|Van Genuchten, Martinus|
|Hunsaker, Douglas - Doug|
Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2002
Publication Date: 4/1/2003
Citation: Abbasi, F., Simunek, J., Van Genuchten, M.T., Feyen, J., Adamsen, F.J., Hunsaker, D.J., Strelkoff, T., Shouse, P.J. 2003. Overland water flow and solute transport: model development and field-data analysis. Journal of Irrigation and Drainage Engineering. Vol 129:71-81 Interpretive Summary: Fertilizers are widely applied to agricultural fields using surface fertigation, i.e., application of fertilizers with irrigation water. However, there are still no adequate guidelines for the proper design and management of surface fertigation. The method has certain advantages as compared to conventional application methods, such as reduced energy, labor, soil compaction, and machinery costs. Moreover, it allows growers to apply nutrients in small amounts throughout the season in response to crop needs without the possibility of crop damage or soil compaction caused by mechanized application methods. In this study we developed a combined overland water flow and solute transport model, and used the model to evaluate several alternative fertigation practices commonly employed in furrow irrigation field experiments. Four large-scale field experiments were conducted on blocked-end and free draining furrows to calibrate and verify the proposed model. The model showed good agreement with all field data. Both the field measurements and the model predictions showed that application of fertilizers during either the entire irrigation event or the second half of the irrigation, resulted in higher solute uniformity in the soil. Results should be of interest to both modelers and field practitioners trying to devise and implement improved and more cost-effective surface fertigation methods
Technical Abstract: The application of plant nutrients with irrigation water is an efficient and cost-effective method for fertilizer application to enhance crop production and reduce or eliminate potential environmental problems related to conventional application methods. In this study, a combined overland water flow and solute transport model for analysis and management of surface fertigation/chemigation is presented. Water flow is predicted with the well-known Saint-Venant's equations using a control volume of moving cells, while solute transport is modeled with the advection-dispersion equation. The 1D transport equation was solved using a Crank-Nicholson finite difference scheme. Four large-scale field experiments were conducted on blocked-end and free draining furrows to calibrate and verify the proposed model. The results showed that application of solute during the entire irrigation event, or during the second half of the irrigation for blocked end conditions with appropriate inflow rates, produced higher solute uniformity than application of solute during the first half of the irrigation event. Measured fertilizer distribution uniformity of the low quarter ranged from 21 to 76 percent while fertilizer distribution uniformity of the low half values varied between 62 to 87 percent. The model was subsequently applied to the experimental data; results showed good agreement with all field data. Water balance errors for the different experiments varied from 0.004 to 1.8 percent, whereas fertilizer mass balance errors ranged from 1.2 to 3.6 percent. A sensitivity analysis was also performed to assess the effects of longitudinal dispersivity parameter on overland solute concentrations. A value of 10 cm for dispersivity provided a reasonable fit to the experimental data.