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Two sensor-based irrigation scheduling systems were compared for water use and plant growth in container-grown Green Velvet boxwood (Buxus sempervirens L. × B. microphylla Siebold & Zucc. var. koreana ‘Green Velvet’) and slender deutzia (Deutzia gracilis Siebold & Zucc). These crops were chosen because they have different water requirements during production. The two sensor-based irrigation systems included a physiological-based on-demand (OD) irrigation system where the set point was derived from the relationship between substrate moisture and photosynthetic rate. The second system was a daily water use (DWU) method where the amount of water used by the crop was replaced each day. The objective of the study was to evaluate and compare water use and growth metrics using the OD and DWU irrigation scheduling regimes for two container-grown woody plants that differed in their water consumption. There were no differences in root and shoot biomass or growth index due to the irrigation schedule employed for either boxwood or deutzia. For boxwood plants, OD irrigation reduced water consumption by 35.5% and enhanced water use efficiency (WUE) by 54.5% compared with DWU. Total water use of deutzia in OD zones was reduced by 26.5% compared with DWU. DWU offers the labor scheduling advantage of irrigation occurring at a set time of day, and OD offers the advantage of watering as required, potentially reducing water stress as the season progresses and as the plant size and atmospheric demand increase.

An experiment was conducted to determine which of five substrate-moisture sensor placements best estimates volumetric water content (VWC) for 11.4 L containers filled with Hibiscus moscheutos ‘Pink Elephant,’ as well as the effect of low VWC on sensor measurements. Five sensor placements were tested; three sensors were horizontally inserted into the sidewall at 5, 10, and 15 cm from the base of the container and the other two placements were inserted into the substrate surface either vertically or diagonally. All positions showed a strong linear relationship (r2> 0.92) with VWC determined gravimetrically, indicating they all are appropriate models of container substrate moisture. Sensors placed 15 cm above the base had a y-intercept closer to zero than sensors at 5 cm from the base, vertical and diagonal, but the slope was less accurate (farther from 1, P-value 0.0148) than the vertical placement. Vertical placement had a more accurate slope than 15 cm from the base, but the y-intercept was further from zero. The substrate was dried to 0.11 m3·m-3 during the experiments and became hydrophobic. This substantially decreased the amount of water that could be held at effective container capacity and decreased sensor accuracy. For this species and container size, no probe placement proved superior to the other placements, but choosing a horizontal placement was most practical for pesticide applications, pruning and hand weeding while surface installed placements may be most practical for sensor calibration and ease of installation, and removal.

a b s t r a c t Independently controlled irrigation plots were designed to test two container nursery irrigation regimes on oakleaf hydrangea (Hydrangea quercifolia 'Alice') in both nursery and controlled greenhouse environ- ments. The experiments were conducted in both 3.8 and 11.4 L containers. Plants were automatically irrigated by one of two soil moisture sensor-based regimes: (1) a daily water use (DWU) system that delivered the exact amount of water that had been lost in the previous 24 h and (2) an on-demand (OD) irrigation system based on a specific substrate moisture content derived from the relationship between substrate moisture and photosynthetic rate. In this system, irrigation was applied when the substrate

Genetic engineering of nitrogen assimilation has received considerable attention for its improvement of nitrogen use efficiency in crops. Overexpression of maize Dof1 (ZmDof1), a plant-specific transcription factor, has been reported to promote nitrogen assimilation and growth under low-nitrogen conditions in transgenic Arabidopsis and rice. The present study explored its application in Populus by overexpressing the ZmDof1 gene. Contrary to the results in Arabidopsis and rice, introduction of the ZmDof1 gene did not improve growth of transgenic Populus under different low-nitrogen conditions both in vitro and in greenhouse. Expressions of genes that are involved in nitrogen assimilation and carbon fixation were not induced in ZmDof1-transgenic Populus. Nitrogen/carbon concentrations and photosynthesis rate were not increased in the ZmDof1-transgenic Populus. The results in transgenic Populus overexpressing the ZmDof1 gene indicated that ZmDof1 did not play an important role in nitrogen assimilation under low nitrogen condition in woody Populus plants as it did in annual Arabidopsis and rice plants.

In container nursery production, managing irrigation is critical for reducing agrichemical runoff. Boxwood (Buxus) and deutzia (Deutzia) plants grown in 1-gal and 3-gal containers respectively were conservatively irrigated by one of two substrate moisture sensor (SMS)-based regimes: 1) a daily water use (DWU) system that delivered the exact amount of water that had been lost in the previous 24 h and 2) an on-demand (OD) irrigation system based on a specific substrate moisture content derived from the relationship between substrate moisture and photosynthetic rate. Unfortunately, commercial nurseries have not readily adopted SMS-based irrigation systems partly due to expense and reliability of the sensors. The objective of the present study was to evaluate easily accessible weather variables [light integrals (LI) and vapor pressure deficit (VPD)] as a substitute for substrate moisture sensors to determine water volume applied for the DWU system and to predict timing of irrigation based on OD. Daily irrigation water volume was correlated with daily LI (correlation coefficient, R = 0.68 and 0.63 for boxwood and deutzia, respectively) and less so with accumulated vapor pressure deficit (R= 0.36 and 0.19 for boxwood and deutzia, respectively). The analysis suggested that irrigation should be scheduled following 6,227 W·m-2 for boxwood and 5,880 W·m-2 for deutzia plants.