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C. D. Stanley and G. A. Clark

The use of the recently developed fully-enclosed seepage subirrigation system for fresh market tomato production has demonstrated an improved ability to maintain a water table at a desired level (when compared to conventional ditch-conveyed seepage subirrigation) by means of more precisely controlled application and a greater uniformity throughout the field. This is achieved through use of microirrigation tubing rather than open ditches to convey water to raise the water table to desired levels. When manually controlled, the system has shown to save 30-40% in irrigation amounts primarily due to almost total elimination of surface runoff. An automated control system was designed and evaluated with respect to practicality, durability, and performance of various designs of level-sensing switches. The advantages and limitations of the designs in relation to water table control for tomato production will be presented.

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C.D. Stanley and G.A. Clark

The effect of water table level and fertilizer rates on bell pepper production grown with the fully enclosed subirrigation (FES) system was studied over three fall growing seasons (1992–94). The FES system uses buried microirrigation tubing in the field to convey water for maintaining a water table level and has shown to achieve application savings of 30% to 40% compared to the conventional subirrigation method that maintains a high water table using lateral field ditches. Controlled water table levels of 45, 60, and 75 cm below soil surface and fertilizer rates of 1194, 1716, and 2239 kg·ha–1 (18–0–21 expressed as N–P–K) were used as treatments replicated in time over 3 growing seasons. The 45-cm water table level and 2239 kg·ha–1 fertilizer rate are considered the conventional commercial practices. Results showed that comparable seasonal production levels were achieved among fertilizer rates and water table levels with no significant interactions between treatments. These data indicate that using a lower target water table level allows lower rates of fertilizer to be used because the susceptibility of the fertilizer to leaching caused by excessive rainfall is lessened due to increased soil water storage capacity.

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D.G. Clark and J.W. Kelly

Potted Rosa × hybrida `Meijikatar' plants were produced at 350, 700, and 1050 μl·liter-1 CO2. At a stage of development where half of the flowers showed color, plants were placed into simulated shipping incubators for 5 days at 4 or 16 C.

Increased CO2 levels resulted in shorter production time, increased root dry weight, increased plant height, and reduced total chlorophyll in the upper leaves of the plants. Upon removal from simulated shipping, the number of etiolated shoots per plant increased with increased CO2 concentration. After 5 days in a simulated interior environment, higher shipping temperatures induced more leaf chlorosis, but there were no differences in leaf chlorosis due to CO2 enrichment.

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J.W. Prevatt, G.A. Clark, and C.D. Stanley

Three vegetable irrigation systems, semi-closed subirrigation (seepage), fully enclosed subirrigation (seepage), and drip irrigation, were evaluated for use on sandy soils with naturally high water tables to determine comparative irrigation costs for tomato production. Investment, fixed (ownership), and variable (operating) costs were estimated for each irrigation system. The investment costs of the drip irrigation system were significantly greater than those for the semi-closed and fully enclosed irrigation systems. The variable costs, however, for the semi-closed system were considerably less than those for the fully enclosed and drip irrigation systems. The semi-closed irrigation system, therefore, was determined to be the least-cost tomato irrigation system under present fuel cost and nonlimiting water supply conditions.

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E.E. Albregts, G.A. Clark, C.D. Stanley, F.S. Zazueta, and A.G. Smajstrla

Strawberry (Fragaria ×ananassa Duch.) was grown for two seasons with microirrigation. Preplant fertilizer treatments of zero, one, two, three, and four times the basic N and K rate of 17 and 15 kg·ha–1, respectively, were applied each season. Additional N and K were applied twice weekly through the microirrigation system at 1.12 and 0.92 kg·ha–1·day–1, respectively. Total marketable fruit yield and marketable fruit per plant were not affected by preplant fertilizer rate. The percentage of marketable fruit increased with increased preplant fertilizer to the 51N–45K (three times basic rate) kg·ha–1 rate the first season. Average fruit weight increased the first season but decreased the second season with increased preplant fertilizer. Plants were larger the first season in treatments receiving preplant fertilizer.

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K.G. Childs, T.A. Nell, J.E. Barrett, and D.G. Clark

Experiments were conducted to evaluate the development of stored unrooted Pelargonium × hortorum `Designer Bright Scarlet' cuttings. Treatments included storage temperature and duration and pre-storage fungicide application. Cuttings were harvested from stock plants treated with water or fungicide (Iprodione), and were stored at 60°F and 75°F for 2, 4, and 6 days. Leaf yellowing data (visual quality rating, chlorophyll fluorescence, and total chlorophyll content) were measured at the start of propagation and 7 days later. At both dates, cuttings stored but not treated with fungicide displayed more leaf yellowing after storage at 75°F for 4 and 6 days or at 60°F for 6 days compared to fungicide-treated cuttings and non-stored controls. Cutting quality was not affected by 2 days of storage, regardless of storage temperature or fungicide treatment. Fungicide-treated cuttings had less leaf yellowing after storage for 6 days at 60°F or 75°F compared to untreated cuttings, but they had more leaf yellowing than no storage controls after 7 days of propagation. Root number and root length of each cutting was measured at 14 days after start of propagation. Cuttings treated with fungicide displayed better adventitious root formation after all 4- and 6-day storage treatments compared to cuttings stored but not treated with fungicide.

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J.B. Million, J.E. Barrett, T.A. Nell, and D.G. Clark

Three experiments were conducted to evaluate media component effects on paclobutrazol activity. In Expts. 1 and 2, a broccoli (Brassica oleracea var. botrytis L.) seedling bioassay was used to compare the activity of paclobutrazol at six concentrations (0-0.32 mg·L-1). Results from Expt. 1 indicated that an average of 4-, 5-, and 10-fold higher concentrations were required in old composted pine bark, fresh pine bark, and composted pine bark samples, respectively, to achieve the same activity observed in sphagnum peatmoss (peat) samples. Activity in coir was similar to that in peat while activity in vermiculite and perlite was greater than that in peat. Activity in a fibrous peat sample was greater than in two less-fibrous peat samples. Results from Expt. 2 indicated that paclobutrazol activity was reduced more in the fine (<2 mm) fraction of fresh and composted bark samples than in medium (2-4 mm) or coarse (>4 mm) fractions. In Expt. 3, petunia {Petunia hybrida Vilm. `Madness Red') was grown in a mixture of either 60% composted pine bark: 0% peat or 0% composted bark: 60% peat. The paclobutrazol concentration required to achieve the same size control was 14 times higher in the former mixture than in the latter. Thus, media components differ greatly in their influence on paclobutrazol activity and the bioassay procedure may serve as a useful tool for predicting media-paclobutrazol interactions. Chemical name used: (±)-(R*,R*)-β-[(4-chlorophenyl)methyl]-α-(l,l-dimethyl)-lH-l,2,4-triazole-l-ethanol (paclobutrazol).

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J.E. Barrett, R.K. Schoellhorn, C.A. Bartuska, D.G. Clark, and T.A. Nell

Uniconazole was applied as a spray to the surface of container media prior to planting bedding plant plugs. This medium spray was compared to a standard whole-plant spray applied 2 weeks after planting. For petunia (Petunia ×hybrida Vilm.) and coleus (Solenostemon scutellarioides L.) the efficacy of the medium spray was similar to the whole-plant spray. However, for impatiens (Impatiens wallerana Hook. f.) and vinca [Catharanthus roseus (L.) G. Don.] the medium spray had greater efficacy than the whole-plant spray. Increased concentrations of uniconazole in the medium spray decreased plant height; however, the effect of higher concentrations was greater in a medium with out pine bark compared to a medium with pine bark as a component. In the above experiments, uniconazole was applied in a volume of 200 mL·m-2. In a test where spray volume varied, there was a negative linear relationship between plant height and spray volume. Chemical name used: (E)-(+)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ane-3-ol (uniconazole).

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J.B. Million, J.E. Barrett, T.A. Nell, and D.G. Clark

Contamination of recirculated subirrigation water with growth retardants poses a potential problem for growers. Eight concentrations of ancymidol or paclobutrazol ranging from 0 to 100 μg·L-1 (0 to 1000 μg·L-1 for petunia) were supplied constantly in subirrigation water to potted plants to identify critical levels at which plant growth is affected. Concentrations of ancymidol resulting in 20% reduction in plant size relative to untreated controls were 3, 10, 98, 80, and 58 μg·L-1 for Begonia ×semperflorens-cultorum Hort. `Gin', chrysanthemum (Dendranthema ×grandiflora Kitam.) `Nob Hill', Impatiens walleriana Hook f. `Super Elfin Coral', Petunia ×hybrida Hort. Vilm.-Andr. `Madness Pink', and Salvia splendens Sell ex Roem. & Schult. `Red Hot Sally', respectively. Respective values for paclobutrazol were 5, 24, 17, 390, and >100 μg·L-1. The results provide useful information for managing potential growth retardant contamination problems or for applying growth retardants in subirrigation water. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); (±)-(R*,R*)-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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C. D. Stanley, G. A. Clark, E. E. Albregts, and F. S Zazueta

Sixteen field-located drainage lysimeters (each 60 cm wide, 2.44 m long, 60 cm deep) designed specifically for determination of water requirements for fruiting strawberry production (season - Oct to April) were installed in 1986. Each lysimeter was equipped with individual micro-irrigation and drainage collection systems automated for minimal management input. Initially, computer control (using a low-cost microcomputer) was used to continuously check switching-tensiometers located in each lysimeter and apply irrigation water as needed, A drainage suction (-10 MPa) was applied continuously to simulate field drainage conditions. Manually-installed lysimeter covers were used to protect the plots from interference from rainfall when needed, Initial irrigation application treatments were set at four levels of soil moisture tension controlled by tensiometers and were measured using flow meters for each lysimeter. This paper will discuss problems that were experienced with the initial setup (difficulty in measuring actual application amounts, tensiometer and computer control, elimination of rainfall interference, uniformity of irrigation application, and salinity in the rooting zone) and the modifications (pressurized reservoir tanks, construction of motorized rain-out shelter, micro-irrigation emitters used, and fertilization program) which have been made to overcome them,