Arboriculture & Urban Forestry 37(6): November 2011 control soils. However, the study authors conclude that micro- bial respiration is, for the most part, greatest with fertilizer. Nitrogen mineralization was greater with fertilization com- pared to water and ACT treatments in both soil types (Table 2). Rates of N mineralization for the A horizon soils extended over a 180-day growing season would be: 86 (water), 162 (ACTd 216 (ACTc), and 396 (fertilizer) kg N ha-1 ), . Annual N require- ments for five tree species in southwestern Wisconsin were 38 for Pinus resinosa Ait., 80 for Pinus strobus L., 81 for Picea ab- ies (L) Karst, 86 for Larix decidua Miller, and 126 kg N ha-1 for Quercus rubra L. (Son and Gower 1991). Soil N in the fertiliza- tion treatment exceeded these reported tree N requirements by as much as ten-fold. Soil N in the ACT treatments exceeded tree N requirements by up to five-fold. Soil N with the water treat- ment appeared to best match estimated tree N requirements. In the Bt horizon soils, only the fertilizer treatment increased N mineralization (149 kg N ha-1 ) to a range close to meeting the kg-1) and 96 (+127 mg kg-1 tree N demands (Table 2). Nitrogen immobilization (i.e., nega- tive potential N mineralization) was measured in the Bt horizon soils for the water and ACT treatments. Increased soil N min- eralization is important for tree nutrition in urban soils, but N immobilization in the microbial biomass may also be important for nutrient retention in disturbed urban landscapes with a high propensity for nutrient losses to the hydrosphere or atmosphere. In the A horizon soils, it was found that N2 creased with fertilizer compared to ACTc O efflux in- at hours 48 (+65 mg ) of the 192-hour laboratory assay +12 mg kg-1 increase was five to 11 times less than the fertil- izer-associated N2O increase at hours 48 and 96 (Figure 1). At (Figure 1). At hour 12 in the A horizon soil, N2O efflux was greater with ACTc compared to fertilizer and water, but the hours 12 and 24 with the Bt horizon soils, N2O efflux was ap- proximately +4 mg kg-1 greater with ACT than water or fertil- izer. No differences were observed at hours 24 and 196 for the A horizon and at hours 48 and 192 for the Bt horizon soils. Environmental influences on denitrification include denitrify- ing organisms, pH, temperature, oxygen, moisture, oxidizable organic matter, and the amount of NO3 - with the fertilizer treatment explain the larger - present (Follet et al. increases in N2O efflux with fertilization in the A-horizon soils were a consequence of increased avail- tion, and proposed that the availability of N to soil organisms was the likely driving factor in greater spring N2 able dissolved organic C in the ACT (Table 1). The research- ers are aware of no other studies comparing denitrification responses of ACT and fertilization. Alluvione et al. (2010) found that compost application reduced the CO2 bined N2O and CO2 equivalent of com- the greatest absolute increases were observed with the fertiliz- er treatment in the A horizon soils (+65 to +127 mg N2 , (+4 to +12 mg N2 CONCLUSION Over these short-term laboratory assays, ACT appears inferior compared to fertilizer in its ability to increase microbial bio- mass, microbial activity, DON, NO3 -, and P in soil. These results following fertilization. Although the study authors observed in- creases in denitrification with ACTc efflux by 49% compared to urea fertiliza- O emissions O kg-1 O kg-1 ), ). at hours 24 and 48. The authors believe the initial denitrifica- tion increases with ACTc 1981). The researchers in this study suspect increases in read- ily available NO3 compared to water. In A horizon soils, NH4 equaled fertilizer, and K+ show ACTc , NH4 were observed with ACT compared to fertilizer showing great- er potential nutrient retention with ACT compared to fertilizer. Urban soils are often infertile and highly disturbed, so nutrient limitations and potential losses are pertinent considerations for arborists and urban foresters. This research shows that fertiliza- tion is more effective at increasing short-term soil nutrient avail- ability, but nutrient retention may be better preserved with ACT or water. The resource and application costs of water, ACT, and fertilizer must be weighed against the potential benefits these treatments may provide. The ACT contained only a fraction of the organisms found in the compost, and future research should examine compost and other organic fertilizer as soil amend- ments in comparison to ACT, synthetic fertilization, or water. compared to fertilizer. In the A horizon soils, the greatest poten- tial of surplus available N was observed with the fertilizer treat- ment. Only the fertilizer treatment appeared to deliver enough available N to potentially meet tree needs in the Bt horizon soils. Lower total N2 levels with ACTc O efflux and greater microbial immobilization Acknowledgments. The authors grate- fully acknowledge financial sup- port from the TREE Fund Hyland R. Johns Grant (08-HJ-02), and The Morton Arboretum Endowment. We thank the Morton Arboretum Soil Science labora- tory volunteers and student interns for their assistance. We thank the reviewers for their insightful critiques and com- ments provided during the preparation of this manuscript. LITERATURE CITED Alluvione, F., C. Bertora, L. Zavattaro, and C. Grignani. 2010. Nitrous oxide and carbon dioxide emissions following green manure and compost fertilization in corn. Soil Science Society American Journal 74:384–395. American National Standards Institute (ANSI). 2004. A300 Standard for tree care operations - tree, shrub, and other woody plant maintenance - standard practices (Fertilization, Part 2). American National Stan- dards Institute, New York, New York. Bar-Tal, A., U. Yermiyahu, J. Beraud, M. Keinan, R. Rosenberg, D. Zohar, V. Rosen, and P. Fine. 2004. Nitrogen, phosphorus, and potassium uptake by wheat and their contributions in soil following succes- sive, annual compost applications. Journal of Environmental Quality 33:1855–1866. Brookes, P.C., A. Landman, G. Pruden, D.S. Jenkinson. 1985. Chloro- form fumigation and the release of soil nitrogen: A rapid direct ex- traction method to measure microbial biomass nitrogen in soil. Soil Biology and Biochemistry 17:837–842. Chalker-Scott, L. 2007. Impact of mulches on landscape plants and the environment – A review. Journal Environmental Horticulture 25: 239–249. Corsi, S.R., D.J. Graczyk, D.W. Owens, and R.T. Bannerman. 1997. Unit- area loads of suspended sediment, suspended solids, and total phospho- rus from small watersheds in Wisconsin. U.S. Department of Interior, U.S. Geological Survey, Fact Sheet FS-195-97. Middleton, Wisconsin. Day, S.D., E.P. Wiseman, S.B. Dickinson, and R.J. Harris. 2010. Con- temporary concepts of root system architecture of urban trees. Arbo- riculture & Urban Forestry 36:149–159. to increase soil K+ 275 +, and microbial respiration + levels with ACTc were greater when ©2011 International Society of Arboriculture
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