In Florida, ornamental nurseries and other agricultural entities have been required to obtain volume-limited permits for irrigation water since 1992. Since then, volumes permitted for nurseries have declined. This project set out to establish maximum annual irrigation quantities for Ligustrum japonicum Thumb. grown in three common container sizes. Plants were scheduled and grown such that every 4 months, beginning 1 Jan., plants 2 months from marketable size would be available to place in suspension lysimeters with accompanying border plants. Once in lysimeters, plant weights were recorded every half-hour for 4 months. At that point, plants were 2 months larger than marketable size, thus averaging marketable size over the 4-month period. Data were collected through six 4-month cycles (2 years), along with daily calculation of reference evapotranspiration and monthly canopy measurements. Irrigation was applied overhead and based on a minimum 30% reduction in plant available water within a container. Daily actual evapotranspiration was used to calculate a water need index for each plant. These water need indices, normalized by different surface areas, will be discussed, along with comparisons of cumulative actual evapotranspiration to irrigation depth applied.
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 r2 = 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.
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.
ng production and in landscapes, woody plants are initially spaced apart to develop to desirable landscape quality. As plants grow and canopies begin to interact, canopies transform from individual isolated canopies to one large, closed canopy system. Changes in individual plant actual evapotranspiration (ETA) during the transitions between isolated and closed canopies are 30% on average. Such changes can have a substantial impact on supplemental irrigation requirements, both decreasing with closure and increasing with random removal of plants from a closed canopy. Data will be presented demonstrating changes in ETA as canopy closure progresses from isolated plants through 33%, 67%, and 100% canopy closure. Concurrent data from plants of marketable size grown in 3.8, 10.4, and 26.6 L containers were used to evaluate effects of canopy vertical thickness, and total canopy height, on the changes in ETA relative to degree of canopy closure. Contributions to ETA at 100% canopy closure and isolated plants from leaves at various depths within a canopy will be discussed.
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.
In nursery production, small root balls are transplanted into larger containers and grown for sale or further transplanting into still larger containers. When a root ball is smaller than a container, the amount of plant-available water (PAW) is initially limited to that of the original root ball. With growth, roots colonize new substrate and thereby increase the volume of water available to a shoot. Because of hydraulic gradients in container substrates, PAW is not linearly proportional to the volume of substrate occupied by roots. To practice precision irrigation in nursery production, it is important to know the extent of PAW and how it changes with growth. A method is detailed that calculates in situ PAW in containers based on changes in actual evapotranspiration while irrigation is withheld. The method is applied under field conditions and requires only daily mass loss measurements and corresponding reference evapotranspiration. An example of how PAW changes during production from rooted cuttings to marketable size plants is provided.
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 (r2 = 0.898), but a more precise estimate at higher canopy closures was achieved using a third-order inverse polynomial equation (r2 = 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 (r2) 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.