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2019 ASHS Annual Conference

Assessing Tipping Bucket-Based Irrigation and Leachate Sensor Performance

Wednesday, July 24, 2019
Cohiba 5-11 (Tropicana Las Vegas)
Quinn Cypher, University of Tennessee, Knoxville
Wesley Wright, University of Tennessee, Knoxville
Amy Fulcher, University of Tennessee, Knoxville, TN
Lauren Fessler, University of Tennessee, Knoxville, TN
Jeff McHugh, University of Tennessee, Knoxville
Sun Xiaocun, University of Tennessee, Knoxville, TN
Woody nursery crops are typically grown in bark-based substrates with low water holding capacities. Coarse substrates and static irrigation scheduling can waste water and leach pesticides and nutrients. Leaching fraction-based irrigation scheduling has the potential to conserve water and align irrigation with crop and environmental demand. The leaching fraction from a single irrigation event can be calculated from manually collected volume or gravimetric measurements. The objective of this research was to develop a reliable sensor for measuring irrigation or leachate volume that could be used as part of a system that would automatically calculate leaching fraction, determine irrigation operation time, and actuate irrigation accordingly. Sensors were composed of a tipping bucket assembly within a 6-inch (15.2-cm) diameter PVC pipe topped with a funnel to channel effluent from the container. A container-grown plant was placed on the funnel with a shield to prevent rain and overhead irrigation from entering the assembly. Leachate sensors were built and deployed, with twenty sensors at each of two nurseries in 2015. Sensors were calibrated to 0.28 fl oz (4.73 ml) per tip in spring 2017 at both nurseries and spring of 2018 at one. Post-calibration volume measurements recorded at the beginning of the season were compared with end of season volume measurements taken 4 to 6 months later with the same gauges. Volume was measured after applying 100 ml of water at a predetermined flow rate. Data were analyzed using a random block design with repeated measures with nursery as the block effect and season (spring or fall) as the repeated factor. Data were rank transformed prior to analysis due to non-normality and unequal variance. Multiple comparisons were performed with Tukey’s adjustment. Equivalency tests, conducted with two one-sided tests (TOST), were performed using a 3% (3-ml), 5% (5-ml), and 10% (10-ml) threshold to assess if there was a practical difference in means. There was no effect of season; end of season measurements did not differ from spring post-calibration measurements (P-value = 0.4050). Means were not equivalent at 3% (P-value = 0.6785) or 5% (P-value = 0.3170) but were equivalent at 10% (P-value = 0.0029). An affordable sensor was developed for measuring irrigation or leachate volume in real-time nursery conditions. Additional studies assessing a system that integrates these sensors with a data logger to calculate leaching fraction from irrigation and leachate volume and actuate irrigation run time based on a target leaching fraction are ongoing.