Maria C. Capurro, Allan Andales, Jay Ham

Abstract
Monitoring crop water requirements can improve irrigation efficiency and sustainability of irrigated agriculture. Sap flow gauges can aid in its quantification and assessment. Our objective was to develop an innovative Internet-of-Things (IoT) Sap-Flow System to measure plant transpiration in real time and incorporate an advanced decision making and diagnostic tool for irrigation management. In this study, a new type of sensor, logger and algorithms were developed to measure the water flow through plant stems just like one might measure water flow through a pipe. The sap flow gauges measure water flow rate indirectly using the Heat Pulse technique. These do-it-yourself sensors were made using a desktop 3D printer and low-cost, open-source electronics. Data from the sensors were taken every 15 minutes and transferred instantly to the cloud using IoT technology. Thus, all the information can be seen in real time from any online device from any place in the world. Sap flow was measured for a well-watered and a limited irrigated corn treatment at the IIC facility in Fort Collins, CO, during summer 2020. The gauges allowed tracking of transpiration responses to dynamic changes in weather variables and soil water. Results will improve our ability to predict corn water use, better manage irrigation and water resources. Instructions on how to build these new sensors and a printed circuit board (PCB) design for the microcontroller components, including a data storage module, will be published for others to benefit from this low-cost, open-source, IoT-based technology.