180 Gilman and Marshall: Fertilizer Rate and Number of Applications Impact Growth of Trees data for the 2005 growing season were not reported because all trees were not measured at planting. Fertilizer Treatments Treatments included a non-fertilized control (zero rate) and 16 combinations of fertilizer amount (reported as rate) and application timing (report- ed as frequency). Fertilizer was surface-applied to a circular soil area centered on each trunk, using a customized cup appropriately sized for each treatment, beginning March 2005 through August 2008. The traditional or historical annual rate used by the nursery, and generally recom- mended for field nurseries in that part of Florida, was designated the 1.0 historical rate, which was 284 g applied around each tree in Year 1 (2005), 908 g in Year 2, and 1090 g in Years 3 and 4. The increasing amount is thought to accommodate increase in tree size. Growers typically divide fer- tilizer into three equal amounts applied about March, May/June, and July/August. This served as the benchmark for comparison. Annual amounts equal to one-third (0.33), two-thirds (0.66), and one-and-one-third (1.33) historical comprised the remaining rates. These four amounts were applied either all at once in May; divided into two equal amounts and applied in both March and June; di- vided into three equal amounts and applied March, May, and July; or divided into four equal amounts and applied in March, April, June, and August. The custom blended granular fertilizer (Graco Fertilizer Company, Cairo, Georgia, U.S.) was an 18 N, 1.76 P, 6 K derived from 49% water insolu- ble N (from sulfur coated urea and activated sew- age sludge) and 51% soluble N (from ammonium nitrate and diammonium phosphate) equivalent to 51, 163, 196, and 196 g N/tree annually for the 1.0 rate for 2005, 2006, 2007, and 2008, respec- tively. The circular area fertilized was 0.65 m2 for all years. The result was a 1.0 historical annual rate of 78, 250, 302, and 302 g N/m2 for Years 1, 2, 3, and 4, respectively expressed on an applied area basis. However, only 1.3% of the field plot surface received fertilizer (i.e., the 0.65 m2 circular area around each trunk); therefore, when expressed on an entire field plot basis, the 1.0 historical rate was 1.0, 3.25, 3.93, and 3.93 g N/m2 for Years 1, 2, 3 and 4, respectively. Another way to report the histori- cal rate is N applied per unit (cm) caliper for Ilex ©2014 International Society of Arboriculture (41, 36, and 25 g N/cm caliper) and for Quercus (35, 29, and 21 g N/cm caliper) using caliper measured at the end of 2006, 2007, and 2008, respectively. Application Procedures Signs were installed at the four corners of the test plot stating, “Do not fertilize between signs.” Combined with a sign in the middle of the north and south borders, the six signs instructed nurs- ery personnel not to fertilize over the test during normal fertilizations of the nursery. Fertilizer was applied beginning at the southwest corner work- ing northward and down a double row. Each plot of 10 trees was labeled by a vertical wood stake 1.5 m tall, instructing the farm manager as to the month to apply fertilizer, which scoop to use, and how many of these scoops to apply. Pre- calibrated customized scoops were of appropriate volumes to deliver the correct fertilizer amount when filled to the rim. Each had a unique label matching that of each stake in the field (e.g., the label “5- 3- A” meant for fertilization in May and the application of three of the ‘A’ scoops). Experimental Design and Statistical Analysis All trees of one species were placed together in one field; those of the other species began 3.6 m away in an adjacent field. Species comparisons were not included in the analysis. Trees were in a random- ized complete block design with four blocks. Each block contained 17 plots, one for each treatment, containing 10 trees each that received a similar treatment grouped together in two adjacent rows of five trees spaced 1.8 m apart within rows × 2.4 m apart between rows. The 17 treatments ran- domly assigned to plots of 10 trees were four fertil- izer rates (five, including non-fertilized control) × four frequencies. There was a 3.6 m section with- out a tree along the row to separate each plot of 10 trees. Therefore, each plot had a non-fertilized buf- fer of 3.6 m on all sides. Data were analyzed using SAS with two-way ANOVA in a split plot in time. Data normality and equal variances for both species passed the tests performed within the Univariate procedure in SAS. Means were separated using LS Means. Pearson’s correlation coefficients (r) were calculated to test significant associations. Values were considered statistically significant at P < 0.05.
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