Current Knowledge, Gaps, and Future Needs for Keeping Water and Nutrients in the Root Zone of Vegetables Grown in Florida

in HortTechnology
Authors:
Eric Simonne1State Extension Specialists/Researchers, University of Florida/IFAS Horticultural Sciences Department, 1241 Fifield Hall, P.O. Box 110690, Gainesville, FL 32611-0690

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Chad Hutchinson1State Extension Specialists/Researchers, University of Florida/IFAS Horticultural Sciences Department, 1241 Fifield Hall, P.O. Box 110690, Gainesville, FL 32611-0690

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Jim DeValerio2County Extension Agent, Bradford County, 2266 N. Temple Avenue, Starke, FL 32091-1612

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Robert Hochmuth3Multi-county Extension Agent, North Florida Research and Education Center - Suwannee Valley, 7580 CR 136, Live Oak, FL 32060

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Danielle Treadwell1State Extension Specialists/Researchers, University of Florida/IFAS Horticultural Sciences Department, 1241 Fifield Hall, P.O. Box 110690, Gainesville, FL 32611-0690

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Allan Wright4State Extension Specialist/Researcher, UF/IFAS Soil and Water Science Department, Everglades Research and Education Center, 3200 E Palm Beach Rd., Belle Glade, FL 33430

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Bielinski Santos5State Extension Specialist/Researcher, UF/IFAS Horticultural Sciences Department, UF/IFAS Gulf Coast Research and Education Center, 14625 CR 672, Wimauma, FL 33598

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Alicia Whidden6County Extension Agent, Hillsborough County, 5339 CR 579, Seffner, FL 33584-3334

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Gene McAvoy7Multi-county Extension Agent, South West Florida, 1085 Pratt Blvd., LaBelle, FL 33935

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Xin Zhao1State Extension Specialists/Researchers, University of Florida/IFAS Horticultural Sciences Department, 1241 Fifield Hall, P.O. Box 110690, Gainesville, FL 32611-0690

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Teresa Olczyk8County Extension Agent, Miami-Dade County, 18710 SW 288th St., Homestead, FL 33030

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Aparna Gazula9Former UF/IFAS Horticultural Sciences Department Graduate Research Assistant; Currently County Extension Agent, Alachua County 2800 NE 39th Ave., Gainesville, FL 32609-2658

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Monica Ozores-Hampton10State Extension Specialist/Researcher, Southwest Florida Research and Education Center, N 29th St., Immokalee, FL 34142

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The success of the best management practices (BMPs) program for vegetables in Florida is measured by the level of BMP implementation and the improvement of water quality. Both require keeping water and fertilizer in the root zone of vegetables. The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension Vegetable Group has identified the fundamental principles of 1) basing UF/IFAS production recommendations on the rigors of science and the reality of field production; 2) replacing the out-of-date paradigm “pollute less by reducing nutrient application rates” with “improve water management and adjust fertilizer programs accordingly”; 3) engaging growers, consultants, educators, and regulators in open-channel discussions; and 4) regularly updating current fertilization and irrigation recommendations for vegetables grown in Florida to reflect current varieties used by the industry. The group identified 1) developing ultralow-flow drip irrigation; 2) assisting conversion from seepage to drip irrigation; 3) using recycled water; 4) developing controlled-release fertilizers for vegetables; 5) developing real-time management tools for continuous monitoring of soil water and chemical parameters; 6) developing yield mapping tools for vegetable crops; 7) developing and testing drainage lysimeter designs suitable for in-field load assessment; and 8) using grafting and breeding to develop commercially acceptable varieties with improved nutrient use efficiency by improving morphological, biochemical, and chemical traits as new strategies to keep nutrients in the root zone. These strategies should become funding priorities for state agencies to help the vegetable industry successfully transition into the BMP era.

Abstract

The success of the best management practices (BMPs) program for vegetables in Florida is measured by the level of BMP implementation and the improvement of water quality. Both require keeping water and fertilizer in the root zone of vegetables. The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Extension Vegetable Group has identified the fundamental principles of 1) basing UF/IFAS production recommendations on the rigors of science and the reality of field production; 2) replacing the out-of-date paradigm “pollute less by reducing nutrient application rates” with “improve water management and adjust fertilizer programs accordingly”; 3) engaging growers, consultants, educators, and regulators in open-channel discussions; and 4) regularly updating current fertilization and irrigation recommendations for vegetables grown in Florida to reflect current varieties used by the industry. The group identified 1) developing ultralow-flow drip irrigation; 2) assisting conversion from seepage to drip irrigation; 3) using recycled water; 4) developing controlled-release fertilizers for vegetables; 5) developing real-time management tools for continuous monitoring of soil water and chemical parameters; 6) developing yield mapping tools for vegetable crops; 7) developing and testing drainage lysimeter designs suitable for in-field load assessment; and 8) using grafting and breeding to develop commercially acceptable varieties with improved nutrient use efficiency by improving morphological, biochemical, and chemical traits as new strategies to keep nutrients in the root zone. These strategies should become funding priorities for state agencies to help the vegetable industry successfully transition into the BMP era.

Best management practices (BMPs) are cultural practices that aim at improving the quality of Florida waters while maintaining or improving productivity [Florida Department of Agriculture and Consumer Services (FDACS), 2005]. Because water is the carrier of soluble nutrients and sediments, the overall goal of BMP implementation is to keep water and nutrients in the root zones of vegetables. This report 1) describes the typical nutrient management systems used in Florida for vegetable crop production; 2) compiles known estimates of nutrient load; 3) discusses the feasibility of zero-discharge systems for vegetables; 4) assesses the potential role of breeding and grafting on improving vegetable crop nutrient use efficiency; and 5) develops a vision on what the Florida vegetable industry at large could do to improve water quality. The state agencies involved in BMP in Florida are FDACS, the Florida Department of Environmental Protection, the five water management districts of Florida, and the University of Florida Institute of Food and Agricultural Sciences. These agencies may find these topics useful in planning and coordinating funding allocation, identifying future research needs, and supporting educational programs.

Current nutrient and water management practices used by Florida producers

Vegetables are grown on three main types of soils (sandy, organic, and calcareous soils) using three main types of irrigation methods (overhead, drip, and/or seepage irrigation), two main types of production systems (bare ground or mulched crop), and three seasons (fall, winter, and spring). This diversity creates a wide array of production systems over varying weather conditions, each having its own requirements for water and nutrient management. These systems were recently reviewed in a white paper published by the UF/IFAS Vegetable Fertilizer Task Force (Cantliffe et al., 2006). Production recommendations support the use of on-farm weather data, soil tests, soil moisture-sensing devices (mostly for drip- and overhead-irrigated crops), water table monitoring tools (for seepage-irrigated crops), whole-leaf analysis, and/or petiole sap tests to schedule irrigation and monitor crop nutrition. Success stories on how these tools have helped improve on-farm water and nutrient management have been reported with muskmelon (Cucumis melo) and watermelon (Citrullus lanatus) (Simonne et al., 2005) and strawberry [Fragaria ×ananassa (Hochmuth et al., 2003c)].

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Crop-by-crop fertilizer recommendations for vegetables grown on sandy soils may be found in the Vegetable Production Handbook for Florida (Olson and Simonne, 2007). UF/IFAS fertilizer recommendations include a base fertilizer rate and a supplemental application allowed after a leaching rain (defined as 3 inches of rainfall in 3 d or 4 inches in 7 d), an extended harvest season, and/or when plant nutritional status is diagnosed as “low” based on whole leaf analysis or petiole sap testing. Recommendations also include fertilizer placement (banded, broadcast, or modified broadcast), fertilizer sources when necessary, preplant fertilizer application amounts, and fertigation schedules. These fertilizer recommendations, based on research from the 1980s and 1990s, propose a single nitrogen (N) rate for all irrigation systems, production seasons, and Florida soil types (Olson and Simonne, 2007). Recommendations for phosphorus (P), potassium, calcium, magnesium, and micronutrient applications on sandy soils are based on Mehlich 1 soil test results. Recommendations for vegetable crops grown on muck soils are available (Hochmuth et al., 2003a, 2003b). Fertilizer recommendations for vegetable crops grown on the calcareous soils of southern Miami–Dade County are currently incomplete because no calibrated soil test is available for the area (Li et al., 2006a, 2006b, 2006c, 2006d, 2006e, 2006f, 2006g, 2006h, 2006i, 2006j). In the absence of a calibrated soil test for this Florida soil type (ammonium bicarbonate–diethylene triamine penta-acetic acid extractant has been considered), fertilizer recommendations and, hence, practices are based on experience and results of whole leaf analysis and/or petiole sap testing.

UF/IFAS irrigation scheduling recommendations for vegetable crops grown with seepage irrigation are to maintain the water table at the 15- to 31-cm depth when plants are small and at the 31- to 61-cm depth when plants are fully grown. Irrigation recommendations for vegetables grown with overhead and drip irrigation include to 1) use an evapotranspiration (ET) -based target volume; 2) fine-tune volume based on soil moisture level; 3) split irrigation to limit water movement below the root zone; and 4) keep records of irrigation practices (Simonne et al., 2007). As recommended by the UF/IFAS Vegetable Fertilizer Task Force, research results on fertilizer and irrigation management developed in the context of the BMP and published in refereed journal articles since the early 2000s need to be incorporated into UF/IFAS recommendations (Cantliffe et al., 2006). Recently approved updates to UF/IFAS fertilization recommendations from the UF/IFAS Vegetable Fertilizer Task Force were to 1) adopt preliminary N recommendations for drip-irrigated grape tomato (Solanum lycopersicum var. cerasiforme); 2) report lack of efficacy of foliar-applied calcium sprays to improve strawberry yields and postharvest quality; and 3) increase by 25% N fertilization recommendation for seepage-irrigated crops to compensate for denitrification losses (UF/IFAS Plant Nutrient Oversight Committee, unpublished data).

Current methods for load measurement and available estimates

Quantifying nutrient load from vegetable production systems is the first step toward monitoring groundwater pollution in the field and understanding how each group of BMP contributes to load reduction. A nutrient load is defined as the weight of a chemical entering or leaving an area, and it is calculated as the product of the volume of water that the chemical is transported in and the concentration of the chemical in the water (Rice and Izuno, 2001). Past research has focused mostly on improving estimation of nutrient concentration, and several assumptions are often made in determining the corresponding volume of water on a per-acre basis. This is important for vegetable crops grown on raised beds because the leaching or wetted surface depends on bed compaction, width, and spacing (Farneselli et al., 2008). Load estimates may vary from simple to double based on the assumptions made on the size and shape of the wetted zone (Farneselli et al., 2008). Because nutrient concentration and size/shape of the wetted zone are equally important for in-field load determinations, they should be estimated with the same level of accuracy.

Nutrient load can be determined indirectly or directly. The indirect approaches of measuring load include nutrient flow models and nutrient balances. Nutrient flow models are important tools for evaluating the impact of nutrient leaching on water quality at the watershed level and play an important role in designing agricultural and environmental policies. Direct methods for calculating load at the field level are resin traps, soil sampling, or drainage lysimeters (Farneselli et al., 2008; Pampolino et al., 2000; Zotarelli et al., 2007). Although each of these methods has its own advantages and limits, small, in-row drainage lysimeters are emerging as a practical tool for direct load measurements (Gazula et al., 2006; Migliaccio et al., 2006; Zotarelli et al., 2008). A partial vacuum may be added to low-cost drainage lysimeters to prevent water logging without compromising the accuracy of the results (Evett et al., 2006). At 0.0013 mm, accuracy of drainage measurement was nearly two orders of magnitude better than that of the lysimeter weight measurement (1 mm), ensuring that the continuous drainage measurement may be included in the weight balances determination of ET without diminishing the accuracy of ET values (Evett et al., 2006).

Few in-field load estimates have been published for vegetables, and few of those were developed on sandy soils applicable to Florida (Table 1). Load estimates ranged from 1 to 400 kg·ha−1 of N and varied based on crops, cultural practices, and irrigation/fertilizer management, but also based on the methodology used for extrapolating load calculations to a per-hectare basis. Hence, efforts should be made to standardize protocols and methodology for in-field load estimation. In addition, the link between irrigation management and nutrient leaching shows that education on irrigation and nutrient management is central to BMP implementation. In-field load assessment should be considered a funding priority by state agencies. An increased fertilizer rate does not directly translate into an increase in load. This first requires the development of reliable methods and tools of known precision because watershed-level load simulations are poor indicators of actual field-level leaching. The effect of all fertilizer recommendations on nutrient load should be determined for all major vegetable crops through on-farm research projects in regionally appropriate production areas.

Table 1.

Published estimates of nitrogen (N) load for selected crops.

Table 1.

Zero-discharge systems

Achieving zero-discharge systems would ensure that water is kept in the root zone of vegetables. In theory, spodosols allow for a natural zero-discharge system when the spodic layer is continuous and in the absence of rain. In short, spodosols have an impermeable layer that transforms a field into a giant bathtub. When it rains, water needs to be pumped out of the field to prevent flooding. Currently, a zero-discharge system on deep sand soils does not seem technically feasible in field production (past attempts to create physical barriers of concrete or plastic have failed). By contrast, it can be done relatively simply in greenhouse production. Attempts to modify soil water-holding capacity in open fields by using organic (compost, modified corn starch, polyacrylamides) or inorganic (zeolites) amendments are economically and technically not feasible as a result of the large quantities of material needed (Bhardwaj et al., 2007; Sepaskhah and Yousefi, 2007; Sivapalan, 2006; Vachere et al., 2003).

Cover crops are often presented as an underused BMP. Cover crops may be used to compete with weeds (Linares et al., 2008), return biomass and nutrients to the soil (Muñoz-Arboleda et al., 2008; Schomberg et al., 2007), and retain pesticide residues (Potter et al., 2007). However, cover crops are not used as often as expected because more research is needed to 1) identify suitable cover crops for different seasons in Florida; 2) assess the role of a cover crop in the life cycle of crop pests (disease, insect, and virus); and 3) quantify the real capability of nutrient scavenging of each cover crop. Cost and seed availability are also cited as impediments to a broader use of cover crops. Hence, as a result of the low water-holding capacity of Florida sandy soils and unpredictable rainfall patterns, zero discharge in field production should be considered a reachable goal, but in the long term, “quasi-zero discharge” may be more realistic.

Catch ponds are sometimes used to collect excess rainfall in seepage-irrigated systems. However, ponds represent a large capital investment and permanently occupy land. The use of polyacrylamide blocks or zeolite filters located at key structures/discharge points have shown promise to trap soluble nutrients and sediments in arid environments (Zreig et al., 2007). Limited research has been conducted so far by UF/IFAS on this topic, but engineering firms have successfully used this technology on construction sites throughout Florida. However, peak volumes during storm events may be excessively large on commercial operations, thereby limiting this practice. Zero-discharge systems in mulched and drip-irrigated fields with deep sandy soils may be approachable if drip irrigation application rates can match hourly crop ET rates. This will require slight modification of existing systems (filters and pipes) and the development of ultralow-flow drippers.

Controlled-release fertilizers [CRFs (mostly for N)] should also be part of the zero-discharge approach. Currently, limited information is available on the use of CRFs for vegetables, except potato [Solanum tuberosum (Hutchinson, 2004; Pack et al., 2006; Simonne and Hutchinson, 2005)]. An ongoing project is assessing seepage-irrigated tomato and bell pepper (Capsicum annuum) responses to CRFs in southern Florida. Research on developing CRF-based fertilization programs should be supported for all the main crops grown with seepage irrigation, including potato, tomato, bell pepper, eggplant (Solanum melongena), watermelon, and cabbage (Brassica oleracea var. capitata).

Potential role of breeding and grafting on improving vegetable crop nutrient use efficiency

Together with adjustment in cultural practices, load reduction may be accomplished by using varieties selected for improved nutrient uptake characteristics. Most public breeding programs focus on developing parents for hybrids, whereas private breeding programs mostly produce industry-ready varieties. With the exception of N-efficient potato varieties from Europe, improved nutrient use efficiency (NUE) is rarely the main focus of either type of vegetable breeding programs. Overall, breeding for improved pest resistance is the main focus. By using high fertility rates in breeding programs, little emphasis is placed on “passively” selecting for high NUE varieties. Hence, public and private breeding programs will have to be committed to NUE in the parents and new commercial varieties released.

Efforts to improve NUE have been conducted in the last 40 years on food crops of worldwide importance such as wheat [Tricticum aestivum (Abad et al., 2004; Chao et al., 2007)], corn [Zea mays (Halvorson et al., 2002)], and bean [Phaseolus vulgaris (Beebe et al., 2006)] with emphasis on horticultural productivity and nutritional quality of the harvested plant part. Differences in nutrient uptake patterns among genotypes within a genus are known for many vegetable crops, including tomato (JianJun and Gabelman, 1995; O'Sullivan et al., 1974), cabbage (JinKiu et al., 2006; Tanaka and Sato, 1997), potato (Shahnazari et al., 2008; Sharifi and Zebarth, 2006; Sharifi et al., 2007), and pumpkin [Cucurbita pepo (Swiader et al., 1994)]. However, the focus of these research projects was mostly to document phenotypical differences or to improve the adaptation of current lines to areas of poor growing conditions (such as salinity or micronutrient deficiencies) rather than identify genes involved in nutrient uptake. Breeding approaches that may increase plant nutrient use efficiency include 1) anatomical modifications of root system architecture, including increased branching and number of small, absorbing roots (Beebe et al., 2006; Frith and Nichols, 1975; Muñoz-Arboleda et al., 2006; XiangRong et al., 2005); 2) chemical modification of the soil around the roots that increase the availability of nutrients [release of phosphatases that make P more available (George et al., 2005) or citrate that lower and buffer the pH near the roots (Schenk, 2006)]; 3) biochemical modification of the root surface by increasing the number of absorption sites on each root (Cuartero and Fernandez-Muñoz, 1999); and 4) understanding the regulation of genes involved in nutrient uptake (Chao et al., 2007).

With all the plant physiology knowledge developed since the 1970s and the recent progress in genomics, breeding for root systems with improved NUE may soon become a reality. It will require the commitment of UF/IFAS breeding programs and the identification of all the genes that code for the phenotype of interest. Projects should link together soil chemistry, plant biochemistry, plant physiology, and genomics. Although this type of effort may contribute to BMP adoption and improvement of water quality, the full funding of these long-term, basic projects may be beyond the scope of funding by the Florida agencies involved in the BMP program. However, these agencies could partially support these projects.

Traditionally, breeding has focused on improving the genotype of a single (open-pollinated) or two (hybrid) parents. Vegetable grafting is an innovative technique successfully practiced in Asia, parts of Europe, and the Middle East that develops a new plant by physically uniting two plants (the rootstock and the scion) through the graft (Edelstein, 2004; Lee, 2007). Resistant rootstocks, grafting methods, and procedures are being developed primarily on tomato, eggplant, and watermelon for the management of soilborne pathogens such as fusarium, verticillium, and nematodes. In addition to disease control, grafted plants have shown tolerance to environmental stresses such as low temperature and salinity (Estañ et al., 2005; Lee, 1994). Because grafted vegetables often exhibit significant yield increases as a result of vigorous growth even in the absence of disease pressure, it is possible that grafting may enhance water and nutrient uptake by plants (Khah et al., 2006; Lee, 1994; Qaryouti et al., 2007). Hence, grafting may help speed the development of nutrient- and water-efficient plants. If the commercial plant material targeted is a grafted transplant, a novel approach to plant breeding could be to separately develop hybrid rootstocks and hybrid scions. Economical analysis will have to establish the breakeven point between the environmental benefit and the cost of labor and seed associated with grafting before this technique is adopted by the industry.

Vision for the next 5 years: What does the industry need to do better?

The main technically feasible practices that could be implemented or developed in the short term include 1) switching from seepage to drip irrigation; 2) identifying adequate release pattern from CRFs for seepage-irrigated crops; and 3) developing ultralow-flow drip tapes for drip irrigation (Tables 2, 3, and 4). In theory, keeping the water in the root zone of vegetable crops could be achieved by having an adjustable flow-rate emitter (by changing operating pressure) in which flow rate could match hourly crop ET. The feasibility of achieving ultralow-flow rates (1.02 to 1.53 L·m−1·h−1) by operating current emitters at lower pressures or developing new emitters needs to be investigated. This may require the development of partnerships with irrigation supply manufacturers. Also, the effects of low pressure on uniformity and filtration requirements need to be addressed to reduce clogging risk. We believe that ultralow-flow drip irrigation is the strategy that has the greatest potential to simultaneously keep the water in the root zone of vegetable crops and reduce water use (another challenge in Florida, but not directly tied with the BMP program). The economical feasibility of implementation of each of these practices also needs to be determined. In addition, 4) real-time, continuous sensing of soil moisture status, soil EC, and nutrient concentrations; and 5) yield mapping as a basis for nutrient application and using recycled water need to be considered. In doing so, fertilizer and irrigation management needs to be considered within a production system (and not as independent variables that can be changed as needed) and the cost of each new technique needs to be related with the value of the information provided to the grower. The development of new soil nutrient sensors and yield mapping techniques offers the attractive prospective of reducing the need for soil sampling and of linking field heterogeneity to nutrient management. Real-time field data could be used as “BMP intelligence.”

Table 2.

Summary of current best management practice (BMP) research areas for vegetables grown in Florida, level of knowledge, and gaps.

Table 2.
Table 3.

Questions to and summary of vision statements by key University of Florida Institute of Food and Agricultural Science (UF/IFAS) state and county faculty with active programs in best management practices (BMP) for vegetable crops.

Table 3.
Table 4.

Strategic areas of future research for improving the quality of Florida waters, their respective approaches, and estimated chances of success.

Table 4.

Industry progress in irrigation and nutrient management in the near future is likely to depend on the general economic context (production costs, food safety issues, labor availability) and on educational programs (Simonne and Ozores-Hampton, 2006). The BMP process so far has focused on the land owner and/or on the grower. However, the commitment of the consulting and fertilizer industry to the BMP program and water quality also needs to be strengthened. Similar to what was developed for pesticides in the 1970s, a fertilizer applicator's license program coordinated by FDACS and educationally supported by UF/IFAS should be developed based on the existing Certified Crop Advisor program. In a state like Florida where UF/IFAS is not the sole direct source of information for the growers, it is essential that all segments of the vegetable industry be involved in the BMP program.

The mobile irrigation laboratories, the BMP implementation teams, and local extension offices should be supported and given the resources necessary to fully use their knowledge, experience, credibility, and connection with the growers to ensure a rapid adoption of BMP by the vegetable industry in Florida.

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    • Crossref
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  • Lee, J.M. 1994 Cultivation of grafted vegetables. I. Current status, grafting methods, and benefits HortScience 29 235 239

  • Lee, S.G. 2007 Production of high quality vegetable seedling grafts Acta Hort. 759 169 174

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006d Eggplant production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 856 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR008>.

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006i Sweet corn production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 862 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR013>.

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Contributor Notes

Corresponding author. E-mail: esimonne@ufl.edu.

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  • Lecompte, F., Bressoud, F., Pares, L. & De Bruyne, F. 2008 Root and nitrate distribution as related to the critical plant N status of a fertigated tomato crop J. Hortic. Sci. Biotechnol. 83 223 231

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  • Lee, J.M. 1994 Cultivation of grafted vegetables. I. Current status, grafting methods, and benefits HortScience 29 235 239

  • Lee, S.G. 2007 Production of high quality vegetable seedling grafts Acta Hort. 759 169 174

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006b Cabbage production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 854 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR006>.

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006c Cucumber production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 855 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR007>.

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006d Eggplant production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 856 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR008>.

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006e Okra production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 857 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR009>.

    • Search Google Scholar
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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006f Pepper production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 859 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR010>.

    • Search Google Scholar
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  • Li, Y.C., Klassen, W., O'Hair, S., Lamberts, M. & Olczyk, T. 2006g Potato production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 860 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR011>.

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  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006h Summer squash production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 861 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR012>.

    • Search Google Scholar
    • Export Citation
  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006i Sweet corn production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 862 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR013>.

    • Search Google Scholar
    • Export Citation
  • Li, Y.C., Klassen, W., Lamberts, M. & Olczyk, T. 2006j Tomato production in Miami–Dade County, Florida Univ. Florida, Inst. Food Agr. Sci., HS 858 15 Mar. 2008 <http://edis.ifas.ufl.edu/TR014>.

    • Search Google Scholar
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  • Linares, J., Scholberg, J., Boote, K., Chase, C.A., Ferguson, J.J. & McSorley, R. 2008 Use of the crop weed index to evaluate weed suppression by cover crops in organic citrus orchards HortScience 43 27 34

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Macaigne, P., Parent, L.E. & Anctil, F. 2008 Single-hole soil sampling for nitrogen in the potato hill Commun. Soil Sci. Plant Anal. 39 1486 1492

  • Migliaccio, K.W., Yuncong, L., Trafford, H. & Evans, E. 2006 A simple lysimeter for soil water sampling in south Florida Univ. Florida, Inst. Food Agr. Sci., Circ. ABE 361 15 Mar. 2008 <http://edis.ifas.ufl.edu/AE387>.

    • Search Google Scholar
    • Export Citation
  • Muñoz-Arboleda, F., Mylavarapu, R. & Hutchinson, C. 2006 Root distribution under seepage-irrigated potatoes in northeast Florida Amer. J. Potato Res. 83 463 472

  • Muñoz-Arboleda, F., Mylavarapu, R., Hutchinson, C. & Portier, K. 2008 Nitrate-nitrogen concentrations in the perched ground water under seepage-irrigated potato cropping systems J. Environ. Qual. 37 387 394

    • Crossref
    • Search Google Scholar
    • Export Citation
  • O'Sullivan, J., Gabelman, W.H. & Gerloff, G.C. 1974 Variations in efficiency of nitrogen utilization in tomatoes (Lycopersicon esculentum Mill.) grown under nitrogen stress J. Amer. Soc. Hort. Sci. 99 543 547

    • Search Google Scholar
    • Export Citation
  • Oikeh, S.O., Carsky, R.J., Kling, J.G., Chude, V.O. & Horst, W.J. 2003 Differential N uptake by maize cultivars and soil nitrate dynamics under N fertilization in West Africa Agr. Ecosyst. Environ. 100 181 191

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Olson, S.M. & Simonne, E.H. 2007 Vegetable production handbook for Florida 2007–2008 Vance Publishing Lenexa, KS

  • Pack, J.E., Hutchinson, C.M. & Simonne, E.H. 2006 Evaluation of controlled-release fertilizers for northeast Florida chip potato production J. Plant Nutr. 29 1301 1313

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pampolino, M.F., Urushiyama, T. & Hatano, R. 2000 Detection of nitrate leaching through bypass flow using pan lysimeter, suction cup, and resin capsule Soil Sci. Plant Nutr. 46 703 711

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Paudel, K.P., Adhikari, M. & Martin N.R. Jr 2004 Evaluation of broiler litter transportation in northern Alabama, USA J. Environ. Manage. 73 15 23

  • Peralta, J.M. & Stockle, C.O. 2002 Dynamics of nitrate leaching under irrigated potato rotation in Washington State: A long-term simulation study Agric. Ecosyst. Environ. 88 23 34

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Potter, T.L., Bosch, D.D., Joo, H., Schaffer, B. & Muñoz-Carpena, R. 2007 Summer cover crops reduce atrazine leaching to shallow groundwater in Southern Florida J. Environ. Qual. 36 1301 1309

    • Crossref
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