Arboriculture & Urban Forestry 35(5): September 2009 (Smith 1978; Neely 1980), and season of application (Struve and Rose 1998; Rose 1999). Therefore, the objectives of this research were to quantify fertilizer recovery in aboveground tissues, de- scribe fertilizer N partitioning patterns, and evaluate the effect of fertilization on the aboveground N status in common hackberry (Celtis occidentalis L.) using a 15 N enriched fertilizer at the upper and lower rate limits for landscape trees as proposed in the ANSI A-300 (2004) standards. Recovery rates were calculated several times over the course of a single growing season and native soil was used as the rooting media to better simulate landscape soils. METHODS AND MATERIALS Common hackberry, a tree native to eastern and central U.S. and Canada, was used to evaluate fertilizer partitioning and recovery in aboveground biomass at Arlington, Wisconsin and Lisle, Illinois, U.S. This riparian species reaches a height of 15–21 m (50–70 ft) at maturity, is tolerant of a wide range of soil types, pH, mois- ture regimes, and air pollution. As a result, common hackberry is used extensively as a street, park, and landscape tree (Dirr 1998). The Lisle, IL site is located on the grounds of The Morton Arboretum (41°N–88°W) in northeastern Illinois. Mean grow- ing season temperatures (April–September) range from 10–24°C (50–75°F) and the area averages 929 mm (36.6 in) of precipita- tion per year (Illinois State Water Survey 2002). The study site was located in a cleared field formerly consisting of mixed hard- woods. Soils in the study site are Oxyaquic Hapludalfs, domi- nated by Ozaukee silt loam (32% sand, 19% clay, 49% silt), a moderately well-drained soil consisting of a thin silt cap over sand, gravel, silt and clay glacial till (USDA 2000). Average pH, percent soil organic matter (% SOM), and cation exchange capac- ity (CEC) for the Lisle, IL study site were 6.9, 3.8% and 13 cmolc kg-1 The Arlington Horticulture Research Station, Arlington, WI (43°N–89°W) study site is located in south-central Wisconsin. Mean growing season temperatures range from 14–21° C (57–70°F) and the area averages 833 mm (32.8 in) of precipitation per year (Wisconsin State Climatology Office 2002). The study site was formerly used for the production of agricultural crops. Soil in the study site is a Plano silt loam (Typic Argiudoll, 21% sand, 16% clay, 63% silt) that is moderately well-drained to well-drained, and possesses a silt cap approximately 102–152 cm (40–60 in) thick over a sand and gravel glacial till (USDA 1978). Average pH, % SOM, and CEC were 6.2, 3.0%, and 13 cmolc kg-1 soil, respective- ly. Additionally, concentrations of phosphorus (P), calcium (Ca), potassium (K), and magnesium (Mg), within the soil at Arlington, WI were 48.4, 1770, 164, and 436 mg L-1 (ppm), respectively. A randomized complete block design consisting of five blocks, three fertilizer treatment levels and four harvest periods was em- ployed at each study location. On May 10 and May 16, 2002, sixty, 2.54 cm (1 in) caliper, container-grown, grafted trees from Bailey Nurseries, St. Paul, MN, were transplanted into 61 cm (24 in) diameter Root-Control™ bags (Root Control Inc., Oklahoma City, OK) and backfilled with native soil at Lisle, IL and Arling- ton, WI, respectively. Blocks were aligned in an east-to-west di- rection. Spacing between blocks and between trees within a block was 3.05 m (10 ft). Within each of the five blocks, there was one tree per treatment level and harvest period combination (twelve (Ca), potassium (K), and magnesium (Mg), within the soil at Lisle, IL were 20, 1753, 159, and 458 mg L-1 soil, respectively. Concentrations of phosphorus (P), calcium (ppm), respectively. 253 trees per block). Treatments consisted of de-ionized water (0 g N), 1.42 g N (0.05 oz), and 4.27 g N (0.15 oz) per tree dissolved in 7.6 L (2 gal) of de-ionized water and four harvest periods (14, 30, 60 and 90 days after treatment). Fertilizer treatments were the area equivalent of 0, 0.49 and 1.47 kg N 100 m-2 3 lb N 1000 ft-2), respectively. Ammonium-nitrate (NH4 double enriched with the 15N isotope (1.5 atom % for both the NH4 and NO3 + -) was applied at the aforementioned rates on June 12 and June 20, 2002 at Arlington, WI, and Lisle, IL, respec- tively. Root zones were hand-weeded to eliminate competition for fertilizer N throughout the study and supplemental irrigation was provided, as needed, to ensure 2.54 cm of water per week. A composite of five, 2.54 cm by 25.4 cm (10 in) soil cores obtained from the east and west end of each block at the time of transplanting were analyzed at the University of Wisconsin- Madison Soil and Plant Analysis Laboratory (Verona, WI) to determine soil pH (1:1 water), soil organic matter (% loss on ignition), P (Bray P1), K, Ca and Mg (1.0 N ammonium ac- etate), and CEC by summation of extracted K, Ca, and Mg. Foliage (F), current season stem wood (Sc) consisting of the new terminal stem growth, stem wood (S), and roots (R) samples were collected at the time of transplanting to establish baseline total nitrogen and 15 N atom % values. At each harvest period, the entire aboveground biomass was separated into foliage, current season stem wood, and stem wood. Stem samples used in analysis con- sisted of all stem tissue above the graft union. Total root biomass was not determined due to an inability to consistently separate the roots from the container growing medium. Root samples used in analysis consisted of approximately 30–50 g (1.05–1.76 oz) of woody and nonwoody roots obtained equally from the lower, middle, and upper portions of the root system. Root samples were rinsed twice for approximately 5 s per rinse with de-ionized water. Tissue samples were dried at 60°C (140°F) until process- ing. Total dry weight of aboveground tissues used in calculat- ing fertilizer recovery was determined just prior to grinding in a Wiley mill (Thomas-Wiley Laboratory Mills, Philadelphia, PA) to pass a 1 mm (0.04 in) sieve. A homogenized 1 g (0.035 oz) subsample was pulverized in a Crescent “Wig-L-Bug” Dental Amalgamator (Crescent Dental Manufacturing, Chi- cago, IL) for 120 s using two, 5 mm (0.197 in) stainless steel ball bearings, at 5,000 rpm. Approximately 5 mg (0.0002 oz) of pulverized tissue were combusted at 1020°C (1868°F) in a Carlo-Erba Carbon : Nitrogen analyzer (Carlo Erba, Milan, Italy) interfaced with a Europa Scientific TracerMass mass spectrometer (Crew, Cheshire, United Kingdom). Analysis con- sisted of total N and atom % 15 N on a percent dry weight basis. Quality control was verified by duplicate analysis every 10–12 samples. The percentage of fertilizer N recovered was calcu- lated according to methods reported by Kraimer et al. (2001). [Equation 1] N Recovery = ∑ − ( ( N % in fertilized tissue sample N % in tissue prior to fertilization N % in fertilizer F C D ) Where: N = Weight of N(g) in a component tissue A = 15 B = 15 C = 15 D = Natural abundance of 15N which is 0.366% (International ©2009 International Society of Arboriculture N A B − ) (0, 1 and NO3 )
September 2009
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