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  • Author or Editor: A.G. Smajstrla x
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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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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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Tomatoes (Lycopersicon esculentum Mill.) were grown on an Arredondo fine sandy soil to evaluate the effects of water quantity scheduled by pan evaporation using drip irrigation and polyethylene mulch in a three year study. Water was applied at 0, 0.25, 0.50, 0.75, and 1.0 times pan evaporation in one application per day. The response to irrigation varied with rainfall during the three seasons. In an extremely dry season, fruit yields were doubled by irrigation. Total fruit yields were highest with irrigation quantities of 0.75 and 1.0 times pan and significantly lower with 0.25 and 0.50 times pan water quantity. In an extremely wet season, fruit yields were not influenced by water quantities from 0 to 1.0 times pan. In a third season that was wet from the middle to the end of the season, irrigation more than doubled the marketable yield. However, yield increased only from 65.9 Mt·ha-1 with 0.25 times pan to 74.1 Mt·ha-1 with 0.75 times pan. Tomato leaf N concentrations were reduced slightly with each increase in water quantity applied even though N was applied with drip irrigation.

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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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Two-year-old, container-grown rabbiteye (Vaccinium ashei Reade) and high-bush (Vaccinium corymbosum L.) blueberry plants were used in a 3-year study of water requirement for blueberry production in Florida. The rabbiteye cultivars Powderblue and Premier and the highbush cultivar Sharpblue were grown under three irrigation regimes. Irrigation events were triggered when soil water tensions in the upper 15 cm of the containers reached either 10, 15, or 20 kPa. Neither yield nor vegetative growth of rabbiteye cultivars differed among treatments. During the third year, the growth increase in highbush blueberry was significantly greater in the 10-kPa than in the 15- and 20-kPa treatments. The highest water treatment (10 kPa) resulted in a significant yield increase for the highbush cultivar.

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Tomato (Lycopersicon esculentum Mill.) was grown with drip irrigation on an Arredondo fine sand and on an Orangeburg fine sandy loam to evaluate the effect of N and K time of application on petiole sap, leaf-N and -K concentrations, fruit yield, and to determine N and K sufficiency ranges in leaf tissue. On the sandy soil, N—K at 196-112 kg·ha-1 were applied 0%, 40%, or 100% preplant with the remainder applied in 6 or 12 equal or in variable applications in 12 weeks. With the variable application rate, most nutrients were applied between weeks 5 and 10 after transplanting. On the sandy loam soil that tested high in K, only N (196 kg·ha-1) was applied as above. Petiole sap K concentration declined during the season, but was not greatly affected by treatment. Petiole NO3-N concentrations decreased during the season from 1100 to 200 mg·L-1, and the decrease was greater with preplant N treatments. On the sandy soil, marketable fruit yields were lowest with 100% preplant, intermediate with 100% drip applied (no preplant N), and highest with 40% preplant and 60% drip applied. With 100% drip applied, yields were higher with 12 even applications than with either six even weekly applications or with 12 variable N and K applications. With 40% preplant, timing of application had little effect on yield. On the sandy loam soil in 1993, yields were highest with 100% preplant, intermediate with 40% preplant and 60% drip applied, and lowest with all N drip applied. In 1994 when excessive rains occurred, yields were similar with all preplant and with split N applications. Petiole N concentration was correlated with tomato yield, especially at 10 weeks after transplanting. The best correlation between sap-N and total yields occurred between 4 and 6 weeks at Gainesville and between 4 and 10 weeks at Quincy.

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