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  • Author or Editor: J.L. Heilman x
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The heat balance method of measuring mass flow of sap was tested on wax leaf ligustrum (Ligustrum japonicum Thunb.) to evaluate its usefulness for measuring water use in shrubs. Sap flow measurements were compared with gravimetric estimates of transpiration in growth chamber and field environments. Sap flow measurements in both environments were within 10% of transpiration, which compared favorably with results reported for herbaceous plants by other researchers. Sizable differences in sap flow, due mainly to differences in leaf area, were found among five plants tested in the field. When flow was expressed on a unit leaf-area basis, differences among plants were greatly reduced. Measurements under partly cloudy skies with fluctuating irradiance showed that changes in sap flow matched those occurring in irradiance.

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A study was conducted to explore how surface materials, including pine bark mulch, bare soil, and turfgrass, affect water use of diverse cultivars (dwarf weeping, dwarf upright, standard weeping, and standard upright) of crape myrtle (Lagerstroemia indica L.). Daily water use was measured gravimetrically, and instantaneous rates of sap flow were measured using heat balance stem flow gauges. Plants of all cultivars surrounded by the mulched surface lost 0.63 to 1.25 kg·m-2·day-1 more water than plants on the soil surface and 0.83 to 1.09 kg·m-2·day-1 more than plants surrounded by turf. The surface temperature of the mulch was higher than that of the other surfaces, resulting in greater fluxes of longwave radiation from the surface. Because of the greater energy load, plants on the mulched surface had higher leaf temperatures and higher leaf-air vapor pressure deficits (VPD) throughout the day. Plants on the mulched area also had higher stomata1 conductances during most of the day compared with those on bare soil and turfgrass surfaces.

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A study was conducted to explore how different mulches affect water use of landscape plants. Plots 4.9 m × 7.3 m, were covered with 5cm pine bark, cypress, white rock, or clay aggregate. 3 potted plants of Ligustrum japonicum (wax-leaf ligustrum) and Photinia × fraseri (red tip photinia) were placed in each plot so that the top of each pot was at ground level. 1 plant of each species was planted directly into each plot. Water loss was measured on a daily basis, both gravimetrically and using heat balance stem flow gauges, during both the 1992 and 1993 growing seasons. Stomatal conductance was measured periodically during each growing season. Surface, air, and soil temperatures at two depths were recorded. During 1992, pine bark mulched plants consistently used more water than the other treatments, as opposed to summer 1993 when the most water was used by plants over white rock. Surface temperatures of pine bark, cypress and clay aggregates were higher than those of white rock both years, by as much as 20C, while temperatures under the mulch varied as much as 5C between pine bark and white rock.

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Foam was applied for frost protection to January planted cantaloupes (Cucumis melo L.) in the Lower Rio Grande Valley of Texas. Two planting configurations consisting of shallow trenches and conventional beds were compared to evaluate volume of foam required and durability. The trench planting technique increased the foam’s durability and reduced the volume approximately three-fourths. The cost of foam application to a low profile crop in the shallow trenches was approximately $74.00 per hectare. Leaf temperature in the foamed trenches was up to 12°C warmer than nonfoamed conventional beds.

Open Access