Automated Leaching Fraction-based Irrigation System Reduces Leaching, Conserves Water, and Supports Crop Growth in a Commercial Nursery

Abstract

HighlightsAn automated irrigation system based on a novel leachate sensor was built to schedule and deliver irrigation to a container nursery.The sensor network was designed to achieve a 0.15 leaching fraction; it maintained an actual average leaching fraction of 0.17.Water use and container effluent were reduced by 60% and 96%, respectively, without reducing crop growth. Abstract.With the aim of reducing irrigation water use, an irrigation and leachate measurement and control system was developed and evaluated to automatically schedule and actuate irrigation in a commercial nursery. Leachate and irrigation sensors were built using a tipping bucket mechanism and used to calculate the daily leaching fraction (LF) = volume leached/volume applied. For the experimental daily irrigation schedule, the previous day’s LF was used to calculate irrigation run time for the current day using a scaled multiplier, where the change in irrigation run time was proportional to the difference between the calculated LF and the target LF, 0.15. The control zone was irrigated for two hours every other day simulating the commercial nursery’s standard schedule. The irrigation control system worked as designed and correctly imposed the irrigation treatments, including correctly delaying in response to rain and actuating based on a programmed minimum runtime, when necessary. Season-long water use was 60% less for the leachate-based irrigation schedule compared to the grower’s standard irrigation schedule (p = 0.0028). The average daily LFs were 0.17 and 0.73 for the LF-based irrigation and control, respectively (p < 0.0001). Compared to the grower’s standard practice the time averaged irrigation application rate was 3.3-fold less and time averaged leaching rate was 12.1-fold less for the LF-based irrigation schedule. Substrate volumetric water content was not correlated with LF and thus was not a good predictor of leaching fraction. Growth metrics were not impacted by irrigation treatment (p = 0.1429), indicating plants received sufficient water in the LF-based irrigation system. This novel system was able to actuate and adjust irrigation run-time based on daily leaching fraction without being influenced by the lag between irrigation and leaching and had an average leaching fraction within 0.02 of the target LF. Reducing water use with this LF-based schedule has the potential to reduce agrichemical-laden nursery effluent and increase nursery irrigation capacity, i.e., their ability to expand production on the current water supply. Keywords: Container effluent, ET-based irrigation, Irrigation schedule, Leachate, Precision irrigation, Sensor-based irrigation.