The objective of this study was to evaluate the effectiveness of commercial
environmental sensors and public domain modeling applications in observing soil salinity
levels and salt fluxes in dairy waste lagoon irrigation operations in the San Joaquin
Valley. The physical sensors employed recorded temperature, soil moisture, and
electrical conductivity at multiple depths at two dairy sites, one characterized by clayey
soils (Clay Dairy) and the other by sandy soils (Sandy Dairy). The sensors performed
reliably with negligible temperature dependency. An exception was that high salinity in
the Clay Dairy soil led to water content overestimation that required correction. The
HYDRUS 1-D software package successfully modeled field measurements of water
content at the Sandy and Clay Dairies (R2 = 0.78, and R2 = 0.75 respectively), and overall
salinity (R2 = 0.69 and R2 = 0.72 respectively). Estimated hydraulic parameters at both
sites varied with depth but were consistent with values gleaned from the literature.
Model fits of the solute transport at the sandy site resulted in large ranges in dispersivity
values due to the scale of the soil domain. While the Clay Dairy hydraulic characteristics
were reasonably well described by the model, the model was incapable of describing
solute transport effectively, especially at the shallower depths. This result may have been
due to high dispersion, and lateral movement of water and salts not accounted for by the
1-dimensional form of the convection-dispersion equation. Long-term model projections
showed distinct peaks in water and salt during irrigation events and subsequent drainage
at both sites. The less permeable soil at the Clay Dairy facilitated greater water and
nutrient retention in the root zone, while continued irrigation at the Sandy Dairy showed
movement of salt to speculated depths of groundwater (20 to 40 meters) on a time scale of weeks, suggesting substantial salt fluxes into deep groundwater over time. Coupling
detailed monitoring with more advanced models (2D/3D, groundwater-surface water)
would prove beneficial in describing water and salt movement and accumulation in the
vadose zone and the water table to better understand the risks salinization poses to
groundwater and crop yield.