For sustainable crop growth, timely irrigation of the crops is critical in getting optimum yields. With the availability of inexpensive electronics components, the Internet of Things (IoT) has become a significant development in automating irrigation. Precise estimation of the crop evapotranspiration (ET) is crucial for determining the depth of water to be applied in the field. At present, atmometers or weather data are used to estimate the crop ET.  The atmometer assumes that the crop has been well-watered, and it does not take into account the reduction of ET during the soil limiting phase when the plant transpiration rate is not maximum. Therefore, an ET estimation method that considers the soil moisture status will give a more accurate crop ET.

The primary objectives of this study are to build a plant-controlled atmometer and evaluate it to measure the crop ET for irrigation scheduling using IoT accurately. In this experiment, an atmometer will be built based on a variable evaporation rate controlled not only by the weather conditions but also by the soil water status. The design required an Arduino UNO, soil moisture sensor, pressure transducer, solenoid valve, GSM module, and a load cell. Experiments on evaporation rate via porous plates have demonstrated that evaporation rate could be controlled by reducing the back pressure on the water supply side. This relationship can alter the atmometer's water evaporation rate to mimic the reduced ET due to the decrease in water content of the soil within the root zone. A soil water content sensor embedded within the crop root zone can regulate the variation in evaporation rate from the atmometer and mimic the crop ET more accurately. The actual ET of the crop will be determined by measuring the water content changes within the root zone, and this will be compared with the ET measured by the plant-controlled atmometer. The crop ET data measured by the plant-controlled atmometer will be sent to the cloud server by the GSM module. The data from the cloud will be pushed to the farmer’s smartphone to provide the depth of irrigation information before irrigation or when an irrigation set-point has been reached in the field.

Keywords: Plant-controlled Atmometer, Evapotranspiration, Evaporation rate, Arduino UNO, Soil moisture sensors, GSM module