture content, B, had ceased. Therefore,
the measured moisture content was used as an estimate of the field capacity
moisture content, Be. The moisture content fit a nonnal distribution with a mean of
0.l3 and coefficient of variation 0.2.
In a separate experiment on the same field, the conservative tracer calcium
bromide (CaBr) was applied to the field at a rate of 55 g m- 2 • The field was
irrigated with 50 mm of water over a ta = 6-h period on the 4th day and again on
the 17th day after tracer application. Cores were taken at 28 sample points 6 days
after chemical application and at 15 sample points 19 days after chemical
application. At 7 depth intervals in each core, moisture content was measured
gravimetrically and bromide ion concentration was measured in aqueous
extractions using an ion chromatograph with a conductivity detector.
The saturated hydraulic conductivity (Ks) at the site was measured in situ by
Russo et al. (1997) using Guelph permeameters. The measured Ks distribution best
fit a lognormal distribution with mean of In Ks of 2.54 in cm dafl and variance of
In Ks of 1.24. The integral scale of In Ks was 0.8 m and nearly isotropic in the
horizontal plane and 0.2 m in the vertical direction.
Tauber-Yasur et al. (1999), measured sorption in batch experiments on soil
samples from Bet Dagan. Sorption reached equilibrium in 24 h and the mean
linear equilibrium sorption coefficient was f.iKd = 0.6 and 2. ml g-I for BRM and
TBA, respectively. Shapir and Mandelbaum (1997) measured sorption and
degradation of A TR in batch experiments on soil samples from two profiles from
the experimental plot. In the experimental zone (above 1.2 m) f.iKd was 0.4 ml g-I.
The exponential decay rate A of A TR in unamended Bet Dagan soil cultures was
approximately 0.02 day-I from 0-25 cm depth, 0.01 day-I from 50-255 cm depth
and 0.006 dafl from 370-400 cm depth.
3 Flow and Transport Model
The purpose of this section is to derive relationships between field-scale transport
and laboratory-measured properties. To achieve this aim, we extend the column
model of flow and transport suggested by Dagan and Bresler (1979) and modified