64 Fair et al.: Maple (Acer spp.) Response to Soil Compaction and Pre-plant Nitrogen Arboriculture & Urban Forestry 2012. 38(2): 64–74 Response of Eight Maple Cultivars (Acer spp.) to Soil Compaction and Effects of Two Rates of Pre-plant Nitrogen on Tree Establishment and Aboveground Growth Barbara A. Fair, James D. Metzger, and James Vent Abstract. This study assessed soil compaction effects on aboveground growth of maple cultivars, and compared two nitrogen rates applied pre-planting for their influence on establishment and growth of trees planted into compacted soils. Eight commonly used maple cultivars of Acer rubrum and Acer × freemanii were evaluated. During container production, plants received either 25 or 100 mg·L-1 twice per day. Trees were planted into non-compacted field plots with a mean bulk density of 1.40 g·cm-3 density of 1.60 g·cm-3 nitrogen through fertigation , or into compacted plots with a mean bulk tion of this treatment, mean bulk density was 1.55 g·cm-3 . In 2002, researchers randomly selected half of the compacted plots and applied an additional soil treatment. At the comple- . Trees growing in higher density soils had significantly smaller aboveground biomass measures (P < 0.05), than those growing in non-compacted plots. There was a significant difference between cultivars (P < 0.0001); for example, ‘Celzam’ and ‘Fairview Flame’ had greater aboveground biomass values than other cultivars when grown in compacted soils, but compaction still affected growth. The 100 mg·L-1 nitrogen rate increased leaf dry weight and area, but did not impact height and caliper growth or stem dry weight. Key Words. Acer × freemanii; Acer rubrum; Compaction; Freeman Maple; Nitrogen Rates; Red Maple; Tree Establishment. Construction, foot, and vehicular traffic, recreational activities, and limited mulching may contribute to soil compaction in ur- ban areas (Smiley et al. 1990). Alberty et al. (1984) assessed a variety of urban and suburban sites and found bulk densities ranging from 1.40 to 1.65 g·cm-3 . These compaction levels were shown to limit biomass growth for various species; however, plant responses varied by species, intensity of compaction, soil water content, and soil textural types (Alberty et al. 1984; Pan and Bassuk 1985; Day and Bassuk 1994; Day et al. 2000). Low water and oxygen diffusion rates, reduction in saturated hydrau- lic conductivity, and reduction in infiltration and percolation rate of water characterize highly compacted soils (Boone and Veen 1994). Trees respond to compacted sites by producing shorter, thicker root systems, with more lateral branching (Taylor 1974; Pan and Bassuk 1985; Gilman et al. 1987; Liu and Waldron 1988), which can mean an increase in surface area of root sys- tems per volume at shallow soil depths (Liu and Waldron 1988). Such altered root growth can make plants less drought tolerant and more susceptible to stress overall (Gilman et al. 1987; Wat- son et al. 1996). Additionally, compacted conditions can limit nutrient uptake for either the entire root system or only a portion (Lipiec and Stepniewski 1995). If the entire root system is not affected, the plant can still obtain sufficient levels of nutrients, and a deficiency will not be evident. Typically, the root:shoot ra- tio increases with compaction because height, caliper, and dry weights of plants are reduced with an increase in soil strength or density (Alberty et al. 1984; Masle and Passioura 1987; Cook et ©2012 International Society of Arboriculture al. 1996; Montagu et al. 2001). Other studies found that although there were reductions in root dry weight due to compaction, the reductions were not significant (Andrade et al. 1993). Most often there is a pronounced response in aboveground biomass produc- tion (Taylor 1974; Pan and Bassuk 1985; Pittenger and Stamen 1990; Unger and Kaspar 1994; Day et al. 2000). Many of these physiological responses are similar to those brought on by wa- ter stress (Andrade et al. 1993; Whalley et al. 1995; Liang et al. 1999). Some tree species will adapt to compacted or dry soil con- ditions by developing an adventitious root system in the upper layers of the soil or in the mulch where impedance is reduced, aeration is greater, and water availability is higher (Hook and Brown 1973; Gilman et al. 1987; Liang et al. 1999). Although some species may adapt in this way, other species exposed to such stressors may not be able to recover when conditions abate over time, or recovery may be delayed for many days (Bengough and Young 1993), which can lead to increased plant stress. If re- sponses to compaction and water stress are similar, one possible management strategy for compacted soils, in addition to loos- ening soil, is proper irrigation, especially during establishment. Characterizing urban soils and tree response is difficult due to a wide variety of soil types, site conditions, and tree species planted. The challenge for urban forest managers is to find spe- cies that will grow and thrive in these variable urban sites. An- ecdotally, many urban foresters believed high rates of nitrogen and irrigation during production reduced the establishment suc- cess of trees when planted in difficult urban sites. Some experts
March 2012
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