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  • Author or Editor: Lucas O’Meara x
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As a result of the lack of quantitative data regarding specific water requirements of ornamental species, precision irrigation can be a difficult task for nursery growers. One challenge for growers is that it is not clear how much of the water in soilless substrates is actually available for plant uptake. Substrate moisture release curves (MRC) have been used to predict the amount of plant-available water in soilless substrates, yet there is little information about whether there are differences among species in their ability to extract water from substrates. The objectives of this study were to determine 1) the hydraulic properties of a composted pine bark substrate; and 2) how water uptake in Hydrangea macrophylla and Gardenia jasminoides was affected by decreasing substrate volumetric water content (VWC). As the substrate VWC decreased from 0.38 to 0.17 m3·m−3, substrate matric potential decreased from –4.0 to –69 kPa, whereas hydraulic conductivity decreased from 0.115 to 0.000069 cm·d−1. To measure plant water uptake in a drying substrate, growth chambers were used to provide stable environmental conditions that included continuous lighting to prevent diurnal fluctuations in water use. Water use by H. macrophylla ‘Fasan’ started to decrease at a higher VWC (0.28 m3·m−3) than G. jasminoides ‘Radicans’ (0.20 m3·m−3). Plant water uptake stopped at a VWC of 0.16 m3·m−3 in H. macrophylla and 0.12 m3·m−3 in G. jasminoides. The results show that H. macrophylla is less adept at extracting water from a drying substrate than G. jasminoides. Traditionally, plant-available water in soilless substrates has been studied using substrate MRCs. Our data suggest that substrate hydraulic conductivity may be an important factor controlling water availability to the plants. In addition, there are important differences among species that cannot be detected by only looking at substrate hydraulic properties.

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Irrigation is an essential component of ornamental plant production, yet relatively little is known about how much water nursery crops require to maintain optimal growth rates. Our objectives were to precisely determine the daily water use (DWU) of Hydrangea macrophylla and Gardenia jasminoides grown in 6-L containers, quantify how this is affected by environmental conditions, develop a quantitative model describing DWU, evaluate this model with an independent data set, and determine the feasibility of using crop coefficients (Kc) for irrigation scheduling. In 2010, we quantified the DWU of two Hydrangea macrophylla cultivars, Fasan and Pia. There was little difference in DWU of the two cultivars, which ranged from 50 to 300 mL/plant/day depending on plant age and environmental (hoophouse) conditions. In 2010, daily light integral (DLI) had the greatest influence on DWU with DWU increasing with increasing DLI. The combination of plant age, final leaf area, DLI, and their interactions explained 83.2% and 90.8% of day-to-day variation in DWU of ‘Fasan’ and ‘Pia’, respectively. In July 2011, a follow-up study was conducted using Hydrangea macrophylla ‘Fasan’ and Gardenia jasminoides ‘Radicans’. DWU of ‘Fasan’ ranged from 50 to 200 mL/plant/day and DWU of ‘Radicans’ ranged from 50 to 560 mL/plant/day. The lower DWU of ‘Fasan’ in 2011 compared with 2010 was the result of stunted growth of the hydrangeas, a result of elevated temperatures within the hoophouse during the plants initial growth flush. Vapor pressure deficit (VPD) explained more of the daily fluctuations in DWU in 2011 compared with 2010. Predicting DWU of the 2011 ‘Fasan’ crop using 2011 environmental conditions and the model developed using the 2010 data resulted in DWU estimates that were on average 64% too high. This discrepancy is likely the result of slower overall growth rate and a 15.4% reduction in ‘Fasan’ total growth in 2011 compared with 2010 and points to the challenges of modeling DWU. There were distinct seasonal changes in Kc values for the crops, but the trends differed between 2010 and 2011. Our results suggest that an accurate measure of canopy size may improve performance of predictive water use models.

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