Arboriculture & Urban Forestry 40(6): November 2014 Table 2. Prob > F values for effect tests of treatment, spe- cies, and treatment*species using ANOVA standard least squares models for soil bulk density, soil moisture, pH, N, P, K, soil organic matter, and microbial respiration. Soil response Bulk density (Mg m-3 Total N (%) Bray P (mg kg-1 ) Exchangeable K (mg kg-1 Soil organic matter (%) ) Microbial respiration (mg kg-1 d-1 ) Gravimetric soil moisture (%) pH (1:1) Treatment 0.0116 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 ) <0.0001 Species Tr*Sp 0.7174 0.0590 0.8827 0.3304 0.9667 0.8466 0.9151 0.0025 0.4962 0.9538 0.3997 0.9330 0.9917 0.8702 0.1367 0.6508 moisture by 26%, increase SOM by 25%, increase RES by 33%, and increase K by 24%. The COMP treatment increased soil moisture +13%, SOM +57%, RES 39%, N +68%, P +1544%, and K +64%. Relative to the control, the FERT treatment only impacted soil P, which increased 286%. No differences were observed for these eight soil properties between the NULL treatment and ACT or CBP treatment. Both WC and COMP appear to be the most effec- tive treatments at improving soil quality. The WC treatment tended to be more effective at improv- ing soil physical condition (density and moisture), whereas the COMP treatment better improved soil biochemistry (SOM, RES, N, P, and K). It was expected that soil moisture would be great- est with the WC treatment. Wood-chip mulches would limit evaporation and also limit water uptake by competing vegetation (Watson 1988). Compost is a source of labile organic mat- ter and nutrients. It was expected and found that the COMP treatment would most increase organic matter and stimulate microbial activity. These increases in SOM and microbial activity appeared to, in-turn increase soil nutrient sup- plies of N, P, and K (Scharenbroch et al. 2013). The increases in soil P with COMP are concern- ing given the potential for P pollution of aquatic ecosystems (Carpenter et al. 1998). Precautions should be taken when using composts in urban landscapes to minimize runoff and erosion, which are major pathways of P loss to surface waters. The observed decrease in bulk density with WC treatment, and not with COMP treatment, was somewhat surprising. Biological activity is an important driver of soil aggregation, which would work to reduce bulk density and alleviate soil com- paction. The WC treatment increased microbial respiration but also had the most significant impact 325 on tree growth. Increases in soil moisture with the WC treatment may also have been important for facilitating root growth through these compacted urban soils and thereby increasing the extent of soil that roots and microbes would access. Together, increased microbial and tree root growth likely contributed to the observed decreased bulk density. Soil pH was expected to decrease with COMP and FERT treatments due to the pH-lower- ing effects of respiration and N mineralization (Sikora and Yakovchenko 1996). However, soil pH increased with compost and it may be that the compost increased base saturation by increasing Al complexation (Van den Berghe and Hue 1999). Tree Growth Responses Significant treatment effects were detected for total tree biomass, total shoot biomass, total root bio- mass, stem biomass, leaf biomass, and coarse root biomass (Table 3). Treatment effects were not sig- nificant for medium and fine root biomass. Spe- cies effects were significant for all tree responses except fine root biomass, and the treatment by species effect was only significant for leaf biomass. Table 3. Prob > F values for effect tests of treatment, species, and treatment*species using ANOVA standard least squares models for tree biomass fractions. Tree response Total biomass (g) Total shoot biomass (g) Leaf biomass (g) Stem biomass (g) Total root biomass (g) Coarse root biomass (>5 mm) (g) Treatment Species Tr*Sp <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.0006 Medium root biomass (2–5 mm) (g) 0.1544 Fine root biomass (<2 mm) (g) 0.2393 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 0.6841 0.1401 0.0319 <0.0001 0.1917 0.8981 0.7934 0.6990 0.2955 Given the minimal treatment by species effects, main treatment effects were examined by combin- ing both species. Total tree biomass and total stem biomass were significantly greater with WC, COMP, and FERT compared to ACT, CBP, and NULL (Fig- ure 1). Total stem biomass was also significantly greater with WC compared to FERT. Leaf biomass was significantly greater with WC compared all other treatments, and leaf biomass was greater with FERT and COMP compared to CBP and NULL. Stem biomass was significantly greater with WC, COMP, and FERT compared to ACT, CBP, and NULL. Coarse root biomass was significantly greater with ©2014 International Society of Arboriculture
November 2014
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