2018 ASHS Annual Conference

The effect of reducing substrate moisture availability on the growth of two yellow garden mum (Chrysanthemum morifolium) cultivars (Chelsea and Ursula) was investigated in a greenhouse study. Seedling of both cultivars were transplanted and grown into 8-inch pots filled with two soilless substrates – Sunshine Gro mix- LC1 (70% peat moss:30% perlite) and a wood fiber (WF) substrate (60% peat moss:40% wood fiber). The experiment was laid out in randomized complete block design with four replications and consisted of three irrigation treatments. Moisture release curve for the substrates used in the study was developed using the Hyprop device (METER Group Inc., Pullman, WA). Based on the volumetric water content (VWC) vs. matric potential (MP) relationship observed, three VWC values (45% - Control, 35% - IT1 and 25%-IT2) were selected as set-points for treatments in order to apply progressively less irrigation water. VWC and MP measurements were obtained with GS-1 and MPS-6 sensors (METER Group Inc.) on a 5-min basis using Em50R data loggers (Meter Group Inc.,). Recorded data was transmitted through a basestation to Sensorweb^TM software (Mayim LLC., Pittsburgh, PA). For each substrate, VWC readings from two plants (one from each cultivar) in each experimental unit were averaged on a 15-min basis. Irrigation was applied for 15-sec durations whenever the average VWC sensed was below the corresponding set-point using PlantPoint^TM (METER Group Inc.) control data loggers that were connected to solenoid valves. The substrate VWC for each substrate was maintained within a very narrow range of the set-points throughout the study. Irrigation application was recorded with flowmeters (Model 25, Badger Meter Inc., Milwaukee, WI). Plants were destructively harvested at full maturity and data on growth index (GI), leaf area (LA), leaf fresh mass (LFM), leaf dry mass (LDM), flower number (FN), flower fresh mass (FFM), flower dry mass (FDM), stem fresh mass (SFM), stem dry mass (SDM), total shoot mass (TSM) and root dry mass (RDM) were obtained. Analysis of harvest data showed that there were no significant differences between irrigation treatments for all measured parameters for cv. Chelsea in the WF substrate. However, significant differences in the parameters GI, LA, LFM, FFM, FN, SFM, SDM, TSM and RDM were observed for cv. Ursula, with the IT1 and IT2 treatments resulting in plants with less vigor. Irrigation application volume was 16.6% and 41.1% less for the IT1 and IT2 treatments compared to the control. In the LC1 substrate, only GI and FN were significantly different between irrigation treatments for cv. Chelsea; whereas only GI was significantly different between irrigation treatments for cv. Ursula. Volume of irrigation water applied was 33.0% and 33.7% lower for the IT1 and IT2 treatments as compared to the control. The results observed indicate differences in the moisture release properties of the two substrates and possible differences in drought resistance of the two cultivars.