Distributed control and data acquisition system for closed-loop site-specific irrigation management with center pivots

The development of spatially variable irrigation requirements under conventional uniform irrigation management means that optimum irrigation scheduling on the field scale is not achievable, resulting in less than maximum water and nutrient use efficiency. Research and development of site-specific irrigation management technology to address this issue began over a decade ago. However development of an integrated distributed control and data acquisition to meet the unique requirements of site-specific irrigation management has received little attention. A conceptual model for closed-loop site-specific irrigation with center pivot irrigation systems is presented. A distributed control and data acquisition (DCADA) system to implement the conceptual model was constructed and field tested. The DCADA system uses network nodes mounted on the center pivot lateral and stationary network nodes located in the field to allow a master control computer to vary water application rate along the system lateral based on near-real time measurements of soil water status. Power line carrier and radio frequency communication media are combined to link the system mounted controls and in-field sensors as a single distributed network. The DCADA system was installed on a 4-span, 191-m (628-ft) center pivot irrigation system and used to impose site-specific and conventional uniform irrigation treatments to a potato crop in one 2.9-ha (7.1-acre) quadrant of the field. Field average seasonal water application was essentially equal under both irrigation management treatments, but water application under site-specific irrigation management varied from 86 to 119% of conventional uniform irrigation management. Total tuber yield averaged across the field site was significantly (P <= 0.10) greater by approximately 4% under site-specific irrigation management. Tuber yield per unit of applied irrigation water was greater by approximately 5% under site-specific irrigation management. The DCADA system provided an effective means to implement site-specific irrigation management with a center pivot system using near real-time soil water monitoring.