Soil moisture heterogeneity and sensor deployment in uniformly managed field with unitextural soil

Abstract

This research investigated the spatial and temporal distribution of volumetric soil water content (VWC) and total soil water across 64 sampling locations (8 × 8 grid) in a production-scale field, reported as a unitextural soil unit by SSURGO. Consequently, the required number and placement of soil moisture monitoring locations were calculated to represent soil water status with varying degrees of variability. Each soil layer in the root zone was subject to 5-9% of mean spatial VWC variability and maximum variability as high as 21% during the 2014 and 2015 growing seasons. Total soil water showed spatial behavior, which was as high as 13%, with mean spatial variability of 5%. In 2014, the field minimum and maximum temporal CVs in VWC were 9 and 27%, respectively, which increased to 14 and 33% in 2015, respectively. Representative soil moisture and its variability were accounted for using 1-45 monitoring locations, depending on observed variability, acceptable measurement error, and confidence interval (CI). When the commonly used marginal error of 2% was considered, the numbers of sensor deployment locations were 8 (90% CI) and 11 (95% CI), which reduced to 5 (90% CI) and 4 (95% CI) sensors with 3% marginal error. We demonstrate that although SSURGO data can be valuable to make preliminary assessments, relying on it to spatially characterize soil units and their properties for effective within-soil unit management, especially for variable rate water and nutrient applications, can create significant challenges.

Temporal covariance of spatial soil moisture variations: A mechanistic error modeling approach

“…Soil moisture variability has been widely studied in relation to mean soil moisture (Bell et al., 1980; Famiglietti et al., 2008; Irmak et al., 2022; Rosenbaum et al., 2012), and in relation to the spatially variable soil properties, vegetation cover, and topography as the immediate causes of this soil moisture variability (Albertson & Montaldo, 2003; Lawrence & Hornberger, 2007; Manns et al., 2014; Pan & Peters‐Lidard, 2008; Schlüter et al., 2013; Teuling & Troch, 2005; Vereecken et al., 2007). Teuling and Troch (2005) successfully modeled soil moisture variability in a heterogeneous soil at field scale up to small catchment scale by accounting for variability in the saturated hydraulic conductivity, maximum land cover, porosity, and pore size distribution.…”