Evaluation of Liquid-Applied Nitrogen Fertilizers on Kentucky Bluegrass Turf

Solution and suspension N sources have been developed as substitutes Cor urea in spray solutions used by lawn-care proCessionals. A field study was conducted to evaluate the response of Kentucky bluegrass (Poa prarensis L.) growing on a Catlin silt loam (Typic ArgiudoLl), to applications oC the nell' solution and suspension N sources, alone or combined with urea, by comparison to turC response from application of the traditional Certilizer materials ammonium nitrate (AN), NitroCorm (ureaform), sulCur-coated urea (SCU), ammonium sulfate (AS), granular urea, spray-applied urea (US), and urea-ammonium nitrate (UAN) solution. Also, urea and AS treated with dicyandiamide (DCD) were compared to the untreated sources. Fertilization rate was 195 kg N ha I yr I split into Cour applications except seu which was applied twice. TurCgrass color and clipping production were monitored along with thatch accumulation and soil pH. In a second field experiment, Coliar burn potentials oC the new N sources were el'aluated by comparison to burn potentials Crom US, DAN, and a liquid 12-1.8-3.3 Certilizer. TurC response to Formolene (solution N source) paralleled that due to US. TurC treated with US received higher color ratings than did that treated with NitroCorm or FLUF (suspension N source) during the early growing season but this trend was reversed by late summer. Turf fertilized with FLUF resembled turf fertilized with Nitroform but was inferior to turf fertilized with SCU. There was no benefit from the inclusion of DCD with either AS or urea. Soil pH after 2 yr ranged from 5.3 to 6.4 and was lowest with AS treatment; thatch depth ranged from 7.0 to 19.3 mm and was greatest with AS treatment. Formolene and FLUF caused less Coliar injury than did US, UAN, or the 12-1.8-3.3 Certilizer. Results from the two experiments indicated that the major advantage oC using Formolene or FLUF was the reduced potential Cor foliar fertilizer burn. Addirional index words: Turfgrass, Poa prarensis L., Liquid fertilizers. Nitrogen sources, Fertilizer burn, Dicyandiamide. T URF fertilizers can be classified as either quickrelease (water soluble N sources) or slow-release (sources with a dissolution rate much less than that obtained for a completely water soluble source). Quickrelease fertilizers provide a rapid initial turf response but may overstimulate the grass or cause foliar injury and have a short residual (2). Lawn-care professionals make three to five applications of fertilizer to a home lawn during the year. I Contribution from the Horticulture Oep., University of Illinois at Urbana-Champaign. This study was part of project no. 65-0267 ofthe Agric. Exp. Stn., College of Agric., Univ. of Illinois at UrbanaChampaign, Urbana, IL 61801. Received 13 Oec. 1985. ~Former graduate research assistant, Oep. of Horticulture, Univ. of Illinois at Urbana-Champaign, currently extension adviser-horticulturist, McHenry County, Illinois; associate professors, Oep. of Horticulture, Uni v. of Illinois at Urbana-Champaign, IL. Published in Agron. J. 78: 1002-1006 (1986). Because customer satisfaction depends on a noticeable turfgrass response to the applied treatment, the lawncare companies generally use quick-release N sources. Because of its low cost, high water solubility, and relatively low salt index compared to other soluble N sources, urea is the predominant N source used by this industry. Urea is applied either as a spray with water or in a granular form. During certain times of the year. turf response to urea can dissipate before the next application of fertilizer can be made. Also, there is the potential for foliar fertilizer burn because of the wide range of environmental conditions encountered in scheduling multiple applications to a large customer base. Alternative N sources have been developed for use by lawn-care companies that apply fertilizer as a spray solution in attempts to overcome the drawbacks of urea. These include a suspension N source (FLUF; W.A. Cleary Chemical Corp., Somerset, NJ) and a solution N source (Formolene; Hawkeye Chemical Co.• Clinton, IA) with lower salt indexes than urea. Both materials are manufactured by reacting urea and formaldehyde [FLUF, (10); Formolene. (7)], but reaction conditions are such that only a small amount (3.6%) of water insoluble nitrogen (WIN) is contained in FLUF and no WIN is in Formolene. Nitroform (380-0; NOR-AM Chemical Co., Wilmington, DE), the first ureaform fertilizer developed for turfgrass, contains 27% WIN. The response characteristics of Nitroform have been reported previously (1,4,6,11,13,14,15,17,18), but little information has been published regarding turf response to Formolene and FLUF. A strategy to extend the response period of a quickrelease fertilizer is to combine the N source with a nitrification inhibitor. There have been reports on the efficacy of the nitrification inhibitors nitrapyrin [2chloro-6-(tricholromethyl)pyridine] and terrazole (5ethoxy-3-trichloromethyl-l ,2,4-thiadiazole) in crop situations (5), but less is known regarding the response of turfgrass to nitrogen sources treated with nitrification inhibitors. Waddington et al. (16) found no significant advantage from the inclusion ofnitrapyrin with liquid applications ofa 20-13-16.6 soluble N source. Oicyandiamide (OCD) is a nitrification inhibitor that is 66% N and breaks down in the soil to form ammonia and carbon dioxide (12). Landschoot (4) reported little benefit from including DCO with ammonium sulfate