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Title: WATER FLOW AND SOLUTE TRANSPORT IN FURROW-IRRIGATED FIELDS

Author
item FARIBORZ, ABBASI - UNIV. LEUVEN, BELGIUM
item FEYEN, JAN - UNIV. LEUVEN, BELGIUM
item ROTH, ROBERT - UNIV. OF ARIZONA
item SHEEDY, MIKE - UNIV. OF ARIZONA
item Van Genuchten, Martinus

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2003
Publication Date: 5/6/2003
Citation: FARIBORZ, A., FEYEN, J., ROTH, R.L., SHEEDY, M., VAN GENUCHTEN, M.T. WATER FLOW AND SOLUTE TRANSPORT IN FURROW-IRRIGATED FIELDS. IRRIGATION SCIENCE. 2003.

Interpretive Summary: Water flow and solute transport processes in the subsurface can be very complex because of the very heterogeneous makeup of most soils. Also, applying fertilizers with irrigation water (fertigation) in long borders or furrows can cause considerable fertilizer non-uniformity along the field since water and the fertilizer will reach different locations at different times depending upon the fertilizer application time and rate of advance. In this paper we present results of several field-scale solute transport experiments on 115-m long furrows to investigate the effects of flow depth and solute application time on the uniformity of solute distributions along and below the furrows. Results show a dependency of downward solute transport on flow depth and application time, and considerable non-uniformity in the solute distributions as observed at various sites along the furrows. Subsurface solute distributions below the first half-length of the furrows were much more uniform than in the second half, regardless of the irrigation regime and the solute application time. Solute distribution uniformity and application efficiency together can provide useful information about invoked fertigation practices. Fertigation is a complicated process affected by such factors as the initial water content and soil surface conditions, the adopted irrigation regime, and flow properties (e.g., inflow rate and the infiltration characteristics). Applying fertilizers during a second or third irrigation, rather than only the first irrigation, may improve the solute distribution uniformity and application efficiency since the effects of several of those factors (e.g., initial condition, infiltration, and roughness properties) can substantially decrease during the second and particularly subsequent irrigations. Results of this study are important for understanding the effects of field-scale heterogeneity on subsurface water flow and solute transport in general, and for implementing furrow irrigation practices that improve water and solute uniformities in the subsurface.

Technical Abstract: Field-scale solute transport experiments are not easily implemented because of the overwhelming problems of soil heterogeneity and variability in subsurface hydraulic and solute transport properties. In this paper, the results of four field-scale furrow irrigation experiments designed to investigate the effect of flow depth and solute application time on bromide distribution along and below the furrows are presented. One experiment was conducted under free-draining (FD) conditions in which bromide was applied during the entire irrigation event. Thee experiments were carried out on blocked-end furrows in which bromide was injected either during the entire irrigation event (100 percent), the first half of the irrigation (FH), or the second half of the irrigation (SH). The FD experiment was equipped with neutron probe tubes for measuring soil water contents at different times and locations in furrow cross-sections, whereas soil samples for bromide analysis and gravimetric soil water contents from all experiments were collected at different depths up to 1.80 m, 5 days after the irrigation at three locations near the inlet, in the middle, and close to the outlet of the furrows. Overland flow depths along the furrows were also recorded using staff gauges at the inlet, middle and outlet sites every few minutes during the entire irrigation. Results showed substantial non-uniformity in solute movement along the monitored furrows, with the degree of non-uniformity depending upon flow depth level and solute application time. Non-uniform distributions were observed especially at the outlet sites, compared to those at the inlet and middle sites. Solute application efficiencies for the FD, 100 percent, FH, and SH experiments were 50, 100, 64, and 93 percent, respectively. The effects of water level and irrigation/solute application time on soil water contents were more pronounced in the soil surface layers and were found to be relatively minor at deeper depths. Water and solute deep percolation rates also showed dependency to flow depth and solute application/opportunity time, and gradually decreased along the furrows.