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G.A. Clark

Proper management of vegetable drip-irrigation systems requires knowledge of soil hydraulic characteristics, plant-growth and water-use characteristics, and evaporative demand. The resultant schedule must integrate these properties and conform to existing irrigation system and cultural constraints. Irrigation management must be coupled with the fertilizer management program to avoid excessive water applications that leach plant nutrients. Because drip irrigation applies water to discrete locations along the plant row, limited irrigated areas can result, and this is an important consideration for irrigation system design, cultural practices and management, and irrigation system operation and management.

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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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Gary A. Clark and Allen G. Smajstrla

The injection of chemicals into irrigation systems is discussed in terms of injection systems, concentration injections, bulk injections, quantity of chemicals to be injected, injection system calibration, and injection periods. Sufficient clean-water flush time should be scheduled to purge irrigation lines of injected chemicals unless it is desired to leave that particular chemical in the irrigation system for maintenance purposes. Chemical injection rates vary with desired chemical concentration in the irrigation water, concentration of the stock solution, volume of chemical to be injected, and duration of each injection. All injection systems should be calibrated and maintained in proper working order. This information is presented to assist irrigation system designers and operators with chemigation system design, scheduling, and management.

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Gary A. Clark and Allen G. Smajstrla

Proper design and installation are essential to provide a drip irrigation system that can be managed with minimal inputs and maximum profit. Because drip irrigation can apply precise amounts of water and chemicals, constraints associated with the plants, soil, water supply, and management must be considered in the design, installation, and management processes.

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

Combinations ofvarious vegetable crop species grown in multiple-cropping sequences using microirrigation on a sandy soil were evaluated for production potential and changes in normal cultural management An initial fall-season fresh-market tomato crop was followed immediately by a winter-season crucifer crop (cauliflower, broccoli, or cabbage), which was followed by a spring-season cucurbit crop (cucumber, zucchini squash, or muskmelon). Studies were conducted over a 3-year period in southwestem Florida. Results showed that when cropping sequences were compared on a basis of a derived relative value index (RVI), the sequence of tomato-cauliflower-zucchini squash significantly outperformed other sequences. Several management concerns particular to the production system (crop residue removal and interference, plastic mulch deterioration and damage, and weed control) were identified and discussed. The potential savings when cropping sequences are compared to individual crop production resulted in net savings (dollar savings less additional production costs) that ranged from $565 to $1212/acre ($1396 to $2993/ha) and $614 to $1316/acre ($1516 to $3251/ha) for the 1986-87 and 1988-89 seasons, respectively.

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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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C.E. Wieland, J.E. Barrett, C.A. Bartuska, D.G. Clark, and T.A. Nell

Salvia (Salvia splendens F.), vinca (Catharanthus roseus L.), and pansy (Viola × wittrockiana Gams.) were examined to determine efficacy of growth retardants for inhibiting stem elongation of seedlings in the plug stage and after transplanting to 10-cm pots. Studies on salvia showed plugs sprayed with single applications of ancymidol at 10 or 20 ppm, paclobutrazol at 30 or 60 ppm, or daminozide/chlormequat tank mix at 2500/1500 ppm inhibited plug elongation by 17% to 22%. Pansy plugs were sprayed either once or twice with ancymidol at 5, 10, or 15 ppm. Number of applications was statistically significant with two applications reducing elongation by an average of 35%, whereas a single application resulted in a 23% average reduction. Ancymidol concentration was significant in reducing stem elongation with increasing rates in pansy; however, the concentration and application time interaction was not significant. In both pansy and salvia, plant size at flowering was similar to controls after transplanting. Vinca plugs were sprayed with ancymidol at 5, 10, or 15 ppm either the 3rd week, 4th week, or both weeks after sowing. As ancymidol concentrations increased, plug height decreased, and the concentration effect was greater week 3 than at week 4. Two applications of ancymidol was most effective in retarding stem elongation (36%) followed by one spray the 3rd week (29%) and one spray during week 4 (20%).