|Izadi, B - UNIVERSITY OF IDAHO|
|King, B - UNIVERSITY OF IDAHO|
|Mc Cann, I - UNIVERSITY OF IDAHO|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 31, 1993
Publication Date: N/A
Interpretive Summary: The movement of bromide was monitored under variable conditions observed in a furrow irrigated fallow field using soil and solution samples. The position of the Br was estimated at 0.23, 0.38, and 1.13 m after three subsequent furrow irrigation events. Occurrence of the preferential flow was hypothesized for the third irrigation based on the measurements made during and after this irrigation. Three piston flow models based on Darcy flow, field capacity, and Transfer Function theory were used to predict the movement of the solute. Overall, the field capacity model proved to be suitable for use with surface irrigation models in irrigation management studies for this type of soil. However, under extremely wet conditions (long irrigation durations) the field capacity model might fail due to the possibility of the preferential flow.
Technical Abstract: In 1991 field scale movement of bromide under the variable conditions were observed in a 0.81-ha furrow-irrigated fallow field. Twenty-one sampling stations were established, each with a soil solution sampler at 0.3-m depth, and a neutron probe access tube to a depth of 2.1 m. A narrow pulse of Br tracer was applied through a solid-set sprinkler irrigation system and was subsequently transported downwards by 26 mm of sprinkler irrigation. Three furrow irrigations were conducted during the 63-day study period. Soil samples were taken at each station in 0.15-m increments to a depth of 2.4 m prior to each irrigation and at the end of the study period. The three furrow-irrigation events moved the solute front to 0.23-, 0.38-, and 1.13-m depth, respectively. Three piston flow models based on Darcy flow, field capacity, and the Transfer Function model (TFM) were used to predict the movement of the solute. The Darcy flow model under-estimated solute movement by 18% to 43% after each irrigation event. The FTM predicted the movement of solute with reasonable accuracy after the first irrigation but overestimated solute movement for subsequent irrigations. The latter was attributed to the need to calibrate the FTM at deeper depths. The field capacity model was more consistent with observed irrigations, and predicted the movement of solute with reasonable accuracy for the first and second irrigation. However, the field capacity model underestimated the final Br position. It was hypothesized that preferential flow occurred during the third irrigation, since the infiltration rates increased during this irrigation and the final position of Br was significantly greater than predicted by the piston flow models.