252 Werner and Jull: Fertilizer Uptake, Partitioning, and Recovery in Container-Grown Trees Arboriculture & Urban Forestry 2009. 35(5): 252–262 Fertilizer Uptake, Partitioning, and Recovery in Container- Grown Common Hackberry (Celtis occidentalis) Trees L.P. Werner and L.G. Jull ing, and aboveground N status in container-grown common hackberry (Celtis occidentalis L.) trees back-filled with native soil at Arlington, Wiscon- sin and Lisle, Illinois, U.S. Treatments consisted of 0, 1.42 g N tree-1 1.47 kg N 100 m-2 Abstract. Ammonium-nitrate (NH4 NO3 (0, 1, and 3 lb N 1000 ft-2 ground N status were significant only at the 4.27 g N tree-1 ) double enriched with the 15 N isotope (1.5 atom %) was used to evaluate fertilizer N recovery, N partition- (0.05 oz) and 4.27 g N tree-1 (0.15 oz), the area equivalent of 0, 0.49, and ). Trees were harvested 14, 30, 60, and 90 days after fertilization. Fertilizer-induced changes in above- (0.15 oz) treatment level. The amount of fertilizer N recovered in aboveground tissues increased with rate of application. Fertilizer N was preferentially partitioned to foliage and current season stem wood. The percentage of fertilizer recovered in aboveground tissues did not differ between the application rates, ranging from 15%–25% at Arlington, WI, and 5%–9% at Lisle, IL. Frost damage to the foliage at Lisle, IL may have resulted in location differences in aboveground biomass which affected fertilizer N uptake and recovery. These data suggest fertilizer N accumulated in nontarget sinks and/or were lost from the site of application at both rates of application. Key Words. ANSI A-300; Fertilization; Landscape Trees; 15 N. Applying nitrogen (N) based fertilizer to landscape trees has been a common arboricultural practice since the early 1900s. Early re- search demonstrated N limitations in urban landscapes with in- creased tree growth following the addition of N fertilizers (Wyman 1936; Neely et al. 1965; Smith 1978; Neely 1980). These growth- based studies and the resulting nutrient management recommen- dations were later supported by reports of reduced rates of N mineralization in urban soils resulting from declines in microbial activity (White and McDonnell 1988), reduced organic N inputs associated with tree litter collection and removal (Werner 2000), and the accumulation of heavy metals (Kandeler et al. 1996). Observed reductions in fertilizer use efficiency (g N/g bio- mass) associated with step-wise increases in plant available N have indicated there is a physiological upper limit to the rate of application (Struve 1995; Rose 1999; Rose and Biernacka 1999). These findings suggest there is an increased potential for off-site losses or the partitioning of fertilizer N into non- target sinks when rates of application exceed a plant’s physi- ological need. In the late 1990s, landscape tree fertilization became a contentious environmental issue as annual N ap- plication rates consistent with tree growth studies were identi- fied as potential nonpoint sources of surface and groundwa- ter contamination (Perry and Hickman 1998; Miller 2003). Nitrate (NO3 -) has been reported to accumulate below the effec- saturated flow, with N losses proportional to the amount of surplus N (Masarik 2003). Similar increases in soil solution NO3 tive rooting depth in agricultural fields when fertilizer applications exceeded total demand for N within the area of application. The accumulated NO3 - was susceptible to leaching during periods of -N have been observed under landscape trees and turfgrass receiving chron- ic fertilizer N additions, suggesting N inputs exceeded the site’s ©2009 International Society of Arboriculture physiological need and/or the ability to retain N and were suscep- tible to leaching (Werner 2000). The environmental ramifications associated with accumulations of fertilizer N in nontarget pools are serious, especially when application rates in excess of physi- ological need are applied on an annual basis (Perakis et al. 2005). Concerns over ground and surface water contamination result- ing from N fertilization of nursery trees (Colangelo and Brand 2001), fruit and citrus trees (Martinez et al. 2002; Scholberg et al. 2002), and turfgrass (Gross et al. 1990) resulted in the increased use of 15 N as an isotopic tag to quantify fertilizer N recovery and define partitioning patterns. For example, whole-plant uptake ef- ficiency (total N uptake/amount of N applied) in production ap- ple trees (Malus sylvestris var. domestica Borkh.) was calculated to be 22% of the recommended application rate (Neilsen et al. 2001). These findings prompted changes in water management practices so as to increase the soil residency time of the fertilizer during periods of peak N demand. Similarly, a mass balance ap- proach was used to quantify recovery from a single application, 49 kg ha-1 (43 lbs N acre-1 ), of 15 N enriched ammonium sulfate in Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) (Engelsjord et al. 2004). Maximum fertilizer N recovery rates of 79% and 91% were observed two days after application for perennial ryegrass and Kentucky bluegrass, re- spectively. One year after treatment, fertilizer recovery rates from the soil and aboveground tissues were approximately 70%. The high recovery rates support claims that a judicious application of fertilizer N, 49 kg ha-1 (43 lbs N acre-1 ), is not prone to leaching. Comparatively, the majority of landscape tree fertilization re- search has focused on stimulating aboveground growth through experimentation with fertilizer formulation and method of deliv- ery (van de Werken 1981; van de Werken 1984), rate of application
September 2009
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