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| ABSTRACT We investigated how cranberry vines covered with snow during a Maine winter would survive compared to vines covered with water (and eventually ice). Eight plots measuring 6 ft2 were selected from a 2½-acre commercial cranberry bog for the study. Three plots were chosen to be covered with snow. Another three (all at a slightly lower elevation) were chosen to be under the winter flood. The remaining two plots, located at an elevation above the winter flood, were selected to serve as control plots (receiving no treatment of any kind). Bud Health: A microscopic bud health assessment was performed in November of 1998 on each of the six test plots prior to any treatment of snow or water. At that time, there was no significant difference (95% confidence level) between the proportion of buds that were alive (with no apparent damage) from the plots slated for snow and those slated for water. However, by May 3rd of 1999, following the treatments of snow or water, there was a significant difference between the proportion of buds that were alive and not noticeably damaged from the snow plots versus the flood (water/ice) plots. There was also a significant difference between the snow-covered plots and the two control plots. Analysis of variance further supported the conclusion that the treatment used (ice, snow or “Mother Nature”) affects the number of buds that will survive the winter without noticeable damage. When buds were taken from all eight plots on May 4th of 2000, no significant difference was seen between the proportion of buds that survived the winter undamaged from the snow plots versus the flood (water/ice) plots. As expected, there was a significant difference in bud damage between the flood (water/ice) plots and the two “Mother Nature” plots each year of this study. Bud Size: Lastly, bud size (> or < 1 mm. wide) was significantly different between the snow plots and the flood plots on May 3rd of 1999 but not on May 4th of 2000. |
| IN RECENT YEARS, the State of Maine has experienced below
average rainfall amounts, particularly during the summer months (Table
1). In 1994 and 1995, for example, the state received 14% and 30% less
rain than normal, respectively, from June through September. The
summer of 1999 was another dry one for Maine: 23% below
normal rainfall, totaling just 8.42”.
1 University of Maine Cooperative Extension (Cranberry
|
The least amount ever measured since 1895 was 7.49”, recorded in 1948
(Northeast Regional Climate Center: Cornell University). The 7.64”
which fell in 1995 was barely more than the record minimum! This
lack of rain has often found cranberry growers in Maine with insufficient
water for wet-harvesting and for the subsequent winter flood.
For this reason, the question arose as to whether cranberry vines covered with snow during the winter could fair as well, if not better than, vines covered with the traditional winter flood (and eventually ice). |
Table 1. Summer (June-August)
Maine Precipitation Averages.
Source: Northeast Regional Climate Center: Cornell University.
Source: Northeast Regional Climate Center: Cornell University. Materials and Methods Methods: The same day each Fall (1998 and 1999) that the winter flood was applied to the three “flood” plots, snow was added to the three “snow” plots to a depth of 3 in. Anytime that there was not enough natural snow to maintain a depth of at least 3 in., then additional snow was shoveled onto the plots as a result of having plowed the driveway and accumulated the resulting snow into a large pile. The pile, which was located roughly 10 ft. away from the test plots, was kept covered with a light-reflecting tarp to conserve as much snow as possible. The few times when there was no longer any snow to be found, man-made crushed ice was applied to the snow plots. On November 16, before any treatments had been applied, 50 tips were collected from each of the six test plots. The buds were examined with a dissecting microscope and scored as either alive (with no apparent damage), noticeably damaged, or dead. A bud was considered to be dead if the inside, including the apical meristem, was predominantly black in color. If there was a mixture of black and green inside the bud, but the apical meristem was mostly or entirely green, then the bud was scored as “noticeably damaged.” The 1998/99 winter flood was removed during the last week of April, 1999. On May 3rd, 50 tips were again collected from each of the six test plots, as well as the two control plots, and were scored the same way as in November. The size of each bud was also recorded as either small (< or = to 1 mm. wide) or large (> 1 mm. wide). This was repeated on May 4th of 2000. Each year, the plot identities of the samples were kept secret until after the microscopic bud health assessments had been performed in order to eliminate potential bias. A max-min thermometer was used to periodically monitor the air, snow and water/ice temperatures. The “Difference between Proportions” test was used in order to test: 1). the significance (from one group of plots to another) of the number of buds that were alive in the Fall of 1998 (before any treatments were applied), 2). the number that survived the two winters from one set of plots relative to another, and 3). the size of the buds from one set of plots relative to another. A significant difference between proportions means that there is a small chance that the proportions would be equal if you took different random samples of the same sizes. Analysis of variance (ANOVA) was used in accordance with a randomized complete block design* in order to analyze the bud health data. * The blocks could not be randomized in relation to the treatments since the snow plots and control plots had to be at a slightly higher elevation than the flood plots. Since there were only two control plots and thus a missing "block" in the ANOVA table, the missing value had to be estimated such that the error sum of squares in the ANOVA could be minimized. Differentiation was used to achieve this minimization. Flood (ice) Plots vs. Snow Plots: In 1999, the difference in bud survival between the flood and the snow plots was significant: 93% of the buds from the flood plots were still alive and had no apparent damage compared to just 76% from the snow plots (n = 300, zTest = 4.17, P < 0.05). But in 2000, the difference in proportions between the flood and snow plots was not significant: 90% undamaged buds from the flood plots versus 84% from the snow plots (n = 300, zTest = 1.54, P > 0.05). |
- Results continued -
Snow Plots vs. Control Plots: The snow
plots faired significantly better than the two control plots that were
left to “Mother Nature” during the winter of 1998/99. Only 48% of
the buds taken from the control plots in 1999 were undamaged (n = 250,
zTest = 4.54, P < 0.05). This percentage jumped to 79% undamaged,
however, following the winter of 1999/2000, and so when compared to the
84% of buds from the snow plots that survived undamaged, there was no significant
difference (n = 250, zTest = 1.01, P > 0.05).
Bud Size. The proportion of buds larger than
1 mm. in size was significantly different between the snow plots and the
flood plots in 1999 (n = 300, zTest = 4.17, P < 0.05), but not in 2000
(n = 300, zTest = 0.81, P > 0.05).
Maine experienced daily temperatures from December of 1998 to March of 1999 that were, on average, 4.1 degrees F warmer than normal. In fact, the average daily temperature of 20.5 degrees F was rather close to the warmest average daily temperature ever recorded since 1895: 23.5 degrees F set in 1933 (Northeast Regional Climate Center: Cornell University). In addition, Maine received an average of 21% less snow (and/or mixed precipitation) than normal that winter (Table 2). Thus, it was probably difficult to keep at least 3 in. of snow on the snow plots at all times and hence there were likely times when the plots were completely exposed. This may have in turn given rise to the significant differences that were observed among the three treatment groups with regards to bud damage in the snow and control plots versus the flooded plots. Given that the 1999/2000 winter in Maine was only slightly colder than the previous winter (an average of only 1.6 degrees F colder) and yet received 98% of its normal allotment of snow (Table 2), one would expect to see less of a difference among the three treatments. And of course, no significant differences were seen when comparing the three of them together using ANOVA. When comparing the ice plots with the control plots, however, using the “Difference between Proportions” test, a significant difference was found. This was also the case in 1999. This finding helps substantiate the belief that flooding is the best method of winter protection for cranberries, even during winters of ‘normal’ snowfall amounts, which in Maine (9.24”) is slightly higher than in the northeast region as a whole (8.88”) (Northeast Regional Climate Center: Cornell University). References Cited http://met-www.cit. cornell.edu/nrcc_home.html Acknowledgments |
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