70 Fair et al.: Maple (Acer spp.) Response to Soil Compaction and Pre-plant Nitrogen Table 5. Mean stem dry weight for four cultivars of Freeman and red maple trees harvested in 2004; values shown for soil treatments and pre-plant nitrogen rates. Cultivarz ‘Celzam’ ‘Morgan’ ‘Fairview Flame’ ‘Frank’s Red’ Stem dry weight (g) Soil treatmenty NC 5625 a (a) 5150 a (a) 3068 b (a) 2108 b (a) Stem dry weight (g) Pre-plant N ratex H ‘Celzam’ ‘Morgan’ Figure 2. Mean annual caliper growth (cm·yr-1 ) of eight cultivars of Freeman and red maple trees growing in non-compacted and compacted soil treatments measured in 2002 and 2004. NC = non- compacted, C = mean of plots compacted once and twice (C2); Acer × freemanii ‘Celzam’ (Celebration Freeman maple), Acer × freemanii ‘Morgan’ (‘Morgan’ × Freeman maple), Acer × freemanii ‘October Brilliance’ (‘October Brilliance’ Freeman maple), Acer rubrum ‘Bowhall’ (‘Bowhall’ red maple), Acer rubrum ‘Fairview Flame’ (Fairview Flame red maple), Acer rubrum, ‘Frank’s Red’ (Red Sunset red maple), Acer rubrum ‘Magnificent Magenta’ (Bur- gundy Belle red maple), and Acer rubrum ‘October Glory’ (Octo- ber Glory red maple). Only the red maple cultivar ‘Bowhall’ was unaffected by soil or pre-plant N treatments. The ‘Bowhall’ trees were on aver- age much smaller than all other cultivars over all the biomass measures (Table 3; Table 4). One possible explanation for this anomaly is that ‘Bowhall’ is not suited to clay-based soil types, regardless of whether they are compacted. ‘Celzam,’ a Freeman maple, on average had larger mean biomass measures when compared to all other cultivars, irrespective of soil treatment (Table 3; Table 4); although ‘Celzam’ trees grown in compacted plots had smaller mean biomass measures than trees growing in NC plots (Table 3). In addition, ‘Celzam’ had larger SDW val- ues than both red maples despite the pre-plant N rate (Table 5). DISCUSSION The Effect of Compaction Treatments on Soil Physical Characteristics. soils compacted initially, however not significantly. This could be because rocks or other natural differences across the field may have led to less-than-homogenous compaction (Maurya and Lal 1979). Based on the Proctor results, the volumetric wa- ter content at the time of the second compaction treatment (0.14 g·g-1 The additional compaction treatment in 2002 did not increase the ρb as hoped, and on average was actually lower than the ρb ) was insufficient to raise the bulk density substantially. The Proctor test was done in a laboratory and determined the maxi- mum, practically achievable soil density at the highest possible water content and done under non-compacted conditions. In the field, working under compacted conditions limited the amount of water the soil could absorb. Additionally, the pad-foot roller ©2012 International Society of Arboriculture applied compaction pressure differently than the loaded, dump truck method potentially affecting only the upper soil layer. Se- nyk and Craigdallie (1997) found that soils responded differently to the use of various machinery and that water content at the time of activity was the critical characteristic in soil response. of ‘Fairview Flame’ ‘Frank’s Red’ 4972 a (a) 4228 a (a) 2667 b (a) 1580 b (b) C1 3642 a (ab) 2500 b (b) 1567 c (b) 1400 c (b) C2 2407 a (b) 2367 a (b) 2200 a (ab) 1238 b (b) L 2770 a (a) 2450 ab (a) 1920 bc (a) 1750 c (a) z Acer × freemanii ‘Celzam’ (Celebration Freeman maple, [n = 19]), Acer × freemanii ‘Morgan’ (‘Morgan’ Freeman maple, [n = 18]), Acer rubrum ‘Fairview Flame’ (Fairview Flame red maple, [n = 19]), and Acer rubrum, ‘Frank’s Red’ (Red Sunset red maple, [n = 16]), at the P ≤ 0.05 (Tukey’s honestly significant difference HSD). y Means followed by different letters indicate a significant difference between cultivars within each soil treatment (NC = non-compacted, C1 = compacted once, C2 = twice-compacted). x Means followed by different letters indicate a significant difference between cultivars within each pre-plant N treatments. Standard rate [H: 100 mg·L-1 Low rate L: 25 mg·L-1 or ] . Means followed by different letters within parentheses indicate a significant difference between the soil treatments or the pre-plant N treatments for each cultivar. Table 6. Mean leaf area values measured in the 2002 growing season for each cultivar (sample size in parentheses), show- ing responses to two different pre-planting nitrogen (N) rates. Cultivarz ‘Celzam’ (n = 17) ‘Morgan’ (n = 18) ‘October Brilliance’ (n = 10) ‘Bowhall’ (n = 17) ‘Fairview Flame’ (n = 18) ‘Frank’s Red’ (n = 16) Acer × freemanii ‘Celzam’ (Celebration Freeman maple), Acer × freemanii ‘Morgan’ (‘Morgan’ Freeman maple), Acer × freemanii ‘October Brilliance’ (‘October Brilliance’ Freeman maple), Acer rubrum ‘Bowhall’ (‘Bowhall’ red maple), Acer rubrum ‘Fairview Flame’ (Fairview Flame red maple), Acer ru- brum ‘Frank’s Red’ (Red Sunset red maple), Acer rubrum ‘Magnificent Magenta’ (Burgundy Belle red maple), and Acer rubrum ‘October Glory’ (October Glory ‘Magnificent Magenta’ (n = 17) ‘October Glory’ (n = 17) z red maple). y Means followed by different letters indicate a significant difference between cultivars within each pre-plant N treatment. Standard rate [H: 100 mg·L-1 rate [L: 25 mg·L-1], at the P ≤ 0.05 (Tukey’s honestly significant difference HSD). ] or Low Leaf area (m2 ) Pre-plant N ratey H 2.1 a 1.3 c 0.9 d 0.7 d 2.1 a 1.4 bc 1.0 cd 1.7 ab L 1.8 a 1.0 cd 0.7 de 0.5 e 1.3 bc 1.2 bc 0.9 dc 1.5 de
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