Arboriculture & Urban Forestry 33(6): November 2007 431 gested that inoculum levels as high as 30,000 spores/m2 should be applied to the root zone to encourage mycorrhizal colonization during early root development in agricultural settings (Menge and Timmer 1982; Nelson 1987). It seems unlikely that changes in root diameter observed in the present experiment were related to added mycorrhizal spores. In conclusion, there was no evidence to suggest that Ter- ravent treatment stimulated fine root growth in a compacted soil. This result is consistent with previous reports citing little benefit from air injection devices. Treatment with a liquid soil amendment altered root diameter distribution and asso- ciated parameters, but the mechanisms and physiological consequences of these changes remain to be characterized. LITERATURE CITED Figure 2. Percent of fine root length in each of 19 diameter classes, from less than 0.1 mm to 1.9 to 2 mm (0.076 to 0.08 in). Fine roots (less than 2 mm [0.08 in] in diameter) were obtained from soil cores removed from areas treated with and without a liquid soil amendment. n = 20 for each treatment group. *P < 0.05. parameters. Root surface area, which is a function of length and diameter, was reduced in product-treated soil (Table 1). The absolute value of this difference was quite small: 0.01 cm2 (0.002 in2) per cubic centimeter of soil. Root mass, which decreases per unit length as root diameter decreases (assuming no change in tissue density), was also reduced (Table 1). Again, the magnitude of the reduction was small: approximately 2 mg per cubic centimeter of soil. Whether changes of this magnitude would be biologically relevant to a tree whose entire root system were treated the liquid amend- ment is unknown. Reductions in root surface area and mass may have altered the tree’s capacity for water and nutrient uptake in treated soil. However, nutrient uptake is a function of numerous parameters: nutrient availability and mobility in the soil, the extent of mycorrhizal colonization, the surface area of roots and mycorrhizal hyphae, and the affinity and velocity of membrane transporters. Factors governing rates of water in- flux are equally complex. Without information on changes in soil resource availability and root physiology associated with product application, it is difficult to assign functional signifi- cance to reductions in root mass and surface area. MycorTree Injectable contains a wide variety of biotic and abiotic ingredients, and the specific ingredient(s) responsible for reduced fine root diameter cannot be identified with cer- tainty. It is interesting to note that the number of endomy- corrhizal spores present in the prepared amendment was rela- tively low: 64 spores per 4 fl oz (0.12 mL) injection or 320 spores per 6 m2 (64.8 ft2) quadrant. Other authors have sug- Day, S.D., and N.L. Bassuk. 1994. A review of the effects of soil compaction and amelioration treatments on landscape trees. Journal of Arboriculture 20:9–17. Menge, J.A., and L.W. Timmer. 1982. Procedures for inocu- lation of plants with vesicular–arbuscular mycorrhizae in the laboratory, greenhouse and field. In N.C. Schenk (Ed.). Methods and Principles of Mycorrhizal Research. American Phytopathological Society, St. Paul, MN. Nelson, S. 1987. Rooting and subsequent growth of woody ornamental softwood cuttings treated with endomycorrhi- zal inoculum. Journal of the American Society for Horti- cultural Science 112:263–266. Patterson, J.C., and D.L. Mader. 1982. Soil compaction: Causes and control. In P.J. Craul (Ed.). Urban Forest Soils: A Reference Workbook. SUNY College of Envi- ronmental Science and Forestry, Syracuse, NY. Rolf, K. 1992. Soil physical effects of pneumatic subsoil loosening using a Terralift soil aerator. Journal of Ar- boriculture 18:235–240. ———. 1994. Soil compaction and loosening effects on soil physics and tree growth. In G.W. Watson and D. Neely (Eds.). The Landscape Below Ground. International So- ciety of Arboriculture, Savoy, IL. Smiley, E.T. 1994. The effects of soil aeration equipment on tree growth. In G.W. Watson and D. Neely (Eds.). The Landscape Below Ground. International Society of Ar- boriculture, Savoy, IL. ———. 2001. Terravent: Soil fracture patterns and impact on bulk density. Journal of Arboriculture 27:326–330. Smiley, E.T., G.W. Watson, B.R. Fraedrich, and D.C. Booth. 1990. Evaluation of soil aeration equipment. Journal of Arboriculture 16:118–123. USDA-NRCS. 1999. National Soil Survey Characterization Data. Soil Survey Laboratory. National Soil Survey Cen- ter, Lincoln, NE. ©2007 International Society of Arboriculture
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