Water Use Efficiency and Transpiration of Greenhouse Geranium Crop

Zonal geranium (Pelargonium x hortorum 'Real Mintaka') plants were grown in closed soilless systems to evaluate the effect of growing season (winter and spring) on growth, quality, water use, photosynthetic and biomass water use efficiency (WUE) and to calibrate a simplified model for predicting crop transpiration. Photosynthetic WUE was calculated as the ratio between carbon gain in photosynthesis and water loss in transpiration while biomass WUE was calculated as the plant dry biomass divided by the crop water use. The highest maximum air temperature recorded during the first 20 days after transplanting in the spring growing season was presumably responsible for the reduction in shoot biomass production, plant quality, and flowering time of geranium compared to the plants grown in the winter season. The photosynthetic and biomass WUE in the winter (3.1 mg CO2 /g H2O and 4.2 g/L, respectively) season were higher than those recorded during the spring season (2.0 mg CO2 /g H2O and 2.2 g/L, respectively). A multiple linear regression was established between the measured transpiration rates and the radiative and advective terms of the simplified Penman-Monteith equation, taking into consideration only daytime transpiration. The simplified model proposed for predicting short-term rates of transpiration for geranium under our experimental conditions produced a good agreement with measured data.