Nutrient Release from Controlled-release Fertilizers in a Neutral-pH Substrate in an Outdoor Environment: II. Leachate Calcium, Magnesium, Iron, Manganese, Zinc, Copper, and Molybdenum Concentrations

Nutrient release characteristics of four different controlled-release fertilizers (Osmocote, Nutricote, Polyon, and Multicote) were monitored during an 11-month period in a simulated outdoor nursery production facility. Although no plants were used in the experiment, fertilization rates, irrigation regimes, and cultural practices simulated those typically used to produce fast-growing, high-nutrient-requiring containerized woody ornamentals. Fertilizer prill release characteristics were monitored through analyses of leachates, which were collected weekly. Concentrations of Mg, Mn, Zn, Cu, and Mo were relatively high during the first 5 to 10 weeks of the experiment, then declined and usually stabilized during the remainder of the study. However, Mn and Zn displayed erratic increases in concentrations several times throughout the study. Calcium concentrations did not increase until the fifth week, rapidly peaked to about 300 mg L, and then decreased and leveled off to 80 to 100 mg L during the remainder of the study. Several significant differences were observed between treatments. The Osmocote treatment had significantly greater Ca and Mg concentrations in the leachate than the other fertilizer types during the last 6 weeks of the study, whereas the Nutricote treatment often had significantly greater Fe concentrations than leachates from other treatments, especially during the last 26 to 35 weeks of the study, and significantly greater Zn concentrations than the other CRFs during the last 21 weeks of the study. Based upon U.S. Environmental Protection Agency guidelines, concentrations of Fe were often more than the allowable limit of 0.3 mg L with all fertilizer types, but especially with Nutricote. Concentrations of Mn and Cu also exceeded federal guidelines, particularly during the first several weeks of the study. As previously discussed in the literature (Blythe, et al., 2006; Merhaut, et al., 2006), plant nutrients, other than nitrate (NO3 ) and P, are listed under the Clean Water Act (U.S. Environmental Protection Agency, 1994) as potential pollutants of impaired water bodies. Some state agencies, such as the Regional Water Quality Control Board for Los Angeles, have already listed Mn, Cu, and Zn as potential pollutants that need to be monitored (Harris and Dasker, 1994). However, aside from monitoring N, P, and K, few studies have been conducted to determine the fate of other essential plant nutrients derived from polymer-coated controlled-release fertilizers (CRFs) when used in a typical nursery production scenario. In earlier studies (Blythe et al., 2006; Merhaut et al., 2006), release and leaching characteristics of plant essential nutrients from CRFs were determined in a greenhouse production system using the cultural practices of low N fertilizer (1.17 kg m) rates and an acid pH, peat/pine bark/sand substrate. In the current study, the nutrient release characteristics of the same CRFs were studied using cultural practices (relatively high fertilizer rates, neutral pH, composted forest products/pine bark/sand substrate, and an outdoor climate) commonly used for suntolerant, fast-growing woody ornamentals. With this information, we hope to determine the patterns of release and leaching of plant essential nutrients from the CRFs and substrate so that CRF formulations or fertilizer and substrate management practices typically used for outdoor production practices can be manipulated to optimize nutrient uptake efficiency and simultaneously reduce the likelihood of nutrient runoff from nursery production facilities. Materials and Methods Experimental procedures are described by Newman et al. (2006). However, an abbreviated description follows, emphasizing the protocols associated with the use and measurement of Ca, Mg, Fe, Mn, Cu, Zn, andMo. Substrate. Substrate consisted of a 5:3:1 mixture of composted forest products (ScottSierra Horticultural Products Co., Marysville, Ohio), pine bark (6.4–9.5 mm), and washed builder’s sand (by volume). The substrate was amended with dolomite 65 (Chemical Lime Co., Scottsdale, Ariz.) at a rate of 1.78 kg m and ultrafine calcium sulfate (Western Mining and Minerals, Apex, Nev.) at a rate of 0.59 kg m. This provided 0.50 gMg/no. 1 container and 0.97 g Ca/no. 1 container from dolomite and 0.42 g Ca/no. 1 container from the calcium sulfate. Random samples of air-dried substrate was ground to 0.420 mm and extracted in water for nutrient analyses. Calcium, Mg, Fe, Mn, Zn, Cu, and Mo in extracts were quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES; model IRIS 1000 HR; Thermo Electron Corp., Franklin, Mass.). Nutrient concentrations of substrate before the addition of CRFs were 25.98 mg L Ca, 9.27 mg L Mg, 7.16 mg L Fe, 1.78 mg LMn, 5.14 mg L Zn, 0.20mg L Cu, and 0.01 mg L Mo. Fertilizer treatments. Treatments consisted of four different 365-d-release CRFs: Multicote 17–5–11 + minors (Haifa Chemicals, Ltd., Haifa Bay, Israel), Nutricote 18– 6–8 total (Chisso-Asahi Fertilizer Co., Tokyo), Osmocote 24–4–9 (Scott-Sierra Horticultural Products Co.), and Polyon 17–5–11 + micros (Pursell Technologies, Sylacauga, Ala.). All CRFs are polymer—coated formulations that Received for publication 2 June 2006. Accepted for publication 9 July 2006. This research was funded in part by grants from the Hansen Trust Fund and the California Department of Food and Agriculture Fertilizer and Research and Education Program (CDFA-FREP). Trade names are mentioned throughout this manuscript, but this does not imply product endorsement by the authors and their associated institutions. Special thanks are given to ShahramAhmadian and Harold D. Ewing for their technical assistance. To whom reprint requests should be addressed; e-mail [email protected]. HORTSCIENCE VOL. 41(7) DECEMBER 2006 1683 JOBNAME: horts 41#7 2006 PAGE: 1 OUTPUT: October 28 13:29:46 2006 tsp/horts/127877/01665