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Hui-lian Xu, Jean Caron, and André Gosselin

Water potential at soil–root interface (ψ s-r) indicates soil water availability to the plants. It is related to plant water potential and transpiration. To know the characteristics of ψ s-r, in the plants under a subirrigation system, hysteresis of ψ s-r, as well as xylem water potential (ψ x) and transpiration were examined in response to soil dehydration for Prunus × cistena grown in three soil mixes: mix 1-composted bark, peat, and sand; mix 2—peat, bark, sand, and compost; and mix 3—peat, sawdust, and sand. When the soil mixes were dried from high to low water potential (ψ s), plants grown in mix 2 maintained higher ψ s-r, as well as higher ψ x and higher transpiration. However, when the soil mixes were dehydrated from the bottom, the relationships of ψ s-r, ψ x, and transpiration to ψ s showed strong hysteresis effect. ψ s-r was always lower at a given ψ s when soil was rewetted from dry to wet conditions than when soil was dried from wet conditions. ψ x and transpiration also showed hysteresis in response to soil dehydration. The extent of hysteresis was the largest in mix 2 and the smallest in mix 3. Hysteresis of ψ X or transpiration showed a similar trend to that of ψ s-r. This suggests that ψ s-r is a good indicator of soil water availability to the plants and more directly related to ψ X and transpiration than is ψ s. The difference in hysteresis of ψ s-r among soil mixes might be related to the properties of hydraulic conductance, which are determined by the soil texture. Hence, further study is needed to elucidate the mechanism of the hysteresis phenomenon.

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Anthony V. LeBude*, Barry Goldfarb, and Frank A. Blazich

Producing high quality rooted stem cuttings on a large scale requires precise management of the rooting environment. This study was conducted to investigate the effect of the rooting environment on adventitious root formation of stem cuttings of loblolly pine (Pinus taeda L.). Hardwood stem cuttings of loblolly pine were collected in Feb. 2002 from hedged stock plants and stored at 4 °C until setting in Apr. 2002. One hundred stem cuttings per plot in each of two replications received 45, 61, 73, 102, 147, or 310 mL·m-2 of mist delivered intermittently by a traveling gantry (boom) system. Mist frequency was similar for all treatments and was related inversely to relative humidity (RH) within the polyethylene covered greenhouse. Rooting tubs in each plot were filled with a substrate of fine silica sand, and substrate water potential was held constant using soil tensiometers that activated a subirrigation system. Cutting water potential was measured destructively on two cuttings per plot beginning at 0500 hr every 3 hh until 2300 hr (seven measurements) 7, 14, 21, or 28 days after setting. During rooting, leaf temperature and RH were recorded in each plot to calculate vapor pressure deficit (VPD). Cutting water potential and VPD were strongly related to mist application. Cutting water potential was also related to VPD. Rooting percentage had a linear and quadratic relationship with mean cutting water potential and VPD averaged between 1000 and 1800 HR. Eighty percent rooting occurred within a range of values for VPD. Data suggest that VPD can be used to manage the water deficit of stem cuttings of loblolly pine to increase rooting percentage. These results may be applicable to other species and to other rooting environments.

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L.T. Case, H.M. Mathers, and A.F. Senesac

Container production has increased rapidly in many parts of the U.S. over the past 15 years. Container production has been the fastest growing sector in the nursery industry and the growth is expected to continue. Weed growth in container-grown nursery stock is a particularly serious problem, because the nutrients, air, and water available are limited to the volume of the container. The extent of damage caused by weeds is often underestimated and effective control is essential. Various researchers have found that as little as one weed in a small (1 gal) pot affects the growth of a crop. However, even if weeds did not reduce growth, a container plant with weeds is a less marketable product than a weed-free product. Managing weeds in a container nursery involves eliminating weeds and preventing their spread in the nursery, and this usually requires chemical controls. However, chemical controls should never be the only management tools implemented. Maximizing cultural and mechanical controls through proper sanitation and hand weeding are two important means to prevent the spread and regeneration of troublesome weeds. Cultural controls include mulching, irrigation methods (subirrigation), and mix type. Nursery growers estimate that they spend $500 to $4000/acre of containers for manual removal of weeds, depending on weed species being removed. Economic losses due to weed infestations have been estimated at approximately $7000/acre. Reduction of this expense with improved weed control methodologies and understanding weed control would have a significant impact on the industry. Problems associated with herbicide use in container production include proper calibration, herbicide runoff concerns from plastic or gravel (especially when chemicals fall between containers) and the need for multiple applications. As with other crops, off-site movement of pesticides through herbicide leaching, runoff, spray drift, and non-uniformity of application are concerns facing nursery growers. This article reviews some current weed control methods, problems associated with these methods, and possible strategies that could be useful for container nursery growers.

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Myung Min Oh, Young Yeol Cho, Kee Sung Kim, and Jung Eek Son

Subirrigation, such as the ebb-and-flow culture (EBB) system, is a popular method in containerized plant production for controlling the application of fertilizer, water, and pesticides, and for improving production efficiency ( Dole et al., 1994

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Subirrigation in the Greenhouse Industry Subirrigation promotes high-quality plant production with minimal environmental impact since it reuses the nutrient solution. Most subirrigation systems apply the water to waterproof ebb-and-flow benches or

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Craig D. Stanley and Gurpal Toor

reduce the potential for water and nutrient use efficiency ( Smajstrla et al., 2002c ). Irrigation methods for horticultural crop production in Florida consist of subirrigation (seepage) using water table management, drip irrigation, microsprinkler, and

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Not Effect Bee Balm Growth Paclobutrazol, uniconazole, or flurprimidol were applied to bee balm at several concentrations as a substrate drench or through subirrigation. Pepin and Cole (p. 313) found that substrate drench applications were more

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Daniel Leskovar and Yahia Othman

media in the cells of the tray ( Liu et al., 2012 ) and reduce transplant quality. Since there is little runoff from the growing medium when FL or subirrigation is used, a recommended fertilizer guideline is to reduce fertilizer (20N–10P–20K

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containers, but little research has been conducted on long-term crops grown in these containers in subirrigation systems. Beeks and Evans (p. 173) found that cyclamen plants could be successfully grown in a subirrigation system by switching from plastic

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Roland Ebel

capillarity conducts water from the canals to the crops in an “integrated” sub-irrigation system ( Renard et al., 2012 ). Only very particular soil and plant properties allow natural sub-irrigation. The width and height of the wetland fields as well as the