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- Author or Editor: Richard C. Beeson Jr x
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.
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.
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.
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.
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.
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.
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.
Rain drop momentum, based on the height from which it falls, is an important factor in drop penetration of plant canopy. This may explain why nursery operators report that substrates appear wetter from rain than from an equivalent amount of water applied with overhead irrigation. We investigated the influence of irrigation nozzle height on amount of water captured by Rhododendron sp. `Formosa' grown in 10-liter containers. A Wobbler® (#8, 7.6 liters·min–1) irrigation nozzle was positioned 1.2, 2.4, 3.6, 4.8, or 6.0 m above grade. Plants were placed in a circle 3.6 m from the riser base for the 1.2-m-high nozzle, 4.5 m from riser base for the 2.4-m-high nozzle, and 5.4 m from riser base for all other heights and irrigated for 3 hours. Preweighed disposable diapers were placed on substrate surface of each container with and without (control) plants. Diapers were weighed after irrigation and water captured was calculated and expressed as percentage of control containers. Capture increased from 144% at 1.2 m to 178% at 3.6 m then declined with increasing height. The decline was likely due to small drops with low momentum striking plants because plants remained 5.4 m from the riser base.
Marketable size plants of sweet viburnum (Viburnum odoratissimum Ker-Gawl.), waxleaf ligustrum (Ligustrum japonicum Thunb.), and azalea (Rhododendron spp. L. `Southern Charm') grown in 11.4-L containers were irrigated with overhead impact sprinklers at container spacings ranging from 0 to 51 cm apart. Water reaching the substrate surface was quantified and the percentage of that applied calculated as percent capture (% capture). Percent capture is defined as the percentage of water falling above the plant within a projected vertical cylinder of a container that reaches the substrate surface. For all species, % capture increased linearly with the decline in adjacent canopy interaction, which results from canopies extending beyond the diameter of a container. Increases in total leaf area or leaf area outside the cylinder of a container, in conjunction with increasing distance between containers, were significantly (P < 0.05) correlated with increases in % capture for ligustrum and viburnum. Increases in % capture partially compensated for decreases in percentage of production area occupied by viburnum containers as distances between containers increased, but not for the other two species. Under commercial conditions, optimal irrigation efficiency would be achieved when plants are grown at the minimum spacing required for commercial quality. This spacing should not extend beyond the point where canopies become isolated.
Petunia `Midnight' were grown in drainage lysimeters in an open-sided clear polyethylene covered shelter to evaluate growth responses in response to alternative irrigation strategies. Three irrigation methods were evaluated: tensiometer-controlled automatic irrigation system, regularly scheduled irrigation utilizing an automated controller, and human perception of plant irrigation need. Drainage lysimeters (250 L) were backfilled with native sand field soil to simulate landscape conditions and managed with Best Management Practices. Following establishment, lysimeters irrigated by an automated controller were irrigated 1.3 cm daily. Tensiometer-controlled lysimeters were irrigated when plant available water (2.5 kPa to 1.5 MPa) had declined to 70% or less, and were irrigated back to field capacity. Canopy growth indices and leaf gas exchange measurements were evaluated relative to irrigation strategies. Actual evapotranspiration was calculated for each replication. Daily irrigation resulted in significantly higher assimilation rates, transpiration rates, and final shoot dry weights than the other treatments tested. Assimilation rates and transpiration rates were significantly higher for tensiometer-controlled irrigation than the human judged treatment, but no differences were found in final shoot dry mass.