30
S. C. Lessoff and P. Indelman
laboratory measurements in samples from the experimental field Koc = 70 ml g-l
(Tauber-Yasur et al. 1999) and in other studies at Bet Dagan Koc = 30 ml g-l
(Gerstl and Yaron 1983). The results show no significant degradation of Bromacil
during the relatively short-term field experiment at Bet Dagan, which is in
agreement with literature reports of A. = 0.002 (Flury 1996).
The confidence interval for our model-based estimate of the infiltration rate are
0.34 <,uW < 0.60 and 0.78 < CV w < 1.7. Substituting these maximum or
minimum values into our optimization procedure produces Kd estimation
uncertainty of a similar magnitude to the Kd estimation uncertainty caused by
concentration measurement uncertainty (above). Uncertainty in the estimate of W
made no significant difference in the estimate of A..
5 Summary
Our analytic model of transient unsaturated flow and transport predicts that near
the surface under intermittent irrigation, most transport occurs during and shortly
after irrigation events. Under these conditions, the flow parameters most
important in controlling transport are the water application rate and residual soil
moisture capacity. This is in contrast to transport by steady velocity where
hydraulic conductivity is the most important flow variable.
For the chemicals tested, field-based estimates of Kd were smaller than
laboratory batch-measured values from Bet Dagan or from the literature.
Particularly for TBA (the most strongly sorbed compound), the laboratorymeasured value of the Kd (2 ml g-l) was four times the field-estimated value (0.56
ml g-l). For both TBA and BRM, the laboratory-measured Kd was outside the
confidence interval of field estimate. The field-measured value of Koc for TBA
was also significantly less than literature reported values of Koc (listed above).
Nevertheless, for Bromacil, some of the values of Koc reported in the literature are
in the upper part of our field-estimated confidence interval. For ATR, the
laboratory-measured Kd = 0.35 ml g-l was only slightly greater than the fieldmeasured value 0.28 ml g-l. Nevertheless, the field estimated Koc is less than
laboratory measurements of Koc reported in the literature. Thus, the results of both
Bet Dagan field tests (reported here and by Indelman et al. 1998) imply that shortterm field transport under intermittent irrigation can be faster than predictions
based on laboratory measurements.
The degradation rates measured at Bet Dagan were well predicted by first-order
decay rates measured in laboratory cultures and reported in the literature.
Acknowledgment, This research was partially supported by a grant of Water
Research Institute at the Technion. Thanks to 1. Dror, D. Russo, and B. Yaron for
the field data for this study.
S. C. Lessoff and P. Indelman
laboratory measurements in samples from the experimental field Koc = 70 ml g-l
(Tauber-Yasur et al. 1999) and in other studies at Bet Dagan Koc = 30 ml g-l
(Gerstl and Yaron 1983). The results show no significant degradation of Bromacil
during the relatively short-term field experiment at Bet Dagan, which is in
agreement with literature reports of A. = 0.002 (Flury 1996).
The confidence interval for our model-based estimate of the infiltration rate are
0.34 <,uW < 0.60 and 0.78 < CV w < 1.7. Substituting these maximum or
minimum values into our optimization procedure produces Kd estimation
uncertainty of a similar magnitude to the Kd estimation uncertainty caused by
concentration measurement uncertainty (above). Uncertainty in the estimate of W
made no significant difference in the estimate of A..
5 Summary
Our analytic model of transient unsaturated flow and transport predicts that near
the surface under intermittent irrigation, most transport occurs during and shortly
after irrigation events. Under these conditions, the flow parameters most
important in controlling transport are the water application rate and residual soil
moisture capacity. This is in contrast to transport by steady velocity where
hydraulic conductivity is the most important flow variable.
For the chemicals tested, field-based estimates of Kd were smaller than
laboratory batch-measured values from Bet Dagan or from the literature.
Particularly for TBA (the most strongly sorbed compound), the laboratorymeasured value of the Kd (2 ml g-l) was four times the field-estimated value (0.56
ml g-l). For both TBA and BRM, the laboratory-measured Kd was outside the
confidence interval of field estimate. The field-measured value of Koc for TBA
was also significantly less than literature reported values of Koc (listed above).
Nevertheless, for Bromacil, some of the values of Koc reported in the literature are
in the upper part of our field-estimated confidence interval. For ATR, the
laboratory-measured Kd = 0.35 ml g-l was only slightly greater than the fieldmeasured value 0.28 ml g-l. Nevertheless, the field estimated Koc is less than
laboratory measurements of Koc reported in the literature. Thus, the results of both
Bet Dagan field tests (reported here and by Indelman et al. 1998) imply that shortterm field transport under intermittent irrigation can be faster than predictions
based on laboratory measurements.
The degradation rates measured at Bet Dagan were well predicted by first-order
decay rates measured in laboratory cultures and reported in the literature.
Acknowledgment, This research was partially supported by a grant of Water
Research Institute at the Technion. Thanks to 1. Dror, D. Russo, and B. Yaron for
the field data for this study.