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  • Author or Editor: Richard C. Beeson Jr x
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In many sectors of agriculture, precision irrigation, applying only what water is needed for a given small area, has become a familiar term. Irrigation in most woody ornamental nurseries, though, has changed little since the 1960s. In many areas of the U.S., irrigation volumes required for nursery production have come under scrutiny due to projected, or real, competition for water with urban populations, or concerns over nursery runoff. Modeling of woody ornamental water use, and subsequent irrigation requirements, has been limited and focused mostly on trees. Previous research for modeling of non-tree water use is reviewed as an introduction to current efforts to develop models for precision irrigation of woody ornamentals. Pitfalls and limitations in current modeling efforts, along with suggestions for standardizing future research is emphasized. The latest model derived from recent research is presented.

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Transpiration of woody shrubs appears to increase with decreases in plant density within production beds as plants are randomly removed for sale. To assess potential impact on irrigation management, this observation was tested with market-sized plants in suspension lysimeters at specific levels of canopy closure. Canopy closure was defined as the percentage of cumulative projected two-dimensional canopy area of individual plants per unit ground area on which they were placed. In 1997, evapotranspiration (ETA) of plants in 26.6-L containers was comparable from isolated plants up to 67% canopy closure. At full canopy closure (100%), ETA was 40% less than 67% closure or lower. When repeated in 2003, results were similar for similar-sized plants and for two sizes smaller (11.4- and 3.8-L containers). ETA response to canopy closure was independent of height from 0.5 to 1.5 m tall. At full canopy closure, whole plant transpiration was equivalent to that measured from only the upper 40% (by height) of the canopy under full sun. This was independent of plant size. Implications for water conservation during production and plants’ irrigation needs in landscapes are discussed.

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Rooted cuttings of Viburnum odoratissimum were grown outdoors to market size in 11.4-L containers. Actual evapotranspiration (ETA) of nine plants was determined daily as was evaporation from three control containers shaded with plastic foliage to mimic plant growth. The first 60 d after transplanting, substrate evaporation accounted for most of ETA. Substrate evaporation was generally constant the first 160 days before declining, but still remained ≈160 mL/day through harvest at market size. ETA increased with growth and generally followed variations in reference evapotranspiration (ETo). Mean ETA during most of the production cycle was less than 600 mL/day (11.8 mm based on upper container surface area). With the spring growth flush, mean ETA reached 1.3 L/day as plants achieved market size. Mean cumulative ETA to produce 90% of measured plants to market size was 155 L or 3.1-m depth per plant based on container surface area. Water need indices, similar to crop coefficients, were highly correlated with percent canopy closure (%Closure) using an exponential decay equation. When overlain with previous similar data for Ligustrum japonicum, the correlation for the combined data set had an r 2 = 0.843. This suggests that the %Closure model may provide a method for ETo-based irrigation of woody shrub species based on canopy size and spacing.

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Municipal Solid Waste (MSW) compost was evaluated as a component of landscape ornamental container media to reduce irrigation requirements and identify beneficial uses of the material. MSW compost was blended at 10 to 40% by volume with pine bank and coarse sand. Three landscape ornamentals were produced to marketable 10 liter-size plants in each medium during an 18-month production period. Twenty percent MSW compost produced similar shoot and root growth to the “standard” medium consisting of 20% Florida sledge peat. Thirty or 40% MSW compost inhibited root growth to the lower depths of a container during the rainy summer months. This inhibition was no longer evident after growth during the dry late fall to early spring months. Root growth inhibition was due to decreased aeration rather than phytotoxic leachate. Up to 20% MSW compost can be used for container media in wet climates whereas 40% would produce high quality plants under dry climates.

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Pulsing consists of applying subvolumes of a normal daily irrigation volume several times per day. Previous studies have shown splitting overhead irrigation into two subapplications increased growth of container-grown landscape ornamentals in the southeastern U.S. In Florida, water restrictions prohibit overhead irrigation during the critical mid-afternoon when irrigation is most beneficial. Using individual microirrigation spray stakes, only 25% of the water required for overhead irrigation per bed area was necessary to produce similar plants if irrigated once per day. When the same daily volume was pulsed as 2 or 3 subvolumes, tree growth was significantly increased. Data suggest 2 pulses are sufficient for trees with a xeric nature while mesic trees prefer 3 pulses per day. Root:shoot ratios were unchanged by pulsing. Lower cumulative diurnal water stress was measured on pulsed trees.

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Rooted cuttings of Rhaphiolepis indica, a low slow-growing evergreen shrub, were grown outdoors in weighing lysimeters to market size in 11.4-L containers. Actual evapotranspiration (ETA) and evaporation from containers shaded with plastic foliage was determined daily. The first 60 days after transplanting, substrate evaporation accounted for most of ETA and was the major component through the first 127 days. ETA generally followed variations in reference evapotranspiration (ETo). Mean cumulative ETA to produce 90% of measured plants to market size was 101 L or 1.99-m depth per plant based on container surface area. Water need indices, similar to crop coefficients, were highly correlated with percent canopy closure using an exponential decay equation (r 2 = 0.898), but a more precise estimate at higher canopy closures was achieved using a third-order inverse polynomial equation (r 2 = 0.907). When combined with similar previous data from Viburnum odoratissimum and Ligustrum japonicum, the inverse polynomial equation correlation was 0.802 for all three shrubs. This implies the %Closure model provides a good general base for ETo-based irrigation of woody evergreen shrub species based on canopy size and spacing with improved precision when individual equations are derived by species.

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Bromeliads are important ornamental foliage plants, but until now, their daily water use during production was unknown. Using a canopy closure model developed for container-grown woody ornamental plants, in this study we investigated actual evapotranspiration (ETA) of Guzmania ‘Irene’ and Vriesea ‘Carly’ from tissue-cultured liners grown in 15-cm containers to marketable sizes in a shaded greenhouse. The mean daily ETA of Guzmania ‘Irene’ ranged from 4.02 to 66.35 mL per plant, and the mean cumulative ETA was 16.66 L over a 95-week production period. The mean daily ETA of Vriesea ‘Carly’ varied from 3.98 to 59.89 mL per plant, and the mean cumulative ETA was 15.52 L over the same production period as the Guzmania cultivar. The best-fit models for predicting daily ETA of the two bromeliads were developed, which had correlation coefficients (r 2) of 0.79 for Guzmania ‘Irene’ and 0.68 for Vriesea ‘Carly’. The success in the model of ETA for both bromeliads suggested that the canopy closure model was equally applicable to container-grown ornamental foliage plants produced in greenhouse conditions. The daily ETA and cumulative ETA values represent research-based information on water requirements, and, when applied, could improve irrigation practices in bromeliad production. This study also showed that roots per se of the two epiphytic bromeliads were able to absorb water and nutrients from a peat-based container substrate and support their complete life cycles.

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Abstract

Needle starch metabolism was studied during graft development of Colorado blue spruce (Picea pungens Englemann ‘Hoopsi’) scions on Norway spruce [Picea abies (L.) Karst] rootstocks. Starch accumulated during the initial stages of union formation, but the rate of accumulation slowed over time. Peak starch content in developing greenhouse grafts was ≈30% and, in lath house grafts, ≈50% of that in 3-year-old grafts forced in the greenhouse. Prior to budbreak, starch content declined rapidly, stabilizing at pre-grafting levels during shoot elongation. Grafts with misaligned unions accumulated starch during the first week, but the starch content then declined. Preventing photosynthesis in scions during union formation prevented starch accumulation, but did not affect graft success or subsequent scion growth. We concluded that neither starch accumulation nor current photosynthesis in the scion were required during union development.

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Abstract

The study evaluated the roles of storage carbohydrates and neutral lipids in the success of Colorado blue spruce (Picea pungens Englemann ‘Hoopsi’) grafts. These scions do not require photosynthesis nor receive photosynthates from the rootstock during union development. Carbohydrate and neutral lipid contents, along with respiration and scion water relations, were measured during union development. Stored carbon compounds were sufficient to supply the needs of the scion during the 9 weeks of union development. Estimates of carbohydrate use indicated that decreases in sugar content (bark and needle) were insufficient to account for more than 25% of the estimated respiration. The results indicate that the quantity of carbon storage compounds is not a factor in graft success. We propose that neutral lipids may be the major carbon reserve of the scion during graft formation.

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Previous research indicated that bedding plants can be maintained in landscape soils allowed to dry to substantially less than field capacity before irrigation; however, canopy size and aesthetic quality were compromised. Continuing this research, ‘Yalaha’ coleus (Solenostemon scutellarioides) were grown in drainage lysimeters in an open-sided clear polyethylene-covered shelter and a companion uncovered field plot to assess growth characteristics and landscape quality when irrigated at various managed allowable deficits. Using tensiometers, plants were irrigated back to field capacity when plant-available water within a soil was depleted to 70% or 50%. Deficits were evaluated against a control treatment of 0.5 inch daily irrigation. Total irrigation volume applied was significantly greater for the control treatments than deficit irrigation treatments. The net result was 78% and 90% average reductions in total volume applied to lysimeter and field-grown coleus respectively. On average, height was 20% and 15% greater for well-watered controls grown in lysimeters and field plots respectively than plants grown in deficit irrigations. Canopy size of nondeficit controls was 26% and 72% greater on average than deficit treatments in lysimeter and field plots respectively. However, shoot and root dry weights, total biomass, shoot-to-root ratios, and landscape quality were similar among treatments for both locations.

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