2018 ASHS Annual Conference

The sustainability of irrigated vegetable cropping systems is highly dependent on the effective management of water resources. This is particularly relevant in arid regions such as California which are highly impacted by climate variability and diminished water supplies. Thus, water conservation has become a top priority in the state and has required vegetable producers to adopt management practices that optimize irrigation and water use efficiency. One approach to improve irrigation efficiency is to implement irrigation scheduling practices to accurately estimate crop water requirements and determine how much and when to irrigate. Such implementation can be accurately and timely conducted with the use of sensor technology. Many sensors and data logging equipment are currently available to trigger irrigation applications based on measurements of crop evapotranspiration (ET) or soil water content. To evaluate these options and assess their effectiveness in optimizing irrigation and water use efficiency, we conducted field studies on various crops (lettuce, tomato, broccoli) which were drip-irrigated following an ET- and a soil sensor-based scheduling approach. The study site, located at California State University, Fresno, was characterized by sandy loam soils. For the ET-based approach, an irrigation scheduling program was developed to: 1) poll daily ET data from a local state weather station using the CIMIS web Application Programming Interface (API) over radio and internet links, and 2) calculate daily irrigation applications. For the sensor-based approach, six capacitance-soil moisture devices installed at three locations and two depths (6’’ and 12’’) were used with a datalogger and a 24VAC solenoid valve. Irrigation scheduling was programmed using upper (field capacity) and lower thresholds (30% maximum allowable depletion) of soil available water. Irrigation applications were triggered when the average soil moisture values reached the lower threshold and ended after field capacity was attained. In addition, some fields were irrigated based on visual crop and soil observations and manually operating irrigation valves. Results show that both ET- and soil sensor-based technology can improve water use efficiency and help growers optimize their irrigation scheduling.