Impact of Fertigation versus Controlled-release Fertilizer Formulations on Nitrate Concentrations in Nursery Drainage Water

in HortTechnology

Nitrate-nitrogen (N) losses in surface drainage and runoff water from ornamental plant production areas can be considerable. In N-limited watersheds, discharge of N from production areas can have negative impacts on nontarget aquatic systems. This study monitored nitrate-N concentrations in production area drainage water originating from a foliage plant production area. Concentrations in drainage water were monitored during the transition from 100% reliance on fertigation using urea and nitrate-based soluble formulations (SF) to a nitrate-based controlled-release formulation (CRF). During the SF use period, nitrate-N concentrations ranged from 0.5 to 322.0 mg·L−1 with a median concentration of 31.2 mg·L−1. Conversely, nitrate-N concentrations during the controlled-release fertilization program ranged from 0 to 147.9 mg·L−1 with a median concentration of 0.9 mg·L−1. This project demonstrates that nitrate-N concentrations in drainage water during the CRF program were reduced by 94% to 97% at the 10th through 95th percentiles relative to the SF fertilization program. Nitrate-N concentrations in drainage water from foliage plant production areas can be reduced by using CRF fertilizer formulations relative to SF formulations/fertigation. Similar results should be expected for other similar containerized crops. Managers located within N-limited watersheds facing N water quality regulations should consider the use of CRF fertilizer formulations as a potential tool (in addition to appropriate application rates and irrigation management) for reducing production impacts on water quality.

Abstract

Nitrate-nitrogen (N) losses in surface drainage and runoff water from ornamental plant production areas can be considerable. In N-limited watersheds, discharge of N from production areas can have negative impacts on nontarget aquatic systems. This study monitored nitrate-N concentrations in production area drainage water originating from a foliage plant production area. Concentrations in drainage water were monitored during the transition from 100% reliance on fertigation using urea and nitrate-based soluble formulations (SF) to a nitrate-based controlled-release formulation (CRF). During the SF use period, nitrate-N concentrations ranged from 0.5 to 322.0 mg·L−1 with a median concentration of 31.2 mg·L−1. Conversely, nitrate-N concentrations during the controlled-release fertilization program ranged from 0 to 147.9 mg·L−1 with a median concentration of 0.9 mg·L−1. This project demonstrates that nitrate-N concentrations in drainage water during the CRF program were reduced by 94% to 97% at the 10th through 95th percentiles relative to the SF fertilization program. Nitrate-N concentrations in drainage water from foliage plant production areas can be reduced by using CRF fertilizer formulations relative to SF formulations/fertigation. Similar results should be expected for other similar containerized crops. Managers located within N-limited watersheds facing N water quality regulations should consider the use of CRF fertilizer formulations as a potential tool (in addition to appropriate application rates and irrigation management) for reducing production impacts on water quality.

Nitrogen applications are essential for producing quality ornamental plants. Nitrogen commonly is applied as nitrate (NO3) or ammonium (NH4+)-N in commercially available soluble and/or controlled-release fertilizer formulations. Ammonium-N is oxidized to nitrite and nitrate by soil-dwelling microorganisms (Goh and Haynes, 1977; Haynes and Goh, 1977; Salisbury and Ross, 1992). Nitrate-N and ammonium-N delivered in SF formulations are readily dissolved in water because of their ionic structures (Handreck and Black, 2002; Wulfsberg, 2000). Consequently, they both have a high potential for moving with water once dissolved. Nitrogen leaching from CRF formulations depends on the dissolution and transport of nutrients through a polymer coating and degradation of an exterior coating or nitrate-embedded polymer. Nitrate leaching from either formulation type from containers is enhanced by the low anion-holding capacity of most media used for plant production (Handreck and Black, 2002). Nitrate present in liquid fertilizer formulations is more likely to enrich drainage water as it is already dissolved (Broschat, 1995; Wilson et al., 2010).

Nitrogen enrichment of nursery runoff and drainage water can have major effects on nursery drainage infrastructure and other nontarget aquatic environments owing to eutrophication. Eutrophication is defined as an increase in the concentration of plant nutrients (deGruyter, 1996). Eutrophication is usually indicated by algal blooms and excessive production of aquatic plants relative to a pre-eutrophic period. Drainage and irrigation recycling infrastructure problems resulting from eutrophication include increased filter clogging (for irrigation systems using recycled surface water) and increased maintenance of drainage ditches and reservoirs owing to excessive production of algae and aquatic plants. Off-nursery discharge of nitrate-N-enriched drainage water, especially into N-limited aquatic ecosystems, may result in loss of desirable aquatic habitats and undesirable changes to natural ecosystems due to eutrophication (Carpenter, 2005; Fisher et al., 2006; Hart et al., 2004; Howarth and Marino, 2006; Livingston, 2007; Mitsch et al., 2001). Nitrogen concentrations greater than 0.4 mg·L−1 have been shown to accelerate eutrophication (Taylor et al., 2006; Vitousek et al., 1997; Wetzel, 1983), cause harmful algal blooms (Rabalais et al., 1996; Taylor et al., 2006), and cause eelgrass (Zostera marina) declines (Burkholder et al., 1992; Taylor et al., 2006).

According to the U.S. Environmental Protection Agency (EPA), nutrients, including nitrate-N, were among the top 10 pollutants preventing lakes, streams, and estuaries from meeting their designated uses in 2004 (EPA, 2009). With increased pressures from state and federal regulatory agencies to reduce nutrient enrichment of lakes, streams, and estuaries, nursery managers need to consider economically viable methods for reducing nutrient enrichment of water drained from production areas into natural water bodies. This research project provides detailed information on the potential contribution of nitrate-N (from SF or CRF) to production area drainage water at the production area scale. While nitrate-N concentration data are available for both formulation types at the container-leaching scale, no data are available documenting the impacts on drainage water quality when making the transition from liquid fertilization to slow-release fertilization programs at the production area scale. This information is particularly important for providing quantitative measurements of the reductions possible within a commercial nursery. The intent of this study was not to exhaustively study all the factors associated with nitrate-N leaching and losses associated with each formulation, but to characterize concentrations in drainage water downstream from the production areas before, during, and after the transition.

Materials and methods

Site description.

This study was conducted at a commercial foliage plant nursery located in Fort Pierce, FL. Two production areas drained into the area from where water samples were collected. One of the production areas was 4 acres in total size, with lady palms (Raphis excelsa) occupying ≈95% of the area and various other species occupying the remaining space. The second production area was 3.5 acres, occupied with ≈80% ficus (Ficus spp.), 10% dragon trees (Dracena spp.), and 10% zz plants (Zamioculcas zamiifolia). Aisles, roadways, and other empty production spaces accounted for less than 20% of the total production area (P. Roldan, personal communication). Both production areas were covered with an automated shadecloth system. Plant/pot sizes within the production area ranged from liners in 32-cell trays to 17-inch pots. The proprietary media composition within the pots varied with plant species, but consisted primarily of Canadian peat, pine bark, and lava rock at varying ratios. Production area ground surfaces were covered with woven landscape fabric underlain by polypropylene plastic, creating a water-impermeable surface that sloped toward concrete roadways. The concrete roadways were sloped to convey drainage water to an underground drainage sump system that was accessible through steel grate-covered concrete structures. The underground system was connected to a perimeter ditch system from which surface water was pumped back into the irrigation reservoir. All plants within the nursery were irrigated using one or more button pot drippers per pot (2 or 4 L·h−1 flow rate; Netafin, Tel Aviv, Israel) depending on the plant size and species.

Fertilization scenarios.

Fertilization scenarios were selected by the nursery managers on the basis of costs. Historically, all plant fertility requirements were met using fertigation at the nursery. During the monitored fertigation periods, plants received a 7N–1.3P–5.8K urea-based formulation (Douglas Fertilizer, Hastings, FL) on days 1 to 53 (1 Feb. to 30 May 2008) or a 6N–1.3P–7.5K or 7N–0.9P–5.8K nitrate-based fertigation formulation (Helena Chemical, Collierville, TN) on days 54 to 112 (3 June to 4 Nov. 2008). Irrigation and fertigation rates varied depending on the delivered fertilizer concentration, plant needs, and standard production protocols at the nursery, including maintenance of target electrical conductivity levels of 2 dS·m−1 and a leaching volume of ≈20%. On about day 112 of this study, the fertilization for the entire nursery was changed to a 20N–1.7P–9.9K controlled-release, nitrate-based formulation (Leonard's Ornamental Mixes, Port St. Lucie, FL) to save on production costs. This fertilizer was applied at a rate of ≈15 g/gal pot size. Irrigation management remained the same according to plant needs and standard practice throughout the remainder of the study (4 Nov. to 6 Dec. 2008).

Sample collection and analysis.

For the results reported, water samples were collected over a 191-d period bracketing the transition period for the fertilization changes. Water from the sump was pumped continuously (575 L·h−1) into duplicate 242-L polyethylene tanks by using a large waterfall and stream pump (W1150; Beckett, Norfolk, VA) suspended in a floating, net-covered polyvinyl chloride cage that provided prefiltering of large plant and organic materials. The polyethylene tanks were equipped with free-flowing outlets as part of another research project. Duplicate composite samples were collected from the polyethylene tanks using two ice-cooled American Sigma autosamplers (Hach, Loveland, CO) at 15-min intervals during each 16- to 24-h sampling period. Samples were immediately placed on ice after collection and transported to the laboratory where they were analyzed for nitrate using an ion chromatograph (ICS-1000; Dionex, Sunnyvale, CA) equipped with an autosampler (AS-40; Dionex) and EPA Method 300.0 (EPA, 1993). Quality control elements included the use of instrument and method blanks and control standards with acceptability limits of ±10%. The method detection limit for nitrate-N was 0.01 mg·L−1.

Summary statistics were computed to describe the nitrate-N concentrations during each monitoring period. These statistics included mean, se, minimum, maximum, and median values. In addition, the 10th, 25th, 50th, 75th, 90th, and 95th percentile rank concentrations were calculated for each period. Percentile ranks are useful for describing the occurrence of values below or above a given target level (e.g., if the 90th percentile concentration is 10 mg·L−1, then 90% of the values were equal to or less than 10 mg·L−1 and 10% were equal to or greater than 10 mg·L−1). These values were computed for each monitoring period (SF vs. CRF) using duplicate measures for each day the samples were collected. The SF period spanned from day 1 through day 112, yielding a total of 224 nitrate-N concentrations. The CRF monitoring portion of the study spanned from day 113 through day 190, yielding a total of 154 nitrate-N concentrations.

Results and discussion

Summaries of the nitrate-N concentrations during the SF and CRF fertilization periods are shown in Table 1 and Fig. 1. During the SF use period (days 1–112), nitrate-N concentrations in the runoff water ranged from 0.5 to 322.0 mg·L−1, with mean and median concentrations of 43.1 and 31.2 mg·L−1, respectively (Table 1). These concentrations were very similar to those reported by Wilson et al. (2010) (0.7–386 mg·L−1) in a similar production area and scenario using only SF. Conversely, nitrate-N concentrations after changing to the controlled-release fertilization program (days 113–179) ranged from 0 to 147.9 mg·L−1, with mean and median concentrations of 4.4 and 0.9 mg·L−1, respectively (Table 1). The highest concentration occurred close to the transition date, probably representing residual from the SF period (Fig. 1). Nitrate-N concentrations in drainage water during the CRF program were reduced by 94% to 97% at the 10th through 95th percentiles relative to the SF fertilization program (Table 1).

Fig. 1.
Fig. 1.

Mean nitrate-nitrogen (N) concentrations (n = two composite samples for each day, each consisting of 64 to 96 subsamples collected at 15-min intervals during each 16- to 24-h sampling period) in drainage water from a 7.5-acre (3.04 ha) foliage plant production area. Plants were fertigated with a 7N–1.3P–5.8K urea-based soluble fertilizer (SF) formulation on days 1 to 53 and a 6N–1.3P–7.5K or 7N–0.9P–5.8K nitrate-based fertigation SF on days 54 to 112. A controlled-release fertilizer formulation (20N–1.7P–9.9K) was used during days 113 to 190; 1 mg·L−1 = 1 ppm.

Citation: HortTechnology hortte 21, 2; 10.21273/HORTTECH.21.2.176

Table 1.

Summary of nitrate-nitrogen (N) concentrations in drainage water from a 7.5-acre (3.04 ha) foliage plant production area during fertigation [soluble formulation (SF)] and controlled-release fertilizer (CRF) use periods. Concentrations are based on analysis of daily composite samples (n = 2), each consisting of 64 to 96 subsamples collected at 15-min intervals during each 16- to 24-h sampling period. Plants were fertigated with a 7N–1.3P–5.8K urea-based formulation and a 6N–1.3P–7.5K or 7N–0.9P–5.8K nitrate-based fertigation formulation during the SF monitoring period. During the CRF monitoring period, a 20N–1.7P–9.9K formulation was used.

Table 1.

These results indicate that the use of a CRF formulation can be very successful in reducing nitrate enrichment of drainage water (relative to SF) originating from foliage plant production nurseries. Using the EPA drinking water standard (44.3 mg·L−1 nitrate or 10 mg·L−1 nitrate-N) as a reference point, 85% of the samples collected during the fertigated period had nitrate concentrations greater than 10 mg·L−1 N (EPA, 2010). In contrast, only 4% of the samples collected following the transition to the controlled-release formulation exceeded 10 mg·L−1. Those concentrations that exceeded the threshold during the CRF monitoring phase were likely associated with residuals from the SF program.

While these results endorse CRF use for reducing nitrate-N discharges from production areas, use of CRFs does not ensure that nitrate levels in drainage water will be reduced in all situations. Cox (1993) reported some situations where nitrate leaching from CRFs may exceed leaching losses from SF formulations. Evaluating nitrate leaching from marigold (Tagetes erecta), Cox (1993) reported that single CRF applications of the total crop N at planting resulted in more nitrate leaching by the end of the crop cycle relative to SF applications. These losses likely resulted in the provision of more nitrate earlier on than the crop could effectively take up and use. Cox (1993) also reported considerable reductions in nitrate leaching (relative to SF or a single N application) when the total N application was split during the crop cycle. One major difference between this study and that of Cox (1993) is the size of the plants. Plants in the Cox (1993) study started off as marigold seedlings that were grown to marketable size within a 60-d production cycle. The foliage plants within this study were well-established nonseedlings under a much longer production cycle. Plants are normally kept in this area until they are sold, with transplantation to larger pots as the production period increases. Typical production times range from 10 to 24 months depending on markets. The higher-density foliage plant root systems were more likely to intercept nutrients as they were released from the CRFs. The potentially large leaching losses from CRFs in the absence of sufficient roots is further supported by Merhaut et al. (2006) and Newman et al. (2006), who evaluated release characteristics of four types of CRF formulations over a 47-week simulated production cycle under greenhouse and outdoor conditions. Merhaut et al. (2006) reported nitrate-N concentrations in leachates under unheated greenhouse conditions ranging from <10 mg·L−1 during the first 4 weeks of the study to >100 mg·L−1 from weeks 4 to 9 and ≈30 mg·L−1 from week 10 to 47 of the study. Under outdoor conditions, nitrate-N concentrations were <25 mg·L−1 during the first 4 weeks, increasing to >250 mg·L−1 and then fluctuating between 100 and 200 mg·L−1 until week 20, after which the concentrations were not <100 mg·L−1 through week 40 and <50 mg·L−1 during the final 7 weeks. These studies represented a worst-case scenario for nutrient release as plants were not included in the experimental units (Merhaut et al., 2006; Newman et al., 2006). Addition of actively growing plants would certainly reduce the leaching losses observed.

On a nursery production area scale, the results also agree with those of Colangelo and Brand (2001), who reported average annual flow-weighted nitrate concentrations in leachates from controlled-release-fertilized, containerized rhododendron (Rhododendron catawbiense ‘Album’) crops of 7.2 mg·L−1 (1.6 mg·L−1 N) for overhead irrigation and 12.7 mg·L−1 (2.9 mg·L−1 N) for trickle irrigation. Those concentrations fell within the 75th and 90th percentiles for the CRF portion of this study, indicating some similarities and repeatability between different production systems. Likewise, Yeager et al. (1993) evaluated nitrate concentrations in runoff and collection pond water at six nurseries within the southeastern United States. They reported average nitrate-N concentrations of 8 mg·L−1 (range = 0.5 to 33 mg·L−1) in production bed runoff for nurseries using only CRFs, which was within the 96th percentile concentration detected in the CRF portion of this study. Warsaw et al. (2009) reported nitrate-N concentrations of ≤5.5 mg·L−1 in runoff water from nursery plots fertilized with CRF and irrigated under four different scenarios over 2 years. The average nitrate-N concentration during the CRF application period in the current study was 4.4 mg·L−1 (range = 0 to 147.9 mg·L−1). Conversely, average nitrate-N concentrations at nurseries using CRF with supplemental SFs were 20 mg·L−1 (range = 0.1 to 135 mg·L−1) in the Yeager et al. (1993) study, which is lower than the 43 mg·L−1 (range = 0.5 to 322 mg·L−1) in the SF-only portion of this study. Taylor et al. (2006) also reported that nitrate-N concentrations in nursery runoff water from a nursery using CRF supplemented with SFs ranged from 11.1 to 29.9 mg·L−1 during the spring fertilization period and from 2.8 to 5.2 mg·L−1 during the plant dormancy period in the winter.

While phosphorus was not monitored during this study, similar but slower release results could be expected. Broschat (1995, 2005) and Huett and Gogel (2000) reported slower losses of phosphorus relative to nitrate-N in controlled-release formulations. Phosphorus losses were also lower relative to soluble formulations in those studies. In addition to reducing nitrate discharges from the production area, fertilizer costs were also reduced by more than 60% (P. Roldan, personal communication). The primary savings were associated with freight charges and more efficient fertilization. During the fertigation period, frequent deliveries of fertilizer solutions in 3000-gal quantities were necessary (use requirements were ≈1000 gal/week for the entire nursery). These deliveries were more expensive, relative to CRF, because of the extra weight of water and the requirement for specialized delivery systems (tankers, tanks, and pumps). Inefficiencies with the fertigation were associated with the need to flush the main lines before and after each fertigation event to prevent clogging. These flushing events washed the fertigation solutions directly through the lines and into the drainage system without any potential benefit to plant production. Nursery production managers using fertigation and production areas that are located within N-limited watersheds with state or federal mandated N regulations should consider the use of controlled-release fertilizer formulations for reducing N enrichment of drainage water, especially if they discharge into off-site water systems.

Although this study was conducted at a foliage plant nursery, similar results might be expected for the production of other horticultural commodities. However, site-specific conditions may be critical in determining the suitability and useable lifespan of controlled-release formulations. Nitrate-N release rates are strongly influenced by temperature and substrate moisture content (Broschat, 2005), while nutrient leaching potential from pots fertilized with controlled-release formulations may be affected by the initial loading placed into each pot and the presence of sufficient roots to absorb the nutrients as they are released (Cox, 1993; Merhaut et al., 2006; Newman et al., 2006). Proper irrigation management is also critical to obtain the maximal benefits of nutrient leaching reduction (Warsaw et al., 2009). Regardless of formulation, fertilizers are more susceptible to leaching losses when plants are very young and roots have not developed enough to absorb substantial amounts. Under these conditions, careful irrigation and fertility management is a necessity to reduce leaching losses.

Conclusions

Results indicate that nitrate-N concentrations in drainage water from foliage plant production areas can be substantially reduced by using CRF formulations relative to SF formulations/fertigation. Similar results should be expected for other similar, containerized crops. Managers located within N-limited watersheds facing N water quality regulations should consider the use of the CRF fertilizer formulations as a potential tool (in addition to appropriate application rates and irrigation management) for reducing production impacts on water quality.

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Literature cited

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Contributor Notes

We thank Kevin Kraft, Pedro Roldan, Jeff Shultz, and Alex Fell for access to their nursery and expertise. We also gratefully acknowledge financial support of this project from the USDA-ARS Floriculture and Nursery Research Initiative; project number 6618-13000-003-05S “Water Quality Protection Using Bioremediation and Decision Support Technologies.” We also thank Ryan Hamm, University of Florida/IFAS, and Chris Lasser, USDA, for their technical assistance with this project.

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

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    Mean nitrate-nitrogen (N) concentrations (n = two composite samples for each day, each consisting of 64 to 96 subsamples collected at 15-min intervals during each 16- to 24-h sampling period) in drainage water from a 7.5-acre (3.04 ha) foliage plant production area. Plants were fertigated with a 7N–1.3P–5.8K urea-based soluble fertilizer (SF) formulation on days 1 to 53 and a 6N–1.3P–7.5K or 7N–0.9P–5.8K nitrate-based fertigation SF on days 54 to 112. A controlled-release fertilizer formulation (20N–1.7P–9.9K) was used during days 113 to 190; 1 mg·L−1 = 1 ppm.

  • BroschatT.K.1995Nitrate, phosphate, and potassium leaching from container-grown plants fertilized by several methodsHortScience307477

  • BroschatT.K.2005Rates of ammonium-nitrogen, nitrate-nitrogen, phosphorus, and potassium from two controlled-release fertilizers under different substrate environmentsHortTechnology15332335

    • Search Google Scholar
    • Export Citation
  • BurkholderJ.MasonK.M.GlasgowH.B.Jr.1992Water-column nitrate enrichment promotes decline of eelgrass Zostera marina: Evidence from seasonal mesocosm experimentsMar. Ecol. Prog. Ser.81163178

    • Search Google Scholar
    • Export Citation
  • CarpenterS.R.2005Europhication of aquatic ecosystems: Bistability and soil phosphorusProc. Natl. Acad. Sci. USA1021000210005

  • ColangeloD.J.BrandM.H.2001Nitrate leaching beneath a containerized nursery crop receiving trickle or overhead irrigationJ. Environ. Qual.3015641574

    • Search Google Scholar
    • Export Citation
  • CoxD.A.1993Reducing nitrogen leaching-losses from containerized plants: The effectiveness of controlled-release fertilizersJ. Plant Nutr.16533545

    • Search Google Scholar
    • Export Citation
  • deGruyterW.1996Concise encyclopedia biologyWalter deGruyterNew York

    • Export Citation
  • FisherT.R.HagyJ.D.IIIBoyntonW.R.WilliamsM.R.2006Cultural eutrophication in the Choptank and Patuxent estuaries of Chesapeake BayLimnol. Oceanogr.5435447

    • Search Google Scholar
    • Export Citation
  • GohK.M.HaynesR.J.1977Evaluation of potting media for commercial nursery production of container grown plants. 3. Effects of media, fertilizer nitrogen, and a nitrification inhibitor on soil nitrification and nitrogen recovery of Callistephus chinensis (L.) Nees ‘Pink Princes’N.Z. J. Agr. Res.20383393

    • Search Google Scholar
    • Export Citation
  • HandreckK.BlackN.2002Growing media for ornamental plants and turf3rd edUniv. New South Wales PressSydney, Australia

    • Export Citation
  • HartM.R.BertF.Q.Long NguyenM.2004Phosphorus runoff form and agricultural land and direct fertilizer effects: A reviewJ. Environ. Qual.3319541972

    • Search Google Scholar
    • Export Citation
  • HaynesR.J.GohK.M.1977Evaluation of potting media for commercial nursery production of container-grown plants. II. Effects of media, fertiliser nitrogen, and a nitrification inhibitor on yield and nitrogen uptake of Callistephus chinensis (L.) Nees ‘Pink Princes’N.Z. J. Agr. Res.20371381

    • Search Google Scholar
    • Export Citation
  • HowarthR.W.MarinoR.2006Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decadesLimnol. Oceanogr.51364376

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