110 the tree establishment period at its new site. Regular and frequent watering is commonly recommended in most tree planting guides, especially during the first several months after transplanting (Lipkis 1990; Gil- man 2002; Starbuck, 2006). Because a water source may not be available near a tree planting site, water may have to be hauled to the tree planting site several times per week. However, frequent watering, either by hand or by machines, can be time consuming and expensive, so this practice may not be optimal for tree planting projects in the urban landscape. An inexpen- sive watering method would be to install a device around the stem that can deliver water more slowly over a longer time period. Whatever the method being employed, slow watering is necessary to maximize infiltration through the soil profile and to minimize sur- face water runoff, thereby encouraging deep root growth and tree establishment. Reduced surface runoff also helps conserve water in the landscape. Several types of watering devices are available to aid in tree watering, such as upright bags, ring bags, and tubs, which can typically hold 19 to 95 liters of water (depending on device design). For this study, the term “indirect watering devices” was used because water is delivered to the tree via a container with small holes at the bottom and not directly from a hose or poured bucket (direct watering). Other descriptions for these types of devices include pas- sive watering, drip irrigation, slow-release or slow drip, and root feeder. These devices have the advan- tage of being filled up quickly and then releasing water either slowly but deeply to the tree roots over time, or directly to the root zone, both with the intended purpose of reducing water stress and facili- tating successful transplanting. Furthermore, these devices are cost-effective and light in weight, allow- ing them to be readily installed around a tree. Despite these advantages, we are unaware of any studies that have compared different watering devices quantita- tively to determine which device benefits the tree most in terms of decreasing water stress and increas- ing tree growth. Although there is one study that has compared watering systems for newly planted trees, the comparison was qualitative (e.g., rank scoring) rather than quantitative (Beginners Guide for Water- ing New Trees 2014), hence providing only subjec- tive information for tree planters. The purpose of this study was to evaluate and compare three different types of devices used to water ©2019 International Society of Arboriculture Hossain et al: A Comparison of Indirect Watering Devices newly transplanted river birch (Betula nigra) trees in a controlled greenhouse environment. In particular, the objectives of this study were to: 1) evaluate per- formance of indirect tree watering devices in terms of device characteristics and water delivery; and 2) compare watering devices to determine which device type has the most potential to benefit the tree in terms of reducing water stress and enhancing growth. We designed this study to simulate the use of indirect watering devices on newly transplanted trees in the urban landscape. Experiments were conducted in a greenhouse with container-grown trees in order to control for variations associated with natural precipi- tation, temperature, and soil. River birch was chosen as a candidate species for this study mainly because it tends to show water stress more readily than other species. Furthermore, river birch trees are relatively site-adaptable and aesthetically pleasing (color and appearance of bark and fall leaves), rendering them suitable for urban planting. MATERIALS AND METHODS Site This study was conducted in a temperature-controlled greenhouse on the University of Arkansas at Monti- cello campus located in southeast Arkansas, U.S.A. Watering Devices Watering devices used in this study were flexible bags or rigid tubs that hold a given amount of water which is slowly released over time to the tree roots though holes in or near the bottom of the device. We examined two examples of each of the three com- monly available types of slow-release watering devices: 1) upright bags (Treegator® and ArborRain® (Figure 1, panels 1 and 2); 2) ring bags (Treegator® Pro and ArborRain® 3) open tubs (Tree I.V.® (Figure 1, panels 5 and 6). ) Jr. ) (Figure 1, panels 3 and 4); and and Bioplex® Tree Ring Jr.) The actual water holding capacity for the two upright bags (ranged from 58.7 to 62.5 liters) and the Tree I.V. tub (19 liters) was the same as rated (ranged from 19 to 75 liters), but less than rated for the two ring bags (ranged from 47.3 to 49.2 liters for the Tree- gator Jr. Pro and from 64.4 to 66.2 liters for the Arbor- Rain). The Bioplex tub’s actual capacity was 33.1 liters. This capacity discrepancy for the Bioplex tub necessitated adjustments of water volume for that tub
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