272 Statistical Analyses Statistical analyses were conducted using SAS JMP 7.0 soft- ware (SAS, Inc., Cary, North Carolina, U.S.). Data distribu- tions were checked for normality using the Shapiro-Wilk W test. Transformations of non-normal data were performed with log10, natural log, square root, or exponential functions. The treatment effects were analyzed using Analysis of Vari- ance (ANOVA). A sequential Bonferroni inequality was ap- plied to the critical p values to control for false positives (Type I error) associated with multiple testing (Rice 1989). Mean separations were carried out with Tukey-Kramer HSD tests. RESULTS AND DISCUSSION Soil Type Effects Significant effects were detected for soil type on all soil proper- ties (Table 2). The A horizon soils had lower pH, Ca2+ Na+, and higher Mg2+ , K+ PMN, and RES compared to soils from the Bt horizon. Treat- ment by soil type interactions were detected for NH4 , P, total C, total N, NH4 +, NO3 + (Table 2). Soil pH, Ca, Mg, K, Na, and P Soil pH was not significantly different in any treatments in either soil type (Table 2). Ammonium addition to soil re- sults in acidification because two H+ are generated with tion (Follet et al. 1981). Evolved CO2 from microorgan- to solution, also acidifying soil. Rela- the oxidation of each NH4 + ion in the process of nitrifica- isms reacts with water to form bicarbonate, and in the process releases H+ tive to water, neither fertilization nor ACT appeared to acidify these soils to produce measureable changes in soil pH. Nonresponses in pH were likely due to high buffering capacities of these silt and clay loam soils (Kelsey 2000). With the Bt horizon soils, Ca2+ was significantly greater with rizon soils. No differences were observed for soil Mg2+ decrease with fertilizer and ACTc (Table 2). Soil Ca2+ did not differ among treatments for the A ho- among the water and ACTd treatments for either soil type. Researchers in this study surmise that the Ca2+ is a result of micro- bial Ca2+ immobilization, since nitrifying bacteria are known to have a high requirement for calcium (Follet et al. 1981). Calcium is primarily applied to soils to change conditions related to its re- action, while Mg2+ cy. Finck (1982) suggests urban soils are rarely deficient in either Ca2+ or Mg2+ . Deficiencies of Ca2+ is applied to correct a plant nutrient deficien- and Mg2+ for crops are expect- ed to occur at approximately 500 and 50 mg kg-1, respectively, which were well below this study’s measured values (Walsh and Beaton 1973). It is believed that these soils were not deficient in either of these nutrients. Similar to these results, Hargreaves et al. (2008) found no differences in soil Ca2+ and Mg2+ contents one and two-years after applying fertilizer and non-aerated com- post teas made from municipal waste and ruminant compost. In the A horizon soil, K+ pared to other treatments (Table 2). Soil K+ levels in the A ho- and was greater with the ACTc com- rizon soils were greater with fertilizer compared to ACTd water (Table 2). No differences for K+ were observed with the Bt horizon soils, which had significantly higher K+ con- centrations (197 to 205 mg kg-1) as compared to the A hori- ©2011 International Society of Arboriculture treatment compared to the fertilizer treatment , and -, DON, MBN, Scharenbroch et al.: Biochemical Properties and Dentrification in A and Bt Soils zon soils (118 to 134 mg kg-1 greater than 170 mg kg-1 K+ ). Plants growing in soils with have been found to be nonrespon- sive to K+ fertilization (Walsh and Beaton 1973). Hargreaves et al. (2008) found soil K+ levels to be lower with non-aerated compost teas as compared to inorganic fertilizer, but this was likely due to the compost teas being applied as foliar sprays and fertilization as a soil application. The amounts of K+ ) exceeded that in the 30-10-7 fertilizer (117 in mg kg-1) (Table 1). Several studies report increases in soil K+ may also be an ef- ACTc (164 mg kg-1 from compost (Giusquiani et al. 1988; Bar-Tal et al. 2004). This study’s findings indicate that ACTc Sodium concentrations were not impacted by any of these treatments (Table 2). High Na+ Na+% > 10, which is Na+ fective method of increasing the soil available supply of K+ levels (exchangeable . ions) are detrimental to soil tilth and plant growth (Marx et al. 1996). In this study, the exchangeable Na+ divided by the sum of other cat- % values were all <2%, and so the amendments added to these soils do not ap- pear to present potential soil quality or tree health problems. Soil P with the A horizon soil was greater with fertilization compared to other treatments (Table 2). No differences were ob- served among the treatments for soil P with the Bt horizon soils, possibly a result of Ca-P precipitation at these higher pH values (Essington 2003). Annual P use for five southwestern Wiscon- sin tree species of varying leaf longevities ranged from 6 to 13 kg P ha-1 (Son and Gower 1991). Values of less than 5 mg kg-1 for the Bray P test suggest very low corn yields in Minnesota (Rehm et al. 2006). Only the fertilizer treatment increased levels of soil P to the range of P usage reported by Son and Gower (1991) and above the >5 mg kg-1 mg kg-1 P equating to 15 kg P ha-1 P requirement for corn (6.1 , assuming 1.0 Mg m-3 and 0.25 m depth) (Table 2). Similar amounts of P were contained in the fertilizer and ACTc treatment (Table 1). Researchers in this study suspect greater microbial P immobilization with ACT compared to fertilizer. Phosphorus immobilization is great with organic materials low in P content relative to energy sources (i.e., C contents) (Sauchelli 1965). The C/P ratio of the ACTc was 18/1 compared to the 8/1 for the fertilizer treatment. Assuming soil pH is not limiting P availability, fertilization appears to be more effective than ACT at increasing P levels in A horizon soils. Soil C and N No differences were observed in total C or N in either soil type with these treatments (Table 2). Total C and N are rela- tively stable pools, so researchers in this study did not expect these one-time treatments to have significant effects after only 10 days. Soil C has been thought to increase with fertilization by increasing the input of plant residues. However, recent re- sults from the Morrow Plots, the world’s oldest experimental site under continuous corn (Zea mays L.), indicate that after 40 to 50 years of synthetic fertilization that exceeded grain N removal by 60% to 190%, a net decline occurred in soil C despite increasingly massive residue C incorporation (Khan et al. 2007; Mulvaney et al. 2009). The decline in soil C with long-term fertilization was attributed to the excess fertilizer N promoting the decomposition of residues and soil C. To date, no studies have investigated the long-term impacts on soil C and N storage of fertilization or ACT application to urban trees. Soil NO3 - (Bt horizon only) and DON were greater with the fertilizer compared to the ACT treatments and water controls
November 2011
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
