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Laura Avila, Johannes Scholberg, Lincoln Zotarelli and Robert McSorely

Poor water- and nutrient-holding capacity of sandy soils, combined with intense leaching rainfall events, may result in excessive N-fertilizers losses from vegetable production systems. Three cover cropping (CC) systems were used to assess supplemental N-fertilizer requirements for optimal yields of selected vegetable crops. Fertilizer N-rates were 0, 67, 133, 200, and 267; 0, 131, and 196; and 0, 84, 126,168, and 210 kg N/h for sweet corn (Zea mays var. rugosa), broccoli (Brassica oleracea), and watermelon (Citrullus lanatus), respectively. Crop rotations consisted of sunn hemp (Crotalaria juncea) in Fall 2003 followed by hairy vetch (Vicia villosa), and rye (Secale cereale) intercrop or a fallow. During Spring 2004, all plots were planted with sweet corn, followed by either cowpea (Vigna unguiculata) or pearl millet (Pennisetum glaucum), which preceded a winter broccoli crop. Hairy vetch and rye mix benefited from residual N from a previous SH crop. This cropping system provided a 5.4 Mg/ha yield increment for sweet corn receiving 67 kg N/ha compared to the conventional system. For the 133 N-rate, CC-based systems produced similar yields compared to conventional systems amended with 200 kg N/ha. Pearl millet accumulated 8.8 Mg/ha—but only 69 kg N/ha—and potential yields with this system were 16% lower compared to cowpea system. For a subsequent watermelon crop, trends were reversed, possibly due to a delay in mineralization for pearl millet. Because of its persistent growth after mowing, hairy vetch hampered initial growth and shading also delayed fruit development. Although CC may accumulate up to 131 kg N/ha actual N benefits, N-fertilizer benefits were only 67 kg N/ha, which may be related to a lack of synchronization between N release and actual crop demand.

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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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Mildred N. Makani, Steven A. Sargent, Lincoln Zotarelli, Donald J. Huber and Charles A. Sims

Early-maturing potato cultivars (Solanum tuberosum L.) grown in many subtropical and tropical regions are typically packed and shipped without curing. The objective of this study was to evaluate two early-maturing potato cultivars (‘Fabula’ and ‘Red LaSoda’) grown under four nitrogen fertilizer (NF) rates and harvested at three intervals after vine kill for effects on tuber physical and compositional quality at harvest and during storage. NF was applied through fertigation (0, 112, 224, or 336 kg·ha−1) and compared with granular NF application (224 kg·ha−1). The tubers were harvested weekly after vine kill (H1, H2, and H3) then evaluated for quality at 7 and 14 days during storage at 10 °C/80% to 85% relative humidity (RH). ‘Fabula’ tubers from H1 had the highest cumulative weight loss (3.6%) after 14 days of storage (season 1), while those from both H1 and H2 were highest (4.4%) in season 2, regardless of NF application method or rate. Tuber firmness increased by 1.5 newtons (N) for tubers from H1 after 7 days storage, and again by 0.76 N after 14 days for tubers from H2 and H3. Periderm dry matter content (DMC) for H1 tubers increased to 13.9% after 7 days, regardless of fertilizer treatment, in contrast to those from H2 or H3 where DMC remained constant throughout storage (10.6% and 11.4%, respectively). For ‘Red LaSoda’, cumulative weight loss in season 1 for H1 tubers was 2.2% after 14 days storage, whereas that for H2 and H3 tubers averaged 0.7%; this trend was similar for season 2. Periderm DMC significantly increased with increased storage time; that for H2 tubers was highest (19.6%) after 14 days. In both cultivars, tuber ascorbic acid content (AAC), soluble solids content (SSC), and total titratable acidity (TTA) remained constant throughout the 14-day storage period. Periderm maturity of ‘Fabula’ and ‘Red LaSoda’ potatoes had a greater effect on tuber physical and compositional quality during storage than the fertilizer rates or application methods. Fertigation at NF rates of 112, 224 or 336 kg·ha−1 was comparable with conventional granular NF application for growing high-quality tubers with acceptable postharvest life. Growing tubers at 112 kg·ha−1 nitrogen via fertigation has the potential to reduce both irrigation water usage and fertilizer runoff during the production cycle.

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Fernanda Souza Krupek, Christian T. Christensen, Charles E. Barrett and Lincoln Zotarelli

The cost of seed accounts for nearly 10% of the estimated production cost of chipping potato (Solanum tuberosum) production in Florida. Optimizing seed piece spacing can reduce costs without affecting potato yield. This study evaluated the effects of seed piece spacing on yield, quality, and economic revenue of chipping potato production in north Florida. A field experiment was conduct during the spring of 2013, 2014, and 2016 in Hastings, FL, with a split-plot randomized complete block design. In-row seed piece spacings of 10, 15, 20 (industry standard), 25, and 30 cm were assigned as the main plot and S. tuberosum potato cultivars (Atlantic, Harley Blackwell, and Elkton) as the subplots. Marketable tuber yield ranged between 10.8 and 15.2 Mg·ha−1 in 2013, 10.1 and 12.8 Mg·ha−1 in 2014, and 9.9 and 19.7 Mg·ha−1 in 2016. Overall lower yields in 2013 were due to three freeze events early in the season. Widening seed piece spacing resulted in a linear decrease in total and marketable yield in 2013 and 2014. Conversely, seed piece spacings of 10 and 15 cm showed lower marketable yields in 2016. There was no interaction between in-row spacing and cultivar in any year tested. Cultivars performed variably across years for total and marketable yield and specific gravity. Tuber specific gravity was unaffected by seed piece spacing, except in 2013, when 25 and 30 cm resulted in slightly higher values. There was no significant difference in total and marketable yield between the industry standard seed piece spacing 20 and 25 cm in any year. In-row spacing of 25 cm in 2013 and 30 cm seed piece spacing in 2014 and 2016 provided the greatest economic return. Net revenue can be increased by adjusting the in-row seed piece spacing from the commercial standard of 20 to 25 cm, which reduces production cost without negatively impacting yields.

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Emmanuel A. Torres-Quezada, Lincoln Zotarelli, Vance M. Whitaker, Bielinski M. Santos and Ixchel Hernandez-Ochoa

The standard strawberry (Fragaria ×ananassa) production system in Florida uses bare-root transplants with three to five leaves; however, commercial transplants are typically variable in size. The objective of this experiment was to study the effects of transplant crown diameter on the subsequent performance of three short-day strawberry cultivars under central Florida conditions. Trials were carried out during the 2012–13 and 2013–14 growing seasons with six treatments resulting from the combination of three cultivars and two crown diameter categories. Transplants of ‘Florida Radiance’, ‘Strawberry Festival’, and WinterStar™ were sorted into two initial crown diameter size ranges: <10 mm and >10 mm. Treatments were established in a split-plot design with cultivars as the main plot and four replications. Dry plant biomass was collected at 6 weeks after transplant (WAT). Canopy diameter and crown diameter were measured at 6 and 18 WAT and fruit harvest started at 8 WAT. There were no interactions between cultivar and initial crown diameter for any of the measured variables. For early yield, larger crowns led to 46% (3.5 Mg·ha−1) and 38% (3.9 Mg·ha−1) higher early yield than smaller crowns in 2012–13 and 2013–14, respectively. Crown diameters >10 mm also resulted in 18% (23.5 Mg·ha−1) and 27% (17.4 Mg·ha−1) higher total yields in 2012–13 and 2013–14, respectively.

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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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Charles E. Barrett, Lincoln Zotarelli, Lucas G. Paranhos, Peter Dittmar, Clyde W. Fraisse and John VanSickle

Weather has a major influence on cabbage (Brassica oleracea var. capitata L.) production. Variation in yield between years and cropping seasons is common in North America. Cabbage in Florida has historically been cultivated on bare ground with seepage irrigation. The objectives of this study were to compare yield and profit of a bare ground cabbage production system used in Florida with an alternative plasticulture system. Data from various cabbage trials were combined by production system and used to create regression equations that predicted yield based on air temperature and solar radiation that were significantly correlated with yield. The regression equations were then simulated with correlated stochastic air temperature and solar radiation to estimate the yield distributions for both systems. Cabbage price ($/Mg fresh) was stochastically simulated (correlated to yield) to be used in the profit model. The profit model was created by using the product of yield and the price per unit yield minus fixed and variable costs associated with production and marketing. Simulated profit for bare ground and plasticulture was used to estimate their respective distributions to provide a tool for making better management decisions in the presence of risky weather conditions. The plasticulture system was estimated to have a 36% higher cost but a 57% higher profit than the bare ground system. This is, in large part, because the simulated mean yield for the bare ground system was 29.7 Mg·ha−1 compared with 54.4 Mg·ha−1 for plasticulture. These findings confirmed that plasticulture is an economically viable best management practice for cabbage production in Northeast Florida.

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Lucas G. Paranhos, Charles E. Barrett, Lincoln Zotarelli, Tatiana Borisova, Rebecca Darnell and Kati Migliaccio

Seepage is characterized as an inefficient irrigation method with regard to water and nutrient use. There is a need for an economically viable irrigation alternative to seepage, which increases crop productivity and profitability in Florida. The use of plastic mulch and drip irrigation for cabbage (Brassica oleracea var. capitata) production increases plant population per area and reduces the irrigation water requirement. However, plasticulture has a high capital investment and operating cost. The objectives of this study were to compare the profitability of plasticulture cabbage production and traditional seepage bare ground irrigation systems for Florida cabbage production, and to determine the breakeven point for cabbage grown under plasticulture given a range of market prices. The preharvest cost per acre for the plasticulture system was significantly higher than the cost for the seepage system ($4726 and $3035 per acre, respectively). However, for all planting dates considered in this study, the plasticulture system resulted in a significant increase in marketable yields when compared with the seepage system. The resulting increase in potential revenue offset the increase in preharvest costs and assured a positive net return on investment over the whole range market prices. It was also observed that low air temperatures combined with reduced solar radiation can prevent optimum plant development for cabbage transplanted between November and mid-December. Therefore, the return on investment may be reduced during less favorable climatic conditions for cabbage growth, making the plasticulture system less economically desirable for certain planting dates.