The relationship between sap flow and commercial soil water sensor readings in irrigated potato (Solanum tuberosum L.) production

Authors: BYRD, SETH - University Of Florida; ROWLAND, DIANE - University Of Florida; BENNETT, JERRY - University Of Florida; ZOTARELLI, LINCON - University Of Florida; WRIGHT, DAVID - University Of Florida; Alva, Ashok

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2015
Publication Date: 8/15/2015
Citation: Byrd, S.A., Rowland, D.L., Bennett, J., Zotarelli, L., Wright, D., Alva, A.K. 2015. The relationship between sap flow and commercial soil water sensor readings in irrigated potato (Solanum tuberosum L.) production. American Journal of Potato Research. doi:10.1007/s12230-015-9471-7.

Interpretive Summary: Optimal scheduling of irrigation for any crop is critical to maintain high production and high quality of crop products, with minimal loss of water that can result in loss of nutrients and contribute to potential groundwater contamination. Automated sensors are often used for real time monitoring of the soil water content to estimate the water deficit in the root zone as basis to replenish the water deficit. This approach excludes any measurement of crop indices for water availability or deficit. In this study, ‘Frito Lay’ potato cultivar grown in a fine sandy soil with center pivot irrigation was used. Capacitance probes were used for real time monitoring of soil water content in the soil profile. Full irrigation, i.e. no water stress, and deficit irrigation, i.e. skip every third irrigation, were used. Sap flow measurements were also done on four plants near very close to the soil water sensors. This study revealed good relationship between the changes in soil water content by the sensor and the sap flow measurements. However, it is important to have a clear understanding of the soil depth to represent bulk of water uptake by the plants and use this depth in developing irrigation set points using the soil water sensors.

Technical Abstract: 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 Bdry^ or Bwet^ 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.