The Relationship Between Sap Flow and Commercial Soil Water Sensor Readings in Irrigated Potato (Solanum tuberosum L.) Production

Many irrigation scheduling methods utilized in commercial production settings rely on soil water sensors that are normally purchased as off-the-shelf technology or through contracted services that install and monitor readings throughout the season. These systems often assume a direct relationship between the parameters measured by these soil water sensors (voltage, unitless values, or calibrated soil moisture values) and the water use and deficit stress of the crop. Because of this assumed relationship, these sensors are purported to be useful for triggering irrigation applications by monitoring relative changes in sensor values that represent either a "dry" or "wet" condition in the field. However, there is often little confirmation that these sensors accurately reflect crop water uptake or what soil depths will best represent that relationship. In an attempt to quantify the association between the use of soil water sensors and crop water use in a commercial potato field, measurements of soil water using capacitance probes and plant water use using sap flow sensors were monitored. Measurements were taken in two water application treatments: a normal (full) and partial irrigation schedule because it was hypothesized that the relative strength of the relationship between sensor reading and crop water use may be highly dependent on field soil water status. Relative soil moisture readings and plant water use data were compiled and both linear and quadratic regressions were performed. The correlation between sap flow and soil sensor readings was significant; but the relationship was relatively weak with the strength dependent on the soil depth that was monitored, indicating that care must be taken when utilizing sensor readings for irrigation scheduling.