Improving Nitrogen and Phosphorus Fertilizer Use Efficiency for Florida's Horticultural Crops

in HortTechnology
View More View Less
  • 1 Soil and Water Science Department, University of Florida, P.O. Box 110290, Gainesville, FL 32611

Florida's citrus (Citrus spp.), vegetable, and turfgrass industries must improve nitrogen (N) and phosphorus (P) fertilizer use efficiency to remain sustainable in an era of emerging environmental policies designed to protect water quality. Producers have traditionally used water-soluble N and P fertilizers because they are plentiful and economical. Improving nutrient use efficiency (NUE) is being addressed through implementation of best management practices (BMPs) such as nutrient management planning, proper fertilizer material selection, better application timing and placement, and improved irrigation scheduling. Emerging technology that will aid in this effort includes increased use of enhanced efficiency fertilizers (EEFs), organic soil amendments, fertigation, and foliar fertilization. However, any new technology shown to improve NUE must be economically feasible before it can be considered a BMP. Future research in this area will aim to improve the economics of EEFs and precision fertilizer application.

Abstract

Florida's citrus (Citrus spp.), vegetable, and turfgrass industries must improve nitrogen (N) and phosphorus (P) fertilizer use efficiency to remain sustainable in an era of emerging environmental policies designed to protect water quality. Producers have traditionally used water-soluble N and P fertilizers because they are plentiful and economical. Improving nutrient use efficiency (NUE) is being addressed through implementation of best management practices (BMPs) such as nutrient management planning, proper fertilizer material selection, better application timing and placement, and improved irrigation scheduling. Emerging technology that will aid in this effort includes increased use of enhanced efficiency fertilizers (EEFs), organic soil amendments, fertigation, and foliar fertilization. However, any new technology shown to improve NUE must be economically feasible before it can be considered a BMP. Future research in this area will aim to improve the economics of EEFs and precision fertilizer application.

Florida's citrus, vegetable, ornamental, and turf growers walk a fine line as they attempt to maintain economical production while simultaneously protecting the surrounding environment from excessive nutrients. In the face of increased fertilizer cost and stringent environmental regulation, these industries have a critical need to improve nitrogen (N) and phosphorous (P) fertilizer use efficiency to remain sustainable. Plant nutrient management is intensive when producing high-value horticultural crops that demand high fertilizer and irrigation inputs. Producers cannot afford a decrease in crop volume or quality due to nutrient deficiency, especially considering the total capital outlay required to produce a crop [e.g., more than $25,000/ha for tomato (Solanum lycopersicum) production]. When applied nutrients are not taken up by the crop, fertilization efficiency decreases and unused N and P can be lost through leaching or runoff to groundwater or surface water. Total maximum daily load (TMDL) implementation in Florida will limit N and/or P loading in watersheds where horticultural crops are grown. If nutrient management practices within a watershed are not efficient enough to meet prescribed TMDLs, then the industry could face penalties that would threaten its viability in that watershed.

article image

The objective of this article is to describe general avenues and new directions that Florida's horticultural crop producers can take to improve N and P nutrient use efficiency (NUE), defined as the ratio of the amount of fertilizer nutrient taken up by the target plant to the amount applied. First, common water-soluble fertilizer (WSF) materials that have been used for decades to supply N and P to horticultural crops are characterized, and best management practices (BMPs) that are being implemented to minimize off-site nutrient loss are summarized. Second, alternative fertilizer sources and methods of application that have been shown to improve NUE are explored. Finally, high-priority research topics that will improve our knowledge about how to keep nutrients in the horticultural crop root zone are suggested.

Water-soluble N and P fertilizers

Water-soluble fertilizers dominate in Florida because they are plentiful and cost considerably less than slow or controlled-release fertilizers. A negative aspect about water-soluble N fertilizer is that it readily and rapidly leaches through Florida's sandy soils with excessive rainfall or irrigation. Five materials make up essentially the entire suite of water-soluble N fertilizers used (Table 1). Each material has unique characteristics that make it suitable or unsuitable for particular horticultural applications (Sartain and Kruse, 2001). For example, the acidifying property of ammonium sulfate makes it desirable for application to acid-loving plants such as highbush blueberry (Vaccinium corymbosum). On the other hand, urea is not suitable for application to Florida's alkaline soils due to ammonia volatilization hazard.

Table 1.

Properties of water-soluble nitrogen (N) fertilizers used in Florida commercial horticulture production.

Table 1.

Phosphorus fertilizers applied in Florida are almost entirely water-soluble materials. An exception occurs when a polymer-coated N–P–K material is used that applies a small amount of P in controlled-release form. The group of water-soluble P fertilizers used in Florida is comprised of four materials that each have unique characteristics (Table 2). They are quite versatile in their horticultural application, but there are a few instances where a particular material should not be used (Sartain and Kruse, 2001). For example, diammonium phosphate should not be applied to an alkaline soil due to volatilization of N and loss of P availability.

Table 2.

Properties of water-soluble phosphorus (P) fertilizers used in Florida commercial horticulture production.

Table 2.

The efficiency of WSFs can be enhanced by using appropriate rates, sources, application timing, and placement. Specific techniques to improve WSF efficiency in Florida's horticultural production systems are discussed in production guides (Obreza and Morgan, 2008; Olson and Simonne, 2007), and review articles (Hochmuth, 2003; Locascio, 2005), thus they will not be discussed in detail here.

BMPs to improve WSF use efficiency

In Florida, BMPs are defined as “practices based on research, field-testing, and expert review determined to be the most effective and practicable on-location means, including economic and technological considerations, for improving water quality in agricultural and urban discharges.” The formal procedure used to establish horticultural crop BMPs after the need was identified included: 1) forming a steering committee and technical work groups, 2) producing a draft BMP manual, 3) peer-review and revision, 4) holding public workshops, and 5) adopting the manual in state code. Producers who voluntarily implement BMPs receive a presumption of compliance with water quality standards and are eligible for cost-share funds to improve operations.

Florida Department of Agriculture and Consumer Services (FDACS) has published BMP manuals for sod, container nursery, vegetable, and citrus production (FDACS, 2000, 2002, 2004, 2005, 2006, 2007a, 2007b), while the Florida Department of Environmental Protection (FDEP) has produced BMP manuals for golf courses and turf/ornamental landscapes (Thomas, 2007, 2008). Most nutrient BMPs are simple, common-sense, “good housekeeping” practices. In abbreviated form, they involve: 1) educating and training field operators about how to manage fertilizer, 2) developing a nutrient management plan, 3) using appropriate fertilizer sources and formulations, 4) using application equipment that applies fertilizer to target sites, 5) properly calibrating and maintaining application equipment, 6) using precision nutrient application where appropriate, 7) avoiding high-risk fertilizer applications (such as during the rainy season), 8) splitting fertilizer applications throughout the growing season, 9) adding organic matter to the soil whenever possible, and 10) using soil moisture sensors to improve irrigation scheduling.

Enhanced efficiency fertilizers (EEFs)

The American Association of Plant Food Control Officials describes EEFs as fertilizer products with characteristics that minimize the potential of nutrient losses to the environment, as compared with “reference soluble” products (Hall, 2006). Enhanced efficiency fertilizers include slow and controlled-release materials as well as nitrification and urease inhibitors. Agronomic effectiveness of EEFs is not implied in this definition, but it is assumed. In Florida, high-volume use of EEFs in horticultural applications is limited to turfgrass, greenhouse, nursery, and landscape settings due to higher costs compared with WSF. Smaller amounts of EEFs are used in citrus replant situations and other specialty horticulture. For example, vegetable growers sometimes include slow-release N in fertilizer blends applied under plastic mulch.

Nutrient release from EEFs.

There are several modes by which nutrients are released from EEFs (Table 3). Coated fertilizers contain water-soluble N (alone or in combination with other nutrients) surrounded by an impermeable or semipermeable coating. Nutrients are released by diffusion through the coating or following degradation of the coating. Examples include sulfur-coated urea (SCU), Osmocote® (Scotts, Marysville, OH), Nutricote® (Florikan, Sarasota, FL), and Polyon® (Agrium Advanced Technologies, Sylacauga, AL). Noncoated EEFs include materials of limited water solubility that release plant-available N as they decompose chemically or microbially. Examples include ureaformaldehyde (UF), methylene urea (MU), and isobutylidene diurea (IBDU). In all cases, moisture and temperature play a significant role in determining how quickly N and other nutrients are released.

Table 3.

Properties of enhanced efficiency fertilizers used in Florida commercial horticultural production.

Table 3.

It is important for a producer to understand how a particular EEF works and to know its designed release rate before applying it in a horticultural situation. Studies evaluating EEF use in vegetable production have emphasized how a crop can suffer if nutrient release is not fast enough (Csizinszky et al., 1993; Graetz et al., 1987). Simonne and Hutchinson (2005) measured N release rates of 18 EEFs tested for utility in growing potato (Solanum tuberosum). Only three materials released N at a rate fast enough for potato production; the rest of the materials were too slow. Figure 1 shows an example of an EEF release curve that is well-matched to plant needs (Medina et al., 2008). Citriblen® fertilizer (Scotts) is formulated for use in mature citrus groves, where recommendations suggest that two-thirds of the N should be released within 110 d after applying in the spring.

Fig. 1.
Fig. 1.

Nitrogen (N) release patterns of Citriblen® (Scotts, Marysville, OH) enhanced efficiency fertilizer measured in southwestern and central Florida (Medina et al., 2008).

Citation: HortTechnology hortte 20, 1; 10.21273/HORTTECH.20.1.23

Timing of EEF application.

The goal in EEF application timing is to match the release curve with crop nutrient demand during the growing season (Schwab and Murdock, 2005). For example, newly planted citrus trees should be fertilized at planting, while established trees should receive EEF in late winter or early spring before the first spring vegetative flush and bloom. Turf and ornamental landscapes in southern Florida can receive EEF between April and September, but in northern Florida, it should only be applied between May and July (Sartain, 2007). Vegetables should be fertilized with EEFs preplant, beneath the plastic mulch if applicable (Simonne and Hochmuth, 2007). For greenhouse and nursery crops, EEFs are typically incorporated into the potting media or topdressed after planting.

Placement of EEF.

Placement (e.g., surface vs. incorporated) is important to improve NUE and decrease leaching. In an EEF placement study, Broschat (2005) measured lower N, P, and K release rates from surface-applied Osmocote® and Nutricote® fertilizers compared with placing them 10 cm deep in the potting substrate. Million et al. (2007a) found that surface application of Osmocote® to sweet viburnum (Viburnum odoratissimum) did not affect plant growth compared with incorporation, but N and P leaching losses were reduced 16% and 25%, respectively, when the EEF was surface-applied. In a field study, EEFs undergoing evaluation for long-term use on sweet orange (Citrus sinensis) trees were applied to the soil surface even if the manufacturer's instructions stated that the material should be incorporated (Obreza et al., 1999). In all cases, surface application did not detrimentally affect EEF performance, likely because it was applied within the wetted pattern of the microirrigation system that maintained a continuous moist environment on the grove floor.

Temperature and moisture effects on EEF.

Temperature and moisture can affect EEF release rate (Sartain and Kruse, 2001). In most cases, as temperature increases, nutrient release from an EEF increases. However, the temperature-release curve relationship has not been well defined in a quantitative way for many of the EEFs used in Florida. Surface-applied EEFs release nutrients more slowly than incorporated EEFs due to intermittent wetting and drying. For continuous nutrient release, EEF particles need to be continuously moist, but they do not require complete water immersion.

Horticultural performance and N leaching.

Numerous Florida studies have measured horticultural performance, and in some cases, leaching, of EEFs. Turfgrass has been the most studied crop in the past two decades. In a series of field experiments, polymer-coated ammonium sulfate and polymer-coated urea applied to bermudagrass (Cynodon dactylon), perennial ryegrass (Lolium perenne), and/or st. augustinegrass (Stenotaphrum secundatum) produced equal or better turf growth and quality ratings when compared with a standard fertilization program using WSF (Sartain, 1994c, 1995a; Varshovi and Sartain, 1993, 1996a, 1996b, 1996c). In addition, EEFs reduced N leaching losses by 50% to 75% compared with WSF (Sartain, 1992; Varshovi and Sartain, 1993). However, EEFs have not always performed better than WSF. In a large pot study, Saha et al. (2007) found that even though less N leaching occurred when st. augustinegrass was fertilized with EEF, higher plant quality was observed where WSF was used.

A typical question that a producer considering the use of EEF asks is: “Can I apply a lower fertilizer rate when using an EEF compared with a conventional WSF program and get the same response?” Environmentally enhanced fertilizer evaluation studies have been structured to answer this question by determining the rate by source interaction in full factorial experiments, but a conglomeration of results (Table 4) suggests there is no definitive answer. Of the 16 experiments summarized, six showed that a lower rate of EEF performed as well or better than a higher rate of WSF, eight showed no rate advantage to EEF, and two showed mixed results depending on the measured response. Of the six “yes” answers, five involved citrus trees and one involved vegetables. Of the eight “no” answers, three involved citrus, three involved turfgrass, and two involved vegetables.

Table 4.

Summary of Florida studies comparing enhanced efficiency fertilizers (EEFs) with water-soluble fertilizer (WSF) where it was possible to determine a rate by source interaction from a full factorial experiment.

Table 4.

N leaching from field-applied EEFs is assumed to be minimal because, by design, these materials release water-soluble N at a slow rate. Nitrogen not released to the soil remains in an insoluble form or is protected from dissolution by a coating, therefore it cannot leach all at once. Leaching from EEFs has been measured in laboratory simulations with no plants (Table 5), measured in field lysimeters containing turfgrass (Table 6), and estimated in a central Florida citrus grove on deep sandy soil (Table 7). In all cases, N leaching from water-soluble N fertilizer was greater than leaching from EEFs. Nitrogen leaching from containerized plant production has also been measured (Broschat 1995; Table 8). In one experiment, plant growth substrate influenced the relative amount of fertilizer N that leached. Less nitrate leached from EEFs compared with WSF when plants were grown in pine bark–peat–sand media. When the media was sandy field soil, nitrate leaching did not differ between fertilizer types. Phosphorus leaching from EEFs was always significantly lower compared with WSF, regardless of potting substrate type. Plant growth was as good or better with EEFs compared with WSF.

Table 5.

Leaching of water-soluble and enhanced efficiency nitrogen (N) fertilizer applied to a sandy Entisol followed by exposure to simulated rainfall events.

Table 5.
Table 6.

Leaching of nitrogen (N) from water-soluble and enhanced efficiency fertilizer (EEF) sources 125 d after applying N fertilizer at a rate of 2 lb/1000 ft2 (97.6 kg·ha−1) to ryegrass (J.B. Sartain, unpublished data).

Table 6.
Table 7.

Estimated annual nitrate-nitrogen (NO3-N) leached below the root zone of a central Florida citrus grove planted on deep sandy soil and treated with three methods of N fertilization. Data represent the mean of a 2-year period (Paramasivam et al., 2001). Quadratic regressions of annual NO3-N leached versus N rate for each fertilization method were significant at P < 0.05.

Table 7.
Table 8.

Container-grown foliage (peace lily) plant size and relative amount of nitrate-nitrogen (NO3-N) and orthophosphate-phosphorus (PO4-P) leached 6 months after enhanced efficiency fertilizer (EEF) or water-soluble fertilizer (WSF) application to pine bark-peat-sand media or sandy field soil (Broschat, 1995).

Table 8.

Natural organic soil amendments and fertilizers

This grouping includes less processed materials like animal manure and biosolids that may or may not have a guaranteed nutrient analysis, plus more refined materials like fish and seaweed emulsions that are sold as commercial products with a guaranteed analysis. If an organic material is included as part of a nutrient management plan, the mineralization rate must be considered when determining the rate to apply (Treadwell et al., 2007). Organic matter decomposes relatively quickly in Florida's warm and humid climate. For example, Hanselman et al. (2004) showed that roughly half of the N in biosolids and two-thirds of the N in poultry (layer) manure mineralized to plant-available forms during the first year after application at several Florida locations. The N mineralization was front-loaded for poultry manure and biosolids (i.e., most of the N became plant-available in the first month after application, followed by a gradual release of the remainder during the subsequent 11 months). A similar release of N from seabird guano, fish powder, feather meal, and blood meal was observed by Hartz and Johnstone (2006). In their study, most of the applied N mineralized within 2 weeks.

Fertigation

Nutrient use efficiency can be increased by substituting fertigation for pre-plant WSF application in vegetable production. When bell pepper (Capsicum annuum) yield was used an indicator, N use efficiency increased as the proportion of N applied via fertigation increased [Table 9 (Shaw et al., 1996)]. Increased yield implies more N in the fruit per unit area, hence less potential leaching. Additional benefits of fertigation for vegetable production are summarized by Locascio (2005).

Table 9.

Bell pepper marketable yield response to four preplant/fertigation nitrogen (N) fertilizer combinations applied under plastic mulch to a sandy Ultisol (Shaw et al., 1996).

Table 9.

Fertigation frequency for vegetables can vary from daily application to one fertigation per week (Simonne and Hochmuth, 2007). No advantage to daily versus weekly fertigation has been observed with proper irrigation management. Nitrogen fertilizer application is most precise if rates are determined by crop growth and resulting nutrient demand. For example, N rates for tomato and bell pepper begin at 0.5 lb/acre per day during the early part of the season and increase to 2.0 lb/acre per day at peak demand.

Citrus trees do not appear to be sensitive to fertigation application frequency. This characteristic allows wide flexibility when developing a fertigation schedule. For example, the 1-year growth response of newly planted citrus trees in Gainesville, FL, did not differ when fertigated 30, 10, or 5 times at the same total N rate (Willis et al., 1991). Growth observed with fertigation did not differ from that observed with dry granular fertilizer applied five times in 1 year. Fertigation frequency also was not a factor when applied to 6-year-old lysimeter-grown trees in Lake Alfred, FL [Table 10 (Syvertsen and Jifon, 2001)]. Neither N uptake efficiency nor the relative amount of applied N that leached was significantly different when comparing about 80 fertigations per year with about 12 per year.

Table 10.

Influence of the number of fertigations applied to 6-year-old sweet orange trees growing in lysimeter tanks on the relative amount of nitrogen (N) leached and on N use efficiency (Syvertsen and Jifon, 2001).

Table 10.

Horticultural plant response to fertigation is as good or better than the response observed with well-managed dry soluble fertilization. In either case, irrigation (and sometimes drainage) water management is critical for success. Nitrogen leaching following fertigation can be minimized if the crop is not over-irrigated. It cannot be overemphasized how important irrigation duration is when fertigating. Although fertigation is sometimes referred to as “spoon feeding,” in this case, the “food” is water-soluble plant nutrients that can easily be driven beneath the plant root zone if too much water follows the fertilizer pulse (Simonne et al., 2003). It is true that fertigation prevents a large mass of nutrients from being leached in a single day (as could occur when heavy rain follows a dry fertilizer application), but leaching can still occur in smaller increments if irrigation management is poor. An interesting result of the study summarized in Table 10 was that even in a lysimeter with carefully controlled irrigation and a confined root system, about half of the N applied via fertigation leached past the root zone.

Table 7 shows an example that is contrary to the principle outlined above. Irrigation scheduling in the test citrus grove was optimal, yet more N leached in the fertigation treatment compared with dry soluble fertilizer applications. The authors of this study (Paramasivam et al., 2001) explained that more N leaching occurred with fertigation “purely because of unexpected prolonged irrigation or unexpected high rainfall following certain fertigation events in both years.”

Foliar fertilization with N and P

Citrus.

The amount of plant nutrients that can be taken up through the leaves of a citrus tree is very small. However, there are special cases where foliar application of N and/or P is justified. It must be recognized that a positive response may be due to additional effects of the materials on tree physiology beyond simple enhancement of tree nutrition.

Forms of urea are available that can be readily absorbed by citrus leaves. Foliar urea sprays applied during the winter have enhanced the number of flowers and yield of ‘Valencia’ sweet oranges (Albrigo, 1999). After cool temperatures or drought stress have occurred, applying 50 to 60 lb/acre of urea can enhance flower bud induction and may increase fruit yield. Maximum penetration of urea into citrus leaves occurs within 12 to 24 h after spray application (Orbovic et al., 2001). Optimum conditions for foliar uptake include air temperature between 77 and 88 °F, high relative humidity, and spray solution with a pH between 7 and 8 to prevent urea breakdown. Under favorable environmental conditions, roughly half of foliar-applied urea penetrates the leaves, while most of the other half is lost through volatilization. The rate of foliar-applied N should be considered as part of the total annual N rate applied to the grove. For example, a foliar spray of 50 lb/acre of urea applies 23 lb/acre of N. If the fertilization plan calls for a total of 180 lb/acre per year of N, only 157 lb/acre should be included in the soil-applied fertilizer program. In Florida citrus production areas where groundwater nitrate contamination exists or is seen as a potential problem, urea sprays should be evaluated to provide a portion of the tree N requirements, especially during the summer months when leaching potential is the greatest.

Citrus leaves are extremely impervious to phosphate (PO43-) (Lovatt and Mikkelson, 2006). Conversely, phosphite (PO33-) is more readily absorbed into plant tissue, and once inside the plant, it remains stable. Phosphite does not readily convert to phosphate in the plant, therefore the nutritional value of absorbed PO33- is uncertain. However, phosphite is officially recognized by FDACS as a source of P for crops. In Florida, a prebloom foliar application of 2.6 qt/acre of 28% P2O5 as potassium phosphate (K3PO3) to ‘Valencia’ sweet oranges significantly increased flower number, fruit yield, and total soluble solids yield compared with an untreated control (Albrigo, 1999). These results suggest that the effect of phosphite was not due to the molecule's fungicidal attributes, but to other growth-stimulating properties.

Other horticultural crops.

Foliar applications of N and P are not recommended for vegetable production because leaves cannot absorb sufficient quantities to correct a deficiency, and leaf burn is likely if this is attempted (Simonne and Hochmuth, 2007). This principle also applies to ornamental plants and turfgrass.

Example cost comparisons of EEF versus WSF programs

Citrus.

Although coated EEFs performed very well in a 6-year trial comparing them with a standard WSF program (1991–96), they would not have been economically feasible for commercial production. The EEF materials evaluated would have cost three to four times as much to use as WSF, even when the lower application cost was factored in (Obreza et al., 1999; Table 11). Extra yield obtained by using EEF did not nearly make up for the higher fertilizer cost.

Table 11.

Cost of six fertilizer programs (five enhanced efficiency fertilizers and one water-soluble fertilizer) applied to young ‘Valencia’ sweet orange trees from 1991 through 1996 compared with cumulative lb soluble solids yield and gross monetary return (Obreza et al., 1999).

Table 11.

Vegetables.

A potato production study (Simonne and Hutchinson, 2005) determined that the cost of a water-soluble N fertilization program in most years would fall between $72/ha and $158/ha. Estimated EEF program cost would be about $20/ha to $195/ha more than the most expensive soluble N cost. This extra cost could be offset by reduced application cost and/or providing cost-share for the use of EEF.

How irrigation affects fertilizer use efficiency

Irrigation effects on fertilizer NUE for vegetable production were summarized by Hochmuth (2003) and Locascio (2005), and for citrus production by Obreza and Morgan (2008). Fertilizer use efficiency of container-grown ornamental production was improved by changing the irrigation and/or fertilization methods (Yeager and Henley, 2004). One change involved the conversion of overhead irrigation to microirrigation or capillary mat/wick irrigation. The other change involved the use of EEFs [Osmocote®, Nutricote®, Multicote® (Haifa Chemicals, Haifa, Israel), and Polyon®] with overhead irrigation. During a 4-year period, the growth index of peace lily (Spathiphyllum spp.) was about the same regardless of EEF source. However, the nitrate-N concentration in the groundwater 4 ft below the ground surface of the shadehouse decreased as a result of EEF use (Fig. 2). In another study involving containerized production of Osmocote®-fertilized sweet viburnum, excessive irrigation (double the required rate) decreased plant growth, increased runoff volume from the nursery, increased N loss in runoff by 21% to 34%, and increased P loss in runoff by 28% to 38% (Million et al., 2007b).

Fig. 2.
Fig. 2.

Effect of nitrogen (N) fertilizer type and application method on groundwater nitrate-N concentration beneath ornamental plant production during a 4-year period (Yeager and Henley, 2004); EEF = enhanced efficiency fertilizer, 1 mg·L−1 = 1 ppm.

Citation: HortTechnology hortte 20, 1; 10.21273/HORTTECH.20.1.23

Future research needs

Despite numerous improvements in fertilizer use efficiency that have occurred during the past several decades, further advancement is possible if research is undertaken on the following aspects of fertilizer use: 1) develop a short-term procedure to verify the nutrient release period claimed on EEF labels, 2) evaluate nutrient leaching characteristics of EEF materials applied in the field and greenhouse, 3) conduct an economic study of EEF use that determines the value of the environmental benefit, 4) improve irrigation scheduling techniques, and 5) develop new technology for precision nutrient application.

Conclusion

The efficiency of WSF application to Florida's horticultural crops has been enhanced by using appropriate rates, sources, application timing, and placement. Producers who implement contemporary BMPs are improving NUE to a greater extent due to the synergistic effect of commodity-oriented nutrient management practices joined in a holistic program. The next steps for producers to take include greater use of EEFs, wider adoption of fertigation, application of foliar fertilizers where appropriate, and more precise irrigation scheduling. Enhanced efficiency fertilizers hold great promise to improve NUE even more, but additional research on characterization, plant response, environmental effects, and economics is needed before EEF use can be established as a BMP.

Literature cited

  • Albrigo, L.G. 1999 Effects of foliar applications of urea or Nutriphite on flowering and yields of Valencia orange trees Proc. Florida State Hort. Soc. 112 1 4

    • Search Google Scholar
    • Export Citation
  • Alva, A.K. & Tucker, D.P.H. 1993 Evaluation of a resin-coated nitrogen fertilizer for young citrus trees on a deep sand Proc. Florida State Hort. Soc. 106 4 8

    • Search Google Scholar
    • Export Citation
  • Alva, A.K. & Paramasivam, S. 1998 Nitrogen management for high yield and quality of citrus in sandy soils Soil Sci. Soc. Amer. J. 62 1335 1342

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Boman, B.J. 1993 A comparison of controlled-release to conventional fertilizer on mature ‘Marsh’ grapefruit Proc. Florida State Hort. Soc. 106 1 4

    • Search Google Scholar
    • Export Citation
  • Broschat, T.K. 1995 Nitrate, phosphate, and potassium leaching from container-grown plants fertilized by several methods HortScience 30 74 77

  • Broschat, T.K. 2005 Rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus, and potassium from two controlled-release fertilizers under different substrate environments HortTechnology 15 332 335

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Csizinszky, A.A., Stanley, C.D. & Clark, G.A. 1993 Evaluation of controlled-release urea for fresh market tomato Proc. Florida State Hort. Soc. 106 183 187

    • Search Google Scholar
    • Export Citation
  • Ferguson, J.J. & Davies, F.S. 1995 Fertilization of young citrus trees with controlled-release fertilizers Proc. Florida State. Hort. Soc. 108 156 160

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2000 Water quality/quantity BMPs for Indian River area citrus groves 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_IndianRiverCitrus2000.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2002 Nitrogen best management practices (BMPs) for Florida ridge citrus 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_RidgeCitrus2002.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2004 Best management practices for citrus groves in the Peace River and Manasota Basins 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_PeaceRiverCitrus2004.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2005 Water quality/quantity best management practices for Florida vegetable and agronomic crops 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_VeggieAgroCrops2005.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2006 Best management practices for Gulf citrus. Publ. No. 5M–7.005.03.06 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_GulfCitrus2005.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2007a Water quality/quantity best management practices for Florida sod. Publ. No. P 01330 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_FloridaSod2008.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2007b Water quality/quantity best management practices for Florida container nurseries. Publ. No. P 01267 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_FloridaContainerNurseries2007.pdf>.

    • Search Google Scholar
    • Export Citation
  • Graetz, D.A., Bottcher, A.B., Locascio, S.J. & Campbell, K.L. 1987 Tomato yield and nitrogen recovery as influenced by irrigation method, nitrogen source and mulch HortScience 22 27 29

    • Search Google Scholar
    • Export Citation
  • Hall, B. 2006 Enhanced efficiency fertilizers: Labeling, regulation, and monitoring 23 Apr. 2009 <http://www.aapfco.org/AACO%202006/AAPFCO%20SR%20Reg%2006.ppt>.

    • Search Google Scholar
    • Export Citation
  • Hanselman, T.A., Graetz, D.A. & Obreza, T.A. 2004 A comparison of in situ methods for measuring net nitrogen mineralization rates of organic soil amendments J. Environ. Qual. 33 1098 1105

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hartz, T.K. & Johnstone, P.R. 2006 Nitrogen availability from high-nitrogen containing–organic fertilizers HortTechnology 16 39 42

  • Hochmuth, G.J. 2003 Progress in mineral nutrition and nutrient management for vegetable crops in the last 25 years HortScience 38 999 1003

  • Hutchinson, C., Simonne, E., Solano, P., Meldrum, J. & Livingston-Way, P. 2003 Testing of controlled-release fertilizer programs for seep irrigated irish potato production J. Plant Nutr. 26 1709 1723

    • Search Google Scholar
    • Export Citation
  • Locascio, S.J. 2005 Management of irrigation for vegetables: Past, present, and future HortTechnology 15 482 485

  • Locascio, S.J. & Alligood, M.R. 1992 Nitrogen and potassium source and N rate for drip-irrigated pepper Proc. Florida State Hort. Soc. 105 323 325

  • Lovatt, C.J. & Mikkelson, R.L. 2006 Phosphite fertilizers: What are they? Can you use them? What can they do? Better Crops Plant Food 90 4 11 13

  • Medina, L.C., Obreza, T.A., Sartain, J.B. & Rouse, R.E. 2008 Nitrogen release patterns of a mixed controlled-release fertilizer and its components HortTechnology 18 475 480

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Million, J., Yeager, T. & Albano, J. 2007a Effects of container spacing practice and fertilizer placement on runoff from overhead-irrigated sweet viburnum J. Environ. Hort. 25 61 72

    • Search Google Scholar
    • Export Citation
  • Million, J., Yeager, T. & Albano, J. 2007b Consequences of excessive overhead irrigation on runoff during container production of sweet viburnum J. Environ. Hort. 25 117 125

    • Search Google Scholar
    • Export Citation
  • Obreza, T.A. 1993 Program fertilization for establishment of orange trees J. Prod. Agr. 6 546 552

  • Obreza T.A. & Morgan K.T. 2008 Nutrition of Florida citrus trees 2nd ed Univ. Florida, Inst. Food Agr. Sci., Soil Water Sci. Dept. SL253 23 Apr. 2009 <http://edis.ifas.ufl.edu/SS478>.

    • Search Google Scholar
    • Export Citation
  • Obreza, T.A. & Rouse, R.E. 2006 Long-term response of ‘Hamlin’ orange trees to controlled-release nitrogen fertilizers HortScience 41 423 426

  • Obreza, T.A., Rouse, R.E. & Sherrod, J.B. 1999 Economics of controlled-release fertilizer use on young citrus trees J. Prod. Agr. 12 69 73

  • Olson, S.M. & Simonne, E. 2007 Vegetable production guide for Florida Univ., Florida, Inst. Food Agr. Sci., Hort Sci. Dept. HS710 23 Apr. 2009 <http://edis.ifas.ufl.edu/features/handbooks/vegetableguide.html>.

    • Search Google Scholar
    • Export Citation
  • Orbovic, V., Achor, D., Petracek, P. & Syvertsen, J.P. 2001 Air temperature, humidity, and leaf age affect penetration of urea through grapefruit leaf cuticles J. Amer. Soc. Hort. Sci. 126 44 50

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Paramasivam, S., Alva, A.K., Fares, A. & Sajwan, K.S. 2001 Estimation of nitrate leaching in an Entisol under optimum citrus production Soil Sci. Soc. Amer. J. 65 914 921

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Paramasivam, S. & Alva, A.K. 1997 Leaching of nitrogen forms from controlled-release nitrogen fertilizers Commun. Soil Sci. Plant Anal. 28 1663 1674

  • Saha, S.K., Trenholm, L.E. & Unruh, J.B. 2007 Effect of fertilizer source on nitrate leaching and st. augustinegrass turfgrass quality HortScience 42 1478 1481

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1992 Relative nitrogen leaching losses from selected slow-release nitrogen sources 131 136 Freeman T.E. Turfgrass research in Florida. Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1993 Comparative growth rate and quality response of bermudagrass and ryegrass to various sources of slow-release N fertilizer 77 81 Cisar J.L. & Haydu J.J. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994a Bermudagrass growth and quality response to poly-S materials 51 63 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994b Controlled-release nitrogen sources for cool and warm season grasses 95 103 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994c Effects of Multicote materials on ryegrass growth and quality 110 115 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1995a St. Augustinegrass growth response to controlled-release blends 57 70 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1995b Warm and cool season turfgrass response to controlled-release nitrogen 165 174 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1996a Response of ryegrass to controlled-release nitrogen sources 190 192 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1996b Response of bermudagrass to controlled-release nitrogen sources 212 214 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 2007 General recommendations for fertilization of turfgrasses on Florida soils Univ. Florida, Inst. Food Agr. Sci., Coop. Ext. Serv. SL21 23 Apr. 2009 <http://edis.ifas.ufl.edu/LH014>.

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. & Kruse, J.K. 2001 Selected fertilizers used in turfgrass fertilization Univ. Florida, Inst. Food Agr. Sci., Soil Water Sci. Dept. Circ. 1262 23 Apr. 2009 <http://edis.ifas.ufl.edu/SS318>.

    • Search Google Scholar
    • Export Citation
  • Schwab, G.J. & Murdock, L.W. 2005 Nitrogen transformation inhibitors and controlled-release urea Univ. Kentucky Coop. Ext. Serv. AGR185

  • Shaw, N.L., Hochmuth, G.J. & Hanlon, E.A. 1996 N fertilization management for drip-irrigated bell pepper (Capsicum annuum L.) Proc. Florida State Hort. Soc. 109 136 141

    • Search Google Scholar
    • Export Citation
  • Simonne, E. & Hutchinson, C.M. 2005 Controlled-release fertilizers for vegetable production in the era of best management practices: Teaching new tricks to an old dog HortTechnology 15 36 46

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Simonne, E.H. & Hochmuth, G.J. 2007 Soil and fertilizer management for vegetable production in Florida Univ. Florida, Inst. Food Agr. Sci., Hort. Sci. Dept. HS711 23 Apr. 2009 <http://edis.ifas.ufl.edu/CV101>.

    • Search Google Scholar
    • Export Citation
  • Simonne, E.H., Studstill, D.W., Hochmuth, R.C., McAvoy, G., Dukes, M.D. & Olson, S. 2003 Visualization of water movement in mulched beds with injections of dye with drip irrigation Proc. Florida State Hort. Soc. 116 88 91

    • Search Google Scholar
    • Export Citation
  • Syvertsen, J.P. & Jifon, J.L. 2001 Frequent fertigation does not affect citrus tree growth, fruit yield, nitrogen uptake, and leaching losses Proc. Florida State Hort. Soc. 114 88 93

    • Search Google Scholar
    • Export Citation
  • Thomas M. 2007 Best management practices for the enhancement of environmental quality on Florida golf courses 8 July 2009 <http://www.dep.state.fl.us/water/nonpoint/docs/nonpoint/glfbmp07.pdf>.

    • Search Google Scholar
    • Export Citation
  • Thomas M. 2008 Florida friendly best management practices for protection of water resources by the green industries 8 July 2009 <http://www.dep.state.fl.us/water/nonpoint/docs/nonpoint/grn-ind-bmp-en-12-2008.pdf>.

    • Search Google Scholar
    • Export Citation
  • Treadwell, D.D., Hochmuth, G.J., Hochmuth, R.C., Simonne, E.H., Davis, L.L., Laughlin, W.L., Li, Y., Olczyk, T., Sprenkel, R.K. & Osborne, L.S. 2007 Nutrient management in organic greenhouse herb production: Where are we now? HortTechnology 17 461 466

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1993 Growth, N uptake, and leaching characteristics of polymer-coated urea and ammonium sulfate applied to bermudagrass 59 67 Cisar J.L. & Haydu J.J. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996a Nitrogen uptake of Tifway bermudagrass in response to polymer-coated ammonium sulfate 149 152 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996b Comparative growth of Tifgreen bermudagrass in response to golf greens grade polymer-coated ammonium sulfate and urea 153 159 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996c Nitrogen uptake of Tifgreen bermudagrass in response to golf greens grade polymer-coated ammonium sulfate 171 174 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Wang, F.L. & Alva, A.K. 1996 Leaching of nitrogen from slow-release urea sources in sandy soils Soil Sci. Soc. Amer. J. 60 1454 1458

  • Willis, L.E., Davies, F.S. & Graetz, D.A. 1991 Fertigation and growth of young ‘Hamlin’ orange trees in Florida HortScience 26 106 109

  • Yeager, T.H. & Henley, R.W. 2004 Irrigation and fertilization for minimal environmental impact Acta Hort. 638 233 240

  • Zekri, M. & Koo, R.C.J. 1992 Use of controlled-release fertilizers for young citrus trees Scientia Hort. 49 233 241

Contributor Notes

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

  • View in gallery

    Nitrogen (N) release patterns of Citriblen® (Scotts, Marysville, OH) enhanced efficiency fertilizer measured in southwestern and central Florida (Medina et al., 2008).

  • View in gallery

    Effect of nitrogen (N) fertilizer type and application method on groundwater nitrate-N concentration beneath ornamental plant production during a 4-year period (Yeager and Henley, 2004); EEF = enhanced efficiency fertilizer, 1 mg·L−1 = 1 ppm.

  • Albrigo, L.G. 1999 Effects of foliar applications of urea or Nutriphite on flowering and yields of Valencia orange trees Proc. Florida State Hort. Soc. 112 1 4

    • Search Google Scholar
    • Export Citation
  • Alva, A.K. & Tucker, D.P.H. 1993 Evaluation of a resin-coated nitrogen fertilizer for young citrus trees on a deep sand Proc. Florida State Hort. Soc. 106 4 8

    • Search Google Scholar
    • Export Citation
  • Alva, A.K. & Paramasivam, S. 1998 Nitrogen management for high yield and quality of citrus in sandy soils Soil Sci. Soc. Amer. J. 62 1335 1342

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Boman, B.J. 1993 A comparison of controlled-release to conventional fertilizer on mature ‘Marsh’ grapefruit Proc. Florida State Hort. Soc. 106 1 4

    • Search Google Scholar
    • Export Citation
  • Broschat, T.K. 1995 Nitrate, phosphate, and potassium leaching from container-grown plants fertilized by several methods HortScience 30 74 77

  • Broschat, T.K. 2005 Rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus, and potassium from two controlled-release fertilizers under different substrate environments HortTechnology 15 332 335

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Csizinszky, A.A., Stanley, C.D. & Clark, G.A. 1993 Evaluation of controlled-release urea for fresh market tomato Proc. Florida State Hort. Soc. 106 183 187

    • Search Google Scholar
    • Export Citation
  • Ferguson, J.J. & Davies, F.S. 1995 Fertilization of young citrus trees with controlled-release fertilizers Proc. Florida State. Hort. Soc. 108 156 160

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2000 Water quality/quantity BMPs for Indian River area citrus groves 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_IndianRiverCitrus2000.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2002 Nitrogen best management practices (BMPs) for Florida ridge citrus 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_RidgeCitrus2002.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2004 Best management practices for citrus groves in the Peace River and Manasota Basins 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_PeaceRiverCitrus2004.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2005 Water quality/quantity best management practices for Florida vegetable and agronomic crops 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_VeggieAgroCrops2005.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2006 Best management practices for Gulf citrus. Publ. No. 5M–7.005.03.06 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_GulfCitrus2005.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2007a Water quality/quantity best management practices for Florida sod. Publ. No. P 01330 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_FloridaSod2008.pdf>.

    • Search Google Scholar
    • Export Citation
  • Florida Department of Agriculture and Consumer Services 2007b Water quality/quantity best management practices for Florida container nurseries. Publ. No. P 01267 8 July 2009 <http://www.floridaagwaterpolicy.com/PDF/Bmps/Bmp_FloridaContainerNurseries2007.pdf>.

    • Search Google Scholar
    • Export Citation
  • Graetz, D.A., Bottcher, A.B., Locascio, S.J. & Campbell, K.L. 1987 Tomato yield and nitrogen recovery as influenced by irrigation method, nitrogen source and mulch HortScience 22 27 29

    • Search Google Scholar
    • Export Citation
  • Hall, B. 2006 Enhanced efficiency fertilizers: Labeling, regulation, and monitoring 23 Apr. 2009 <http://www.aapfco.org/AACO%202006/AAPFCO%20SR%20Reg%2006.ppt>.

    • Search Google Scholar
    • Export Citation
  • Hanselman, T.A., Graetz, D.A. & Obreza, T.A. 2004 A comparison of in situ methods for measuring net nitrogen mineralization rates of organic soil amendments J. Environ. Qual. 33 1098 1105

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hartz, T.K. & Johnstone, P.R. 2006 Nitrogen availability from high-nitrogen containing–organic fertilizers HortTechnology 16 39 42

  • Hochmuth, G.J. 2003 Progress in mineral nutrition and nutrient management for vegetable crops in the last 25 years HortScience 38 999 1003

  • Hutchinson, C., Simonne, E., Solano, P., Meldrum, J. & Livingston-Way, P. 2003 Testing of controlled-release fertilizer programs for seep irrigated irish potato production J. Plant Nutr. 26 1709 1723

    • Search Google Scholar
    • Export Citation
  • Locascio, S.J. 2005 Management of irrigation for vegetables: Past, present, and future HortTechnology 15 482 485

  • Locascio, S.J. & Alligood, M.R. 1992 Nitrogen and potassium source and N rate for drip-irrigated pepper Proc. Florida State Hort. Soc. 105 323 325

  • Lovatt, C.J. & Mikkelson, R.L. 2006 Phosphite fertilizers: What are they? Can you use them? What can they do? Better Crops Plant Food 90 4 11 13

  • Medina, L.C., Obreza, T.A., Sartain, J.B. & Rouse, R.E. 2008 Nitrogen release patterns of a mixed controlled-release fertilizer and its components HortTechnology 18 475 480

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Million, J., Yeager, T. & Albano, J. 2007a Effects of container spacing practice and fertilizer placement on runoff from overhead-irrigated sweet viburnum J. Environ. Hort. 25 61 72

    • Search Google Scholar
    • Export Citation
  • Million, J., Yeager, T. & Albano, J. 2007b Consequences of excessive overhead irrigation on runoff during container production of sweet viburnum J. Environ. Hort. 25 117 125

    • Search Google Scholar
    • Export Citation
  • Obreza, T.A. 1993 Program fertilization for establishment of orange trees J. Prod. Agr. 6 546 552

  • Obreza T.A. & Morgan K.T. 2008 Nutrition of Florida citrus trees 2nd ed Univ. Florida, Inst. Food Agr. Sci., Soil Water Sci. Dept. SL253 23 Apr. 2009 <http://edis.ifas.ufl.edu/SS478>.

    • Search Google Scholar
    • Export Citation
  • Obreza, T.A. & Rouse, R.E. 2006 Long-term response of ‘Hamlin’ orange trees to controlled-release nitrogen fertilizers HortScience 41 423 426

  • Obreza, T.A., Rouse, R.E. & Sherrod, J.B. 1999 Economics of controlled-release fertilizer use on young citrus trees J. Prod. Agr. 12 69 73

  • Olson, S.M. & Simonne, E. 2007 Vegetable production guide for Florida Univ., Florida, Inst. Food Agr. Sci., Hort Sci. Dept. HS710 23 Apr. 2009 <http://edis.ifas.ufl.edu/features/handbooks/vegetableguide.html>.

    • Search Google Scholar
    • Export Citation
  • Orbovic, V., Achor, D., Petracek, P. & Syvertsen, J.P. 2001 Air temperature, humidity, and leaf age affect penetration of urea through grapefruit leaf cuticles J. Amer. Soc. Hort. Sci. 126 44 50

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Paramasivam, S., Alva, A.K., Fares, A. & Sajwan, K.S. 2001 Estimation of nitrate leaching in an Entisol under optimum citrus production Soil Sci. Soc. Amer. J. 65 914 921

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Paramasivam, S. & Alva, A.K. 1997 Leaching of nitrogen forms from controlled-release nitrogen fertilizers Commun. Soil Sci. Plant Anal. 28 1663 1674

  • Saha, S.K., Trenholm, L.E. & Unruh, J.B. 2007 Effect of fertilizer source on nitrate leaching and st. augustinegrass turfgrass quality HortScience 42 1478 1481

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1992 Relative nitrogen leaching losses from selected slow-release nitrogen sources 131 136 Freeman T.E. Turfgrass research in Florida. Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1993 Comparative growth rate and quality response of bermudagrass and ryegrass to various sources of slow-release N fertilizer 77 81 Cisar J.L. & Haydu J.J. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994a Bermudagrass growth and quality response to poly-S materials 51 63 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994b Controlled-release nitrogen sources for cool and warm season grasses 95 103 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1994c Effects of Multicote materials on ryegrass growth and quality 110 115 Dudeck A.E. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1995a St. Augustinegrass growth response to controlled-release blends 57 70 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1995b Warm and cool season turfgrass response to controlled-release nitrogen 165 174 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1996a Response of ryegrass to controlled-release nitrogen sources 190 192 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 1996b Response of bermudagrass to controlled-release nitrogen sources 212 214 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. 2007 General recommendations for fertilization of turfgrasses on Florida soils Univ. Florida, Inst. Food Agr. Sci., Coop. Ext. Serv. SL21 23 Apr. 2009 <http://edis.ifas.ufl.edu/LH014>.

    • Search Google Scholar
    • Export Citation
  • Sartain, J.B. & Kruse, J.K. 2001 Selected fertilizers used in turfgrass fertilization Univ. Florida, Inst. Food Agr. Sci., Soil Water Sci. Dept. Circ. 1262 23 Apr. 2009 <http://edis.ifas.ufl.edu/SS318>.

    • Search Google Scholar
    • Export Citation
  • Schwab, G.J. & Murdock, L.W. 2005 Nitrogen transformation inhibitors and controlled-release urea Univ. Kentucky Coop. Ext. Serv. AGR185

  • Shaw, N.L., Hochmuth, G.J. & Hanlon, E.A. 1996 N fertilization management for drip-irrigated bell pepper (Capsicum annuum L.) Proc. Florida State Hort. Soc. 109 136 141

    • Search Google Scholar
    • Export Citation
  • Simonne, E. & Hutchinson, C.M. 2005 Controlled-release fertilizers for vegetable production in the era of best management practices: Teaching new tricks to an old dog HortTechnology 15 36 46

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Simonne, E.H. & Hochmuth, G.J. 2007 Soil and fertilizer management for vegetable production in Florida Univ. Florida, Inst. Food Agr. Sci., Hort. Sci. Dept. HS711 23 Apr. 2009 <http://edis.ifas.ufl.edu/CV101>.

    • Search Google Scholar
    • Export Citation
  • Simonne, E.H., Studstill, D.W., Hochmuth, R.C., McAvoy, G., Dukes, M.D. & Olson, S. 2003 Visualization of water movement in mulched beds with injections of dye with drip irrigation Proc. Florida State Hort. Soc. 116 88 91

    • Search Google Scholar
    • Export Citation
  • Syvertsen, J.P. & Jifon, J.L. 2001 Frequent fertigation does not affect citrus tree growth, fruit yield, nitrogen uptake, and leaching losses Proc. Florida State Hort. Soc. 114 88 93

    • Search Google Scholar
    • Export Citation
  • Thomas M. 2007 Best management practices for the enhancement of environmental quality on Florida golf courses 8 July 2009 <http://www.dep.state.fl.us/water/nonpoint/docs/nonpoint/glfbmp07.pdf>.

    • Search Google Scholar
    • Export Citation
  • Thomas M. 2008 Florida friendly best management practices for protection of water resources by the green industries 8 July 2009 <http://www.dep.state.fl.us/water/nonpoint/docs/nonpoint/grn-ind-bmp-en-12-2008.pdf>.

    • Search Google Scholar
    • Export Citation
  • Treadwell, D.D., Hochmuth, G.J., Hochmuth, R.C., Simonne, E.H., Davis, L.L., Laughlin, W.L., Li, Y., Olczyk, T., Sprenkel, R.K. & Osborne, L.S. 2007 Nutrient management in organic greenhouse herb production: Where are we now? HortTechnology 17 461 466

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1993 Growth, N uptake, and leaching characteristics of polymer-coated urea and ammonium sulfate applied to bermudagrass 59 67 Cisar J.L. & Haydu J.J. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996a Nitrogen uptake of Tifway bermudagrass in response to polymer-coated ammonium sulfate 149 152 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996b Comparative growth of Tifgreen bermudagrass in response to golf greens grade polymer-coated ammonium sulfate and urea 153 159 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Varshovi, A.A. & Sartain, J.B. 1996c Nitrogen uptake of Tifgreen bermudagrass in response to golf greens grade polymer-coated ammonium sulfate 171 174 Cisar J.L. Turfgrass research in Florida Univ. Florida, Inst. Food Agr. Sci Gainesville

    • Search Google Scholar
    • Export Citation
  • Wang, F.L. & Alva, A.K. 1996 Leaching of nitrogen from slow-release urea sources in sandy soils Soil Sci. Soc. Amer. J. 60 1454 1458

  • Willis, L.E., Davies, F.S. & Graetz, D.A. 1991 Fertigation and growth of young ‘Hamlin’ orange trees in Florida HortScience 26 106 109

  • Yeager, T.H. & Henley, R.W. 2004 Irrigation and fertilization for minimal environmental impact Acta Hort. 638 233 240

  • Zekri, M. & Koo, R.C.J. 1992 Use of controlled-release fertilizers for young citrus trees Scientia Hort. 49 233 241

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 93 93 11
PDF Downloads 100 100 11