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Michael D. Dukes, Lincoln Zotarelli, and Kelly T. Morgan

Major horticultural crops in Florida are vegetables, small fruit, melons, and tree fruit crops. Approximately half of the agricultural area and nearly all of the horticultural crop land is irrigated. Irrigation systems include low-volume microirrigation, sprinkler systems, and subsurface irrigation. The present review was divided into two papers, in which the first part focuses on vegetable crop irrigation and the second part focuses on fruit tree crop irrigation. This first part also provides an overview of irrigation methods used in Florida. Factors affecting irrigation efficiency and uniformity such as design and maintenance are discussed. A wide range of soil moisture sensors (e.g., tensiometers, granular matrix, and capacitance) are currently being used in the state for soil moisture monitoring. Current examples of scheduling tools and automated control systems being used on selected crops in Florida are provided. Research data on the effect of irrigation scheduling and fertigation on nutrient movement, particularly nitrate, are reviewed. Concluding this review is a discussion of potential for adoption of irrigation scheduling and control systems for vegetable crops by Florida growers and future research priorities.

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Kelly T. Morgan, Lincoln Zotarelli, and Michael D. Dukes

Florida is the most important center of processed citrus (Citrus spp.) production in the United States, and all of the crop is irrigated. Irrigation systems include low-volume microirrigation, sprinkler systems, and subsurface irrigation. This review details the relative irrigation efficiencies and factors affecting irrigation uniformity such as design and maintenance. A wide range of soil moisture sensors (e.g., tensiometers, granular matrix, and capacitance) are currently being used for citrus in the state. The use of these sensors and crop evapotranspiration estimation using weather information from the Florida Automated Weather Network in irrigation scheduling are discussed. Current examples of scheduling tools and automated control systems being used on selected fruit crops in Florida are provided. Research data on the effect of irrigation scheduling, soluble fertilizer injection, and soil nutrient movement, particularly nitrate and the use of reclaimed water in Florida, are also reviewed. Concluding this review is a discussion of the potential for adoption of irrigation scheduling and control systems for citrus by Florida growers and future research priorities.

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Johannes Scholberg, Kelly Morgan, Lincoln Zotarelli, Eric Simonne, and Michael Dukes

Most strategies used to determine crop N fertilizer recommendations do not address potential environmental issues associated with agricul-tural production. Thus, a more holistic approach is required to reduce N loading associated with vegetable crops production on soils that are prone to N leaching. By linking fertilizer N uptake efficiency (FUE) with irrigation management, root interception capacity, and N uptake dynamics, we aim to improve FUE. Nitrogen uptake for peppers, tomato, potato, and sweet corn followed a logistic N accumulation patterns. Up to 80-85% of N uptake occurred between 4 to 7 weeks (sweet corn) vs. 6 to 12 weeks (other crops), while N uptake during initial growth and crop maturation was relatively low. Maximum daily N accumulation rates occurred at 5 weeks (sweet corn) vs. 8-10 weeks (other crops) and maximum daily N uptake rates were 4-8 kg N/ha. Overall FUE for most vegetables may range between 23% and 71%, depending on production practices, soil type, and environmental conditions. Maximum root interception capacity was typically attained 3 to 5 weeks prior to crop maturity. It is concluded that, during initial growth, root interception may the most limiting factor for efficient N use. Although recent uptake studies have shown that FUE may be highest toward the end of the growing season, this may not coincide with the greatest crop demand for N, which occurs during the onset of the linear growth phase. As a result, yield responses to N applied later in the season may be limited. Integration of these results into best management practices and expert systems for vegetable production can minimize the externalities associated with commercial vegetable production on vulnerable soils in the southeastern United States.

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Thomas R. Sinclair, Andrew Schreffler, Benjamin Wherley, and Michael D. Dukes

Although root development is critical in the establishment of turfgrass sod, there appears to be no information on the response of root development during sod establishment to the frequency and amount of irrigation. Two alternate hypotheses for the root development response are that 1) frequent and high amounts of irrigation are needed to support sod growth and root development; and 2) deficit irrigation encourages more rapid and deeper rooting. The objective of this study was to observe root development of four warm-season turfgrasses subjected to various frequencies and amounts of irrigation. Root extension of the grasses was observed directly in soil contained in 90-cm tall, clear acrylic columns. No difference in root development was observed for any of the grasses among irrigation frequency treatments of daily, twice weekly, and once weekly. There were differences in response to the amount of irrigation. Zoysiagrass root development was maximal at the full amount of irrigation (35 mm per week). On the other hand, St. Augustinegrass, bermudagrass, and bahiagrass required deficit irrigation of only 13 mm water per week to achieve full root development. The results of this study showed that each of the two hypotheses were appropriate depending on the specific species.

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Lincoln Zotarelli, Johannes Scholberg, Michael Dukes, Hannah Snyder, Eric Simonne, and Michael Munoz-Carpena

On sandy soils, potential N contamination of groundwater resources associated with intensively managed vegetables may hamper the sustainability of these systems. The objective of this study was to evaluate the interaction between irrigation system design/scheduling and N fertilization rates on zucchini production and potential N leaching. Zucchini was planted during Fall 2005 using three N fertilizer rates (73, 145, 217 kg/ha) and four different irrigation approaches. Irrigation scheduling included surface-applied drip irrigation and fertigation: SUR1 (141 mm applied) and SUR2 (266 mm) using irrigation control system (QIC) that allowed time-based irrigation (up to five events per day) and a threshold setting of 13% and 15% volumetric water content (VWC), respectively; Subsurface drip irrigation (SDI) using a QIC setting of 10% VWC (116 mm) combined with surface applied fertigation; and a control treatment with irrigation applied once daily (424 mm). Leacheate volumes were measured by drainage lysimeters. Nitrate leaching increased with irrigation rate and N rate and measured values ranged from 4 to 42 kg N/ha. Use of SDI greatly reduced nitrate leaching compared to other treatments. SDI and SUR1 treatments had no effect on yields (29 Mg/ha). However, SDI had a 15% and 479% higher water use efficiency (WUE) compared to SUR1 and the fixed irrigation duration treatment. Application of N in excess of intermediate N-rate (standard recommendation) did not increase yield but yield was reduced at the lowest N-rate. It is concluded that combining sensor-based SDI with surface applied fertigation resulted similar or higher yields while it reduced both water use and potential N leaching because of improved nutrient retention in the active root zone.

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Aparna Gazula, Eric Simonne, Michael Dukes, George Hochmuth, Bob Hochmuth, and David Studstill

Collecting leachate from lysimeters installed in the field below vegetable fields may be used to quantify the amount of nitrogen released into the environment. Because limited information exists on the optimal design type and on the effect of design components on lysimeter performance, the objective of this study were to identify existing designs and their limits, assess cost of design, and test selected designs. Ideally, lysimeters should be wide enough to collect all the water draining, long enough to reflect the plant-to-plant variability, durable enough to resist degradation, deep enough to allow for cultural practices and prevent root intrusion, have a simple design, be made of widely available materials, and be cost-effective. Also, lysimeters should not restrict gravity flow thereby resulting in a perched water table. Previous study done with a group of free-drainage lysimeters (1-m-long, 45-cm-wide, installed 45-cm-deep) under a tomato-pumpkin-rye cropping sequence resulted in variable frequency of collection and volume of leachate collected (CV of load = 170%). Improving existing design may be done by increasing the length of collection, lining the lysimeter with gravel, limiting the depth of installation, and/or breaking water tension with a fiberglass wick. Individual lysimeter cost was estimated between $56 to $84 and required 9 to 14 manhours. for construction and installation. Costs on labor may be reduced when large numbers of lysimeters are built. Labor needed for sampling 24 lysimeters was 8 man-hr/sampling date. Because load may occur after a crop, lysimeter monitoring and sampling should be done year round.

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Maria C. Morera, Paul F. Monaghan, Michael D. Dukes, Ondine Wells, and Stacia L. Davis

Smart irrigation controllers are capable of substantially decreasing landscape water applications under residential high water-use conditions in Florida. Their implementation has been incentivized by governmental agencies and water utilities in an effort to reduce public-supply water demand and conserve water resources. However, the bulk of the research on smart controllers for urban landscapes has focused on performance dimensions. To successfully promote them, feedback from end-users is critical. This paper provides an evaluation of homeowner response to evapotranspiration (ET)-based and soil moisture sensor (SMS)-based smart controllers installed as part of a pilot project conducted in Orange County, FL. The objectives of the study were to collect demographic information, assess conservation attitudes and irrigation system knowledge, and gather feedback on the use of smart controllers from the pilot project’s residential cooperators. Data were collected through an online survey and analyzed using relative frequency distributions, text analysis, independent means t tests, and logistic regression. Results indicated that a majority of survey participants were satisfied with their controllers and planned to continue using them. Both ET and SMS controllers were consistently praised for saving money and irrigating efficiently. However, the likelihood that participants would continue using their controllers after the completion of the project was only significantly predicted by their levels of technical knowledge regarding the workings of the devices and whether they had experienced any challenges operating them. Efforts to promote both initial and long-term adoption may be most effective by emphasizing the economic benefits of investing in smart irrigation controllers and by disseminating best management practices that facilitate their understanding and successful operation.

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Rafael Muñoz-Carpena, Yuncong C. Li, Waldemar Klassen, and Michael D. Dukes

A low-volume/high frequency (LVHF) soil moisture-based drip irrigation system was tested on a shallow sandy soil at a commercial tomato (Lycopersicon esculentum) farm in southern Florida. Six LVHF irrigation treatments were compared with the standard commercial practice on the farm (control), where a portable pump was used for manual drip irrigation twice each week. In the six LVHF treatments the system was continuously pressurized by means of an electrical pump and a pressure tank, and controlled by an irrigation timer set to irrigate a maximum of five times per day with the irrigation time (i.e., volume) set according to historical evapotranspiration (ET) demands in the area. Two treatments were based on timer schedules, one to supply 100% of the maximum recommended crop water needs in the area based on historical ET (ET-100%), and the other to supply 150% of those needs (ET-150%). The other four treatments were created by interfacing two types of soil moisture sensors (switching tensiometers and granular matrix sensors with control modules) set at two moisture points (wet = 10 kPa, optimal = 15 kPa) in a closed control loop with the irrigation timer programmed at the ET-100% schedule. Results showed that the six LVHF treatments reduced water use while not significantly affecting tomato yields. Switching tensiometers at the 15 kPa set point performed the best (up to 73% reduction in water use when compared to the control, 50% with respect to ET-100%). The results show that water use below historical ET levels can be obtained without sacrificing yield by keeping the root zone moisture at controlled levels with the soil-moisture based system. Routine maintenance was critical for reliable operation of the switching tensiometers. Granular matrix sensor based irrigation behaved erratically, and did not improve water savings compared to ET-100%, indicating that this system was not effective under the conditions of the area due to the sensor's slow response to frequent wetting-rewetting cycles and characteristics of the interface.

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Lincoln Zotarelli, Johannes Scholberg, Michael Dukes, Hannah Snyder, Rafael Munoz-Carpena, and Eric Simonne

Several practices have been adopted to minimize water use and potential N leaching of vegetable production systems, including use of drip irrigation, plastic mulch, and fertigation. However, these practices may not be adequate on sandy soils with poor water and nutrient retention capacities. The objectives of this study were to evaluate the interactive effects of irrigation practices and fertilizer rates on yield, fertilizer requirements, and N-leaching of pepper and tomato production systems. Bell pepper and tomato were planted on plastic mulched to evaluate the effects of three nitrogen (N) fertilizer rates (154, 192, 288 kg·ha -1 N for pepper vs. 166, 208, and 312 kg·ha-1 N for tomato) and three irrigation scheduling methods were evaluated. Depending on sensor readings, soil moisture sensor (SMS) irrigation treatments allowed up to five watering events per day where as for the fixed duration treatment irrigation was applied once a day. For tomato, the effect of subsurface drip irrigation (SDI) was also evaluated. Compared to TIME, use of SMS control system reduced water use by 29& to 44% and 37% to 66% for tomato and pepper, respectively. Tomato yield was significantly higher on SMS and SDI treatments compared to TIME treatments. For pepper yield and biomass accumulation were not affected by irrigation treatments. The average yields were 24.6 and 27.8 Mg·ha-1 of fresh marketable fruits for pepper and tomato, respectively. Nitrogen rate did not affect yield and optimal yield N rate did not affect yield for either crop. On average, SMS treatments increased irrigation water use efficiency 2–3 times compared to TIME treatments for both tomato and pepper.

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Sarah E. Cathey, Jason K. Kruse, Thomas R. Sinclair, and Michael D. Dukes

Water management and turfgrass breeding efforts focused on water conservation can benefit from a better understanding of drought stress physiology because it relates to visual quality. In a repeated study under controlled conditions, ‘Argentine’ bahiagrass (Paspalum notatum Flugge), ‘Floratam’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and ‘Empire’ zoysiagrass (Zoysia japonica Steud.) were subjected to drought stress as defined by the normalized transpiration ratio (NTR) of drying to well-watered plants. Differences in total water extracted from the soil as the soil dried to stomatal closure were not different among grasses; however, zoysiagrass had the slowest water use rate and less firing under increasing drought stress than the other grasses. Optical sensing of the normalized difference vegetation index from the turf canopies was not an effective predictor of drought stress for either study. In both studies, severe wilting and some firing occurred in bahiagrass and st. augustinegrass when NTR was 0.3. Zoysiagrass was not severely wilted until 0.1 NTR and exhibited little firing even after drying had continued for an additional 7 days past 0.1 NTR. After 7 days at well-watered status after drought stress to a severity of 0.1 NTR, all grasses were able to recover to an acceptable visual quality rating. This recovery from severe wilt and some canopy firing (except for zoysiagrass), indicating that a return to well-watered soil after severe stress, can result in acceptable turf recovery.