Soil moisture sensor-based automated irrigation of Cymbidium under various substrate conditions

Abstract Most orchid growers use bark as substrate to avoid too wet conditions, although it requires excessive water use of leaching. We conducted research to investigate the applicability of a soil moisture sensor-based automated irrigation system in Cymbidium production for efficient irrigation management and compared the growth and water use of Cymbidium under various substrate conditions. One-year-old Cymbidium ‘Hoshino Shizuku’ plantlets were grown in bark, coconut husk chips, coir dust, or a commercial growing mix at a similar matric potential within the easily available water range. Irrigation occurred when the substrate dried below the volumetric water content thresholds at 0.25, 0.30, 0.35, and 0.40 m3 m−3 in the bark, coconut husk chips, coir dust, and the commercial growing mix, respectively. Pseudobulb size, net photosynthetic assimilation rate, fresh shoot, and root weight of the Cymbidium showed no differences among the substrates, although Cymbidium grown in the commercial growing mix had better shoot growth than plants in the other substrates. The amount of irrigation was higher (ca. 6 times) in coarse substrates (bark and coconut husk chips) than fine substrates (coir dust and the commercial growing mix), indicating that fine substrates with higher water-holding capacity could use water more efficiently. The amount of irrigation and nutrient availability of the substrate in the coarse substrates were much lower than those in the fine substrates, producing a difference in growth of the Cymbidium among the substrates. Water use efficiency was 8–9.5 times higher in Cymbidium grown in fine substrates than plants grown in coarse substrates. Overall, the soil moisture sensor-based automated irrigation system could provide an appropriate moisture level for Cymbidium grown in fine substrates, avoiding too wet conditions, and produced quality Cymbidium with more efficient water and nutrient use than orchids produced in coarse substrates.