Arboriculture & Urban Forestry 33(2): March 2007 115 irrigated (FF); (8) fertilized each spring and fall (except at planting) with a split application and not irrigated (FSp); and (9) not irrigated or fertilized (NF). All trees were mulched with shredded hardwood bark in a ring extending approxi- mately 30 cm (1 ft) beyond the root ball. Rows were main- tained weed-free. Fertilizer applications were broadcast overa1m2 (10.8 ft2) area centered around each tree at a rate of 1.5 kg N/100 m2 (3 lb N/1000 ft2) and half that rate for each application in the FSp treatment. The fertilizer was a slow-release, sulfur- coated product from Southern States Cooperative, Inc. (Rich- mond, VA) with a 27 to 3–12 analysis (5.0% ammoniacal N, 1.8% water-insoluble N, 17.6% urea N, and 2.6% other water soluble N) described by the manufacturer as having a 4 month release time. Fertilizer was applied according to the treatment as follows: 31 March 2000 (at planting), Sept. 2000 (first fall), April 2001 (second spring), Oct. 2001 (second fall), April 2002 (third spring), and Oct. 2002 (third fall). All trees were hand watered for 2 weeks after planting. Subsequently, trees in unirrigated treatments received no supplemental water. In each irrigated treatment, soil moisture sensors (Watermark, Irrometer Co. Inc., Riverside, CA, U.S.) were installed 20 cm (8 in) deep inside and just outside of the root ball of three randomly selected replications. A given treatment was irrigated using drip emitters when soil tension reached 0.055 MPa (55 centibars) on two replications. A replication was considered to have reached this tension when one of the two sensors reached 0.055 MPa (55 centibars). This ensured that trees were irrigated before experiencing drought stress. Rainfall in Blacksburg during the 2000 and 2001 growing seasons was slightly below 30 year norms; for 2002, it was slightly above (Virginia State Climatology Office). Measurements Tree growth and nutrient status were monitored through three growing seasons to ensure that the entire establishment period was studied (Watson 1985). At the end of each growing sea- son, tree caliper readings were taken in two directions, along the row and across the row, and averaged for each tree. Cal- iper was used to calculate cross-sectional trunk area increase to give an integrated assessment of overall tree growth. Shoot extension during the 2000 and 2001 growing seasons was obtained by measuring new growth in February and March the next year before budbreak. The seven shoots nearest the top that showed the most growth (suppressed shoots, if any, were not included) were measured on each tree. Shoot exten- sion for each replication was taken to be the mean of the remaining five shoots after the two longest shoots were ex- cluded. Foliar nitrogen levels were determined in early sum- mer of the second growing season using four, randomly se- lected replications of each treatment. We selected five re- cently matured leaves from separate branches throughout the canopy of each tree selected and pooled them to make one sample. Percent nitrogen content was analyzed using the mi- cro-Kjeldahl method (Peterson and Chesters 1964). To maxi- mize statistical power, only a priori (preplanned) questions of interest were formulated as linear contrasts. These a priori contrasts were analyzed by multivariate repeated measures within the GLM procedure of SAS (version 8; SAS Institute, Cary, NC, U.S.). RESULTS For the most part, fertilization did not affect cross-sectional trunk increase (Figure 1; P values for preplanned contrasts of repeated measures analysis shown in Tables 2 and 3), shoot extension (Figure 2, Tables 2 and 3), or leaf nitrogen content (Tables 2 and 3) of either maples or lindens. Among irrigated treatments, there is no evidence that fertilizer applications affected growth (Tables 2 and 3). Among fertilized treat- ments, there is little evidence that irrigation affected growth or other variables. Cross-sectional trunk area growth rates and shoot extension were low the first year. This transplant shock effect was most dramatic for lindens (Figures 1 and 2). Repeated measures analysis looks at the growth rate over time (i.e., how size moves through time) and therefore re- duces error that might be introduced by differences in initial tree size. Consequently, although spring-fertilized, irrigated red maples appear to have larger cross-sectional areas than other trees, the rate of growth (indicated by the slope of the lines in Figure 1) is similar to other trees (as indicated by the P values in Table 2). In lindens, leaf nitrogen content was higher for FSp trees than in those with other nonirrigated fertilizer regimes (FSP 2.39%, FF 2.07%, FSP 2.15%, FS2.08%) as indicated by the contrasts in Table 3. The line slope (Figure 1) for FFI red maples between 2000 and 2002 is different from that of other treatments, indicating they grew at a slower rate than other treatments during that period. This is also confirmed by the contrast shown in Table 2(P 0.014) between fall and spring fertilization for irri- gated red maples. Because FSI red maples show a similar decline in growth rate between 2002 and 2003, however, spring fertilization does not appear to be consistently more effective. Both red maples and lindens with FFI treatment had lower average shoot extension in 2002 than their spring fer- tilized counterparts; however, these differences are slight and may be the result of factors other than treatment. DISCUSSION The A300 fertilization standard emphasizes that trees should only be fertilized when there is a defined objective. The fer- tilization objective in this study was to speed the establish- ment of shade trees. Posttransplant growth of shade trees typically increases annually during the establishment period (Harris and Gilman 1991), so rapid establishment can accel- ©2007 International Society of Arboriculture
March 2007
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