Improving water and fertilizer use efficiency during the production of strawberry in coir substrate hydroponics using a FDR sensor-automated irrigation system

Water drainage from open hydroponic systems often causes significant environmental pollution (due to the use of agrochemicals) and leads to the loss of water and nutrients. The objective of this study was to investigate the potential application of an irrigation schedule based on previously determined threshold values of volumetric substrate water content to improve strawberry (Fragaria ananassa L. cv. ‘Seolhyang’) cultivation in a commercial hydroponic farm. Specifically, we aimed to improve water and fertilizer delivery in a coir substrate hydroponics system using frequency domain reflectometry (FDR) sensor-automated irrigation (FAI). For comparison, a conventional fixed timer-based irrigation (TIMER) treatment was applied. We observed a significant decrease in irrigation volume when strawberry plants were cultivated using FAI due to a reduced drainage ratio, whereas irrigation scheduling using TIMER consumed large amounts of nutrient solution. The weekly irrigation volume per plant for the experimental period averaged 370 mL for the FAI system and 666 mL for TIMER. The weekly drainage volume per plant averaged 55.8 mL for the FAI system and 300 mL for TIMER. The total irrigation volume for TIMER was 1.7-fold higher than that for FAI, while there was no significant difference in the total retained volume in the substrate between the two treatments during the experimental period, which led to a 1.2-fold higher WUE under FAI. Plant growth, fruit yield, and soluble solid content did not significantly differ between irrigation methods. The volumetric water contents in the substrate ranged from 58 to 62% and from 63 to 65% for FAI and TIMER, respectively. The EC level of the substrate solution (measured using an FDR sensor) ranged from 0.8 dS·m -1 to 1.4 dS·m -1 for both the FAI and TIMER systems. A cost savings of approximately 41% (for fertilizer) was achieved in FAI compared to TIMER. The FAI technique for coir substrate hydroponics can be utilized in large-scale hydroponic farms, resulting in the efficient and environmentally sustainable use of water and fertilizer.