Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2002
Publication Date: 9/1/2002
Citation: BLANCO-CANQUI, H., GANTZER, C.J., ANDERSON, S.H., ALBERTS, E.E. SATURATED HYDRAULIC CONDUCTIVITY OF A MEXICO CLAYPAN SOIL. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL. 2002. V. 66. P. 1596-1602.
Interpretive Summary: About one-half the volume of any soil is comprised of soil pores whose size distribution impacts the amount and rate of water movement into and through the soil. Saturated hydraulic conductivity (Ksat) is an important measurement used to define the rate that water moves through the soil pore system when it is saturated. Ksat can be measured in the field (in-situ measurement) and in the laboratory on undisturbed soil samples. Research has shown much variability in laboratory measured Ksat values, primarily due to the size and number of macropores. This study compared results from in-situ measurements of Ksat to those made in the laboratory with the macropores left open or sealed with bentonite. There was very good agreement between in-situ Ksat values and those measured in the laboratory when bentonite was used to seal the macropores. The Ksat values we measured were used in the Water Erosion Prediction Project (WEPP) model to predict runoff for comparison to measured values from a long-term plot study. We found that predicted runoff agreed well with measured runoff. Ksat values from other studies were generally higher than ours, and when used in the WEPP model, caused the predicted values to be lower than those measured. Our results will be useful in developing more accurate procedures for measuring Ksat in the laboratory by eliminating macropore flow with bentonite. Our results also show the sensitivity of the WEPP model to Ksat values, which will be useful to users of this erosion prediction technology.
Technical Abstract: Saturated hydraulic conductivity (Ksat) is an essential parameter for understanding infiltration and water redistribution in the soil. This study evaluated the Ksat of in-situ monoliths and intact cores and compared the results to other studies for the Mexico soil. The Ksat values were then used as runoff model input to assess the impact of Ksat differences on npredicted runoff. Lateral in-situ Ksat of the topsoil was determined on 250-mm by 50-mm by 230-mm deep monoliths. These values were compared with the Ksat of 76-mm by 76-mm diameter intact cores with and without bentonite to seal macropores. The lateral in-situ Ksat was 72 +/- 0.7 mm h**-1. The core Ksat without bentonite (312 +/- 58 mm h**-1) was larger than the lateral in-situ Ksat (p=0.03). The monolith Ksat was not different from core Ksat with bentonite (71 +/- 1.1 mm h**-1). The intact core Ksat with bentonite differed from previous studies by one order of magnitude, which shows the importance of sealing macropores in laboratory Ksat measurements Predicted runoff using the Water Erosion Prediction Project (WEPP) model varied as much as 25% in response to changes in effective Ksat. The effective Ksat of six other studies for Mexico soils underestimated runoff. The Ksat of cores with bentonite correlated well with measured runoff from long-term plot studies. A quadratic regression explained 95% of the variability between predicted and measured runoff. Researchers should be aware that using unverified hydraulic parameters for model input values can cause inaccurate predictions.