Daily Water Use of Antirrhinum majus in Hydroponic Greenhouse Production

We are interested in quantifying daily water use for cut-flower Antirrhum majus (snapdragon) production, since floral development is highly sensitive to available water in soilless substrates and plant densities are typically very high in greenhouse cut-flower production. Daily water use of snapdragon cultivars was measured using a load-cell based system coupled with a dense environmental sensor network, including capacitance sensors, temperature and relative humidity, and light (PPF) sensors. Two snapdragon cultivars, ‘Opus Fresh White’ (Group III-IV) and ‘Overture White’ (Group II) were used to estimate daily water use for summer and winter cultivars, respectively. All research was performed in a commercial snapdragon production greenhouse (Bauers Greenhouse, Jarrettsville, MD).  Six replicate bags, each with independent load-cell and sensor systems, were planted with 48 plants per bag. All plants were grown in a perlite (Grade A-20; Pennsylvania Perlite Co., Bethlehem, PA) substrate and fertigated 3–6 times daily with a customized fertilizer solution in a closed hydroponic system.  Substrate water content was maintained at 0.33 ± 0.03 (SD) m³∙m^-3. Plants were grown for 47 and 120 days after transplanting, for the summer and winter cultivars, respectively. All plants were destructively harvested at the end of each study and a number of plant growth variables measured. Leaf area index was measured repeatedly during the studies. Average daily light integrals were very different between seasons (18.3 and 8.0 mol∙m^-2∙d^-1 for summer and winter) but differences in cumulative intercepted light intensity during each production period was relatively small (611 and 709 mol∙m^-2 for summer and winter cultivars). Daily water use of ‘Opus Fresh White’ ranged from 15.1 to 66.9 mL∙d^-1, compared to that of ‘Overture White’ which ranged from 2.6 to 26.2 mL∙d^-1 per plant. The total water use of each cultivar over each production period was similar at 2.0 and 1.9 L per plant for summer and winter, respectively. A daily water use regression model was developed based on plant development and environmental factors. Intercepted daily light integral and vapor pressure deficit accounted for the largest amount of variability in daily water use (P < 0.001). With environmental variables and plant age, a simple daily water use model could provide growers with quick estimate of daily water use, for efficient irrigation scheduling of snapdragon in greenhouse production.