Soil Moisture and Water Transport through the Vadose Zone and into the Shallow Aquifer: Field Observations in Irrigated and Non-Irrigated Pasture Fields

Abstract

Reliable estimates of soil moisture and other field observations (e.g., precipitation, irrigation) are critical to quantify the seasonal variability of surface water and groundwater relationships. This is especially important in pasture-based agroecosystems that rely on surface water diversions and precipitation inputs for agricultural production. The objectives of this study were to (1) quantify soil water balance components in irrigated and non-irrigated pasture fields in western Oregon, USA and (2) evaluate soil moisture and shallow aquifer recharge relationships in irrigated vs. non-irrigated pasture fields. Four monitoring stations in each field were used to measure soil water content in the upper 0.8 m profile and shallow groundwater levels. A soil water balance (SWB) approach was used to determine deep percolation based on field measurements of several other hydrology variables (e.g., irrigation and soil moisture). The water table fluctuation method (WTFM) was used to estimate shallow aquifer response to irrigation and precipitation inputs. Results from this study add to the understanding of seasonal water transport through the vadose zone and into the shallow aquifer in agroecological systems with fine-textured soils in the Pacific Northwest region of the United States.