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Title: SENSITIVITY OF TILE DRAINAGE FLOW AND CROP YIELD ON MEASURED AND CALIBRATED SOIL HYDRAULIC PROPERTIES

Author
item Ma, Liwang
item Malone, Robert - Rob
item Heilman, Philip - Phil
item Ahuja, Lajpat
item Meade, Terry
item ANAPALLI, SASEENDRAN - COLORADO STATE UNIVERSITY
item Ascough Ii, James
item KANWAR, R. - IOWA STATE UNIVERSITY

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2006
Publication Date: 5/16/2007
Citation: Ma, L., Malone, R.W., Heilman, P., Ahuja, L.R., Meade, T.G., Anapalli, S.S., Ascough Ii, J.C., Kanwar, R.S. 2007. Sensitivity of tile drainage flow and crop yield on measured and calibrated soil hydraulic properties. Geoderma 140:3(2007) 284-296. Published on-line 5/16/2007. doi:10.1016/j.geoderma.2007.04.012

Interpretive Summary: Process-based agricultural systems models require detailed description of soil hydraulic properties that are usually not available. The objectives of this study were to evaluate the sensitivity of model simulation results to uncertainty in measured soil hydraulic properties and to compare simulation results using measured and default soil parameters. To do so, we measured soil water retention curves and saturated soil hydraulic conductivity (Ksat) from intact soil cores taken from a long-term experimental field near Nashua, Iowa for the Kenyon-Clyde-Floyd-Readlyn soil association. The soil water retention curves can be well described using the pore size distribution index ('). Measured ' values from undisturbed soil cores ranged from 0.04 to 0.12 and the measured Ksat values ranged from 1.8 to 14.5 cm/hr. These hydraulic properties were then used to calibrate the Root Zone Water Quality Model (RZWQM) for simulating soil water content, water table, tile drain flow, and crop yield (corn and soybean) by optimizing the lateral Ksat (LKsat) and hydraulic gradient (HG) for subsurface later flow. The measured soil parameters provided better simulations of soil water storage, water table, and N loss in tile flow than using the default soil parameters based on soil texture classes in RZWQM. Sensitivity analyses were conducted for ', Ksat, saturated soil water content ('s) or drainable porosity, LKsat, and HG using the Latin Hypercubic Sampling (LHS) and for LKsat and HG using a single variable analysis. Results of sensitivity analyses showed that RZWQM simulated yield and biomass were not sensitive to soil hydraulic properties. Simulated tile flow and N losses in tile flow were not sensitive to ' and Ksat either, but they were sensitive to LKsat and HG. Further sensitivity analyses using a single variable showed that LKsat in the tile layer was a more sensitive parameter compared to LKsat in other soil layers, and HG was the most sensitive parameter for tile flow under the experimental soil and weather conditions.

Technical Abstract: Process-based agricultural systems models require detailed description of soil hydraulic properties that are usually not available. The objectives of this study were to evaluate the sensitivity of model simulation results to uncertainty in measured soil hydraulic properties and to compare simulation results using measured and default soil parameters. To do so, we measured soil water retention curves and saturated soil hydraulic conductivity (Ksat) from intact soil cores taken from a long-term experimental field near Nashua, Iowa for the Kenyon-Clyde-Floyd-Readlyn soil association. The soil water retention curves can be well described using the pore size distribution index ('). Measured ' values from undisturbed soil cores ranged from 0.04 to 0.12 and the measured Ksat values ranged from 1.8 to 14.5 cm/hr. These hydraulic properties were then used to calibrate the Root Zone Water Quality Model (RZWQM) for simulating soil water content, water table, tile drain flow, and crop yield (corn and soybean) by optimizing the lateral Ksat (LKsat) and hydraulic gradient (HG) for subsurface later flow. The measured soil parameters provided better simulations of soil water storage, water table, and N loss in tile flow than using the default soil parameters based on soil texture classes in RZWQM. Sensitivity analyses were conducted for ', Ksat, saturated soil water content ('s) or drainable porosity, LKsat, and HG using the Latin Hypercubic Sampling (LHS) and for LKsat and HG using a single variable analysis. Results of sensitivity analyses showed that RZWQM simulated yield and biomass were not sensitive to soil hydraulic properties. Simulated tile flow and N losses in tile flow were not sensitive to ' and Ksat either, but they were sensitive to LKsat and HG. Further sensitivity analyses using a single variable showed that LKsat in the tile layer was a more sensitive parameter compared to LKsat in other soil layers, and HG was the most sensitive parameter for tile flow under the experimental soil and weather conditions.