Implementation of a Soil Water Extraction Model on a Spatial Domain Using Field Capacity and Apparent Electrical Conductivity Relationships

Abstract

<abstract><title><italic>Abstract.</italic></title> Relationships were developed between apparent electrical conductivity (EC_a) measured using a Veris 3100 conductivity instrument (Veris Technologies, Inc., Salina, Kans.) and soil hydraulic parameters [field capacity (FC) and permanent wilting point (PWP)] for use in a soil water extraction model to estimate spatial and temporal changes in maize (Zea mays L.) soil water extraction and plant-available water (PAW) at the South Central Agricultural Laboratory near Clay Center, Nebraska, in 2012. Linear relationships were observed between soil hydraulic parameters and EC_a for the top 0.30 m depth, and curvilinear relationships were observed for the sub-layer (0.30-0.90 m). Stronger relationships were observed for the top 0.30 m depth, with R² and RMSD of 0.68 and 0.008 m³ m^-3 for FC and 0.83 and 0.008 m³ m^-3 for PWP, respectively, than for the 0.30 to 0.90 m depth, with R² and RMSD of 0.35 and 0.008 m³ m^-3 for FC and 0.39 and 0.007 m³ m^-3 for PWP, respectively. Spatial and temporal variability in soil water extraction was observed in the 0-0.30 m, 0.30-0.60 m, and 0.60-0.90 m soil depths as well as PAW in the 0.90 m soil profile using the FC vs. EC_a regressions in the soil water extraction model. Irrigation treatment differences were apparent, with less soil water extraction in the 0.30-0.90 m soil layer under rainfed than irrigated conditions. The soil water extraction model using the developed FC vs. Veris EC_a regressions performed satisfactorily compared to soil water balance determined seasonal profile (0-0.90 m) actual crop evapotranspiration (ET_a), with a resulting R² and RMSD of 0.72 and 27 mm, respectively. Further research is needed to investigate different EC_a sensors as well as different methods for developing relationships between soil hydraulic parameters and EC_a, which can include incorporating spatial variability in topsoil and subsoil depth thicknesses prior to regression analysis. The research findings reported here should lead to additional analyses and research for using EC_a as an indirect estimator for soil hydraulic parameters for use in estimating soil water extraction and PAW.