Tensiometer actuated automatic micro irrigation of apples

Irrigation scheduling by soil sensor feedback enables us to keep the root zone in preset water potential ranges to obtain desired plant responses, as high yields, good fruit quality and restrained vegetative growth. Recent developments in sensor technology and irrigation control enable us to test this old idea in a four-year field experiment at the Matityahu experimental station. Tensiometers equipped with vacuum transducers were interfaced with a Campbell micrologger to a MIR 5000 irrigation controller. Microsprinklers and one or two drip laterals per tree row, were opened at-15, -25 and -35 kPa thresholds, and closed when the wetting front reached the sensors. The system functioned well technologically. At equal thresholds, two drip laterals consumed more water than a single line, and microsprinklers more than two laterals. Water application was a descending function of irrigation thresholds and yields in turn were function of wa ter application. 15-20 kPa was found to be the appropriate actuation threshold for single lateral drip irrigation, 20-25 for two laterals. Spatial variability of the wetted volume was the main obstacle when tensiometers were inserted 0.3 m from the tricklers.