Arboriculture & Urban Forestry 36(6): November 2010 cycle was started the day after treatment, and DTW was recorded for each seedling using the methodology previously described. DTW data from both the 2007 and 2008 trials were analyzed as randomized complete block designs using an analysis of vari- ance (ANOVA). Because there were no PPS yellow-poplar seed- lings available, the design is unbalanced for the 2008 trials. For each year, the study authors fit an ANOVA model containing all significant and estimable main effects and interactions. For the 2007 trials, treatment, species (red maple; red oak), produc- tion type (PPS; BRS), and the interaction between species and production type, were included in the model. For the 2008 tri- als, only the main effects were both estimable and significant. Models were fit and analyzed using the statistical software packages Minitab (version 15; State College, PA, U.S.) and R. Differences in treatment means were compared using Tukey’s pairwise comparison test at significance levels of 0.01 to 0.05. Graphic analyses of the data were prepared as side-by-side box plots (Moore and McCabe 2002) where each box bisected by a line represents the median value bounded by both upper and lower quartiles. Verti- cal lines at the top and bottom of each box indicate the range of data and illustrate important differences that exist between treatments. Box plots provide a graphical comparison of groups of numbers, and are used to visually compare “within treatment variation” with “between treatment variation” in a manner analogous to ANOVA. RESULTS AND DISCUSSION In analyzing the data for the 2007 trials, it was revealed the es- timated increase in DTW for both species (red maple and red oak) and both production types (PPS and BRS) was 9.2 days for HydES applied at the recommended rate (16 mL/L) and 10 days for HydES applied at twice the recommended rate (Fig- ure 1). Both values were highly significant (P < 0.01). These results show that doubling the application rate of HydES has little impact on DTW (9.2 versus 10 days), and is probably not cost effective under most circumstances. HydES applied at a concentration of 8 mL/L (half the recommended rate) was only marginally effective, increasing DTW by 3.9 days (P < 0.05). Overall, the results of the 2007 trials indicate that HydES can be 277 an effective product for extending the irrigation cycle of drought stressed red maple and red oak seedlings when applied as a soil drench at the manufacturer’s recommended rate (16 mL/L). Data for the 2008 trials (Figure 2) illustrate treatment with either HydES or EcoS successfully extended DTW for humec- tant-treated seedlings of both PPS and BRS red maples and BRS yellow-poplars. Compared to the untreated controls, the estimated increase in DTW was 8.6 days (P < 0.01) for HydES applied at the recommended rate (X), and 4.7 days (P < 0.05) for HydES applied at a rate of 0.75X. For EcoS, the estimat- ed increase in DTW was 8.1 days (P < 0.01) for humectant- treated seedlings at the recommended rate (X), and 6.5 days (P < 0.05) at a concentration of 0.75X. These results indicate both humectants, when applied in the range of 12–16 mL/L, can extend DTW for treated, drought stressed seedlings of red maple and yellow-poplar. The results of these trials also indi- cate there were no appreciable differences in the effectiveness of the two products at the concentrations used in these studies. Figure 2. The effect of two media-applied humectants [Hydretain ES (HydES) and EcoSential (EcoS)] on number of days to wilt of one-year-old drought-stressed red maple and yellow-poplar seedlings representing different production types [peat plug sys- tem (PPS); bare-root system (BRS)]. Treatments 1: no chemical; 2: HydES at 16 mL/L (X); 3: HydES at 12 mL/L (0.75X); 4: EcoS at 16 mL/L (X); and 5: EcoS at 12 mL/L (0.75X). Altering root ball shape can have a dramatic effect on root Figure 1. The effect of media-applied humectant [Hydretain ES (HydES)] on number of days to wilt (DTW) of one-year-old drought-stressed red maple and red oak seedlings representing different production types [peat plug system (PPS); bare-root system (BRS)]. Treatments 1: no chemical; 2: HydES at 8 mL/L (0.5X); 3: HydES at 16 mL/L (X); and 4: HydES at 32 mL/L (2X). growth potential (Struve et al. 1989), and as a result, on the abil- ity of a plant to absorb moisture from the soil. Table 1 compares DTW for humectant-treated seedlings representing the two production types found in these studies. In 2007, the number of days to wilt was significantly greater for BRS maples than for PPS maples at all concentrations of HydES tested. And, in similar trials conducted the same year, BRS oaks treated with HydES at 16 mL/L (the recommended rate) also showed sig- nificantly higher DTW values than did comparably treated PPS oaks. These data suggest BRS seedlings of red maple and red oak may be somewhat more responsive to humectant treatment than are comparable sized PPS seedlings of the same species, but additional studies are needed to confirm these observations. Daily media moisture readings taken on PPS maples dur- ing the 2008 experiments show that, starting the first week af- ter treatment and continuing for the duration of the drought cycle, the moisture content in humectant-treated substrate was ©2010 International Society of Arboriculture
November 2010
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