Vegetative Growth and Root Morphology in Cymbidium under Different Substrate Water Content Using a Sensor-based Irrigation System

Abstract

This study was conducted to investigate the optimum substrate volumetric water content (VWC, v/v) of Cymbidium (Exp. 1), and to understand Cymbidium response to water, and morphological characteristics of roots (Exp. 2). One-year-old Cymbidium Yang Guifei plants were cultivated in an experimental greenhouse for 28 weeks. Four different set points, 0.1, 0.2, 0.3, and 0.4 m3·m–3, of coir dust-filled containers were used. VWC were measured by using soil moisture sensors every 20 min, and 32 mL of water was supplied whenever the level was less than each set of points. During the experiment, approximately 25.6, 58.0, 213.4, and 352.8 mL·d–1 of water was applied by sensor-based irrigation system at VWC of 0.1, 0.2, 0.3, and 0.4 m3·m–3, respectively. The 0.1 m3·m–3 was too dry to Cymbidium to grow, because most of them wilted during the experiment. The diameter of mother bulb under 0.3 (37.0 mm) and 0.4 m3·m–3 (39.2 mm) treatment were biggest, while the bulb under 0.2 m3·m–3 (33.4 mm) was decreased due to withering symptoms. In the lead bulb plants, the pseudobulbs under 0.3 and 0.4 m3·m–3 showed the highest growth rate in diameter (27.6 and 26.6 mm), leaf length (57.9 and 56.4 cm), and the number of leaves (15.3 and 13.9), while 0.2 m3·m–3 showed the lowest growth rate, 24.0 mm, 51.5 cm, and 12.5, respectively. Contrary to the growth parameters, the 0.3 m3·m–3 treatment showed the highest rate in light response curve. There was no significant difference in maximum quantum efficiencies (0.79–0.81) of photosystem II (Fv/Fm) of leaves in mother and lead bulbs. In chemical properties, no significant difference was observed in pH, but EC value decreased with increasing VWC. In Exp. 2, ten-month-old plants as in Exp. 1 were cultivated for 12 weeks with the similar environment of Exp. 1. Deficit (479.6 mL·d–1) or moderate irrigations (5,122 mL·d–1) were employed. All growth parameters from the moderate irrigation treatment were significantly higher than to those from to the deficit irrigation treatment. In the root transverse section, cortex thickness and area increased significantly in the moderate irrigation treatment. Considering water usage and growth, 0.3 m3·m–3 can be recommended as optimum VWC for Cymbidium Yang Guifei cultivation.