Graduate Thesis Or Dissertation
 

Computer simulation to control environmental impact of water and nitrate leaching in furrow irrigated fields

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1g05ff709

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  • Nitrate contamination in ground and surface waters is of great concern to environmentalists. A two-dimensional model of water and solute movement in soils was used to test the usefulness and relative advantages of a two-dimensional model over a one dimensional model for analysis of deep percolation and nitrate leaching in furrow irrigation. The predictive ability of the model was evaluated using data collected in a series of preliminary field studies. Two methods were used to calibrate the model. First, the cumulative infiltration simulated by the model was compared with an infiltration curve derived from field data. Secondly, soil water potential data were used to compare the observed movement of a wetted front in the soil profile. The calibration results closely followed the two dimensional flow pattern in furrow irrigation. The model was used both in a one-dimensional mode and a two-dimensional mode. Comparison of one-dimensional and two-dimensional models was accomplished using the two-dimensional model, with uniform infiltration across the surface boundary to represent the one-dimensional case, and with infiltration only across the furrow surface for the two-dimensional case. Evaluation of water and nitrate leaching was observed for alternate furrow irrigation as well as every-furrow irrigation with three different furrow spacings; 76, 86, and 102 cm. These results showed that the one-dimensional model always under estimates the leaching amount in comparison to the two-dimensional model. In some cases the one-dimensional model predicted no leaching of water and nitrate below the root zone though leaching was predicted by the two-dimensional model. Evaluation of alternate and every furrow irrigation with different furrow spacing indicated that the leaching amount increased rapidly with the increase of furrow spacing. Under furrow irrigation, attempts to irrigate the soil profile to a level less than, but close to, field capacity will result in leaching. Therefore different irrigation management is needed to minimize leaching. Additionally, the model suggests that the sealing layer which forms in the bottom of the furrow drastically reduced the infiltration rate because of the very low saturated hydraulic conductivity in that area. Sealing layer had a significant effect on the performance of SWMS_2D model, and made the model unusable where high input volume were required.
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