The Effect of Various Soil Hydraulic Property Estimates on Soil Moisture Simulations

TLDR: In this article, the authors used waveguides and tensiometers to obtain in situ measurements of soil moisture in unsaturated soils and applied three scaling methods to improve the performance of these measurements.

Abstract: Models of water movement in unsaturated soils require accurate representaƟ ons of the soil moisture retenƟ on and hydraulic conducƟ vity curves; however, commonly used laboratory methods and pedotransfer funcƟ ons (PTFs) are rarely verifi ed against fi eld condiƟ ons. In this study, we invesƟ gated the eff ects of using soil hydraulic property informaƟ on obtained from diff erent measurement and esƟ maƟ on techniques on one-dimensional model predicƟ ons of soil moisture content. Pairs of Ɵ me domain refl ectometry waveguides and tensiometers were installed at two depths in the side of a soil pit face to obtain in situ measurements. Undisturbed soil samples were taken near the instruments and subjected to parƟ cle size analysis, mulƟ step ouƞ low (MSO), and falling-head permeability tests to obtain esƟ mates of the soil moisture retenƟ on curves. Three scaling methods were then applied to improve the fi t of the various esƟ mates to the fi eld data. We found that soil hydraulic property esƟ mates obtained from inverse methods lead to the best simulaƟ ons of soil moisture dynamics, and that laboratory MSO tests or commonly used PTFs perform poorly. These laboratory and PTF esƟ mates can be dramaƟ cally improved, however, by simply constraining the range of possible moisture contents to the minimum and maximum measured in the fi eld. It appears that this method of scaling PTF results can be used to obtain soil hydraulic property inputs of suffi cient accuracy for plot-scale modeling eff orts without requiring expensive laboratory or in situ tests.