Seedlings from bare-root forest nurseries are used in the conservation and reforestation in the North Central Region of the United States. To kill root disease caused by bacteria in these nurseries, managers have relied on methyl bromide (CH3Br) as a fumigant since about 1960 because of its ability to kill any organic pathogen. However, methyl bromide has been found to be a dangerous gas because it acts like a chlorofluorocarbon that depletes the ozone layer of the atmosphere. In fact, bromine may be a more potent destructive agent. Also, methyl bromide is very harmful to people who are applying it in the nurseries. Therefore, various other chemical agents have been considered as alternatives to methyl bromide. Dazomet (tetrahydro- 3,5, dimethyl-2H-1, 3, 5-thiadianzone-2-thione) is one such chemical that has been tested and considered to be the best alternative for the future, primarily because of lower toxicity. Another problem with methyl bromide relates to its application process. Fumigation is tedious, costly and labor intensive. Therefore, alternative forms of application are always being sought. Currently, dazomet also has the requirement to be applied as a fumigant. The research done by my research mentors, R.R. Allmaras and S.M. Copeland, and other researchers (1997, 1998) over the last five years, has been searching to see if applying a chemical agent like dazomet in the solid form to incorporate into the soil would be a viable solution. Instead of applying the pesticides, tracer spheres were used as a substitute, applied on the surface and then incorporated into the soil by tillage as a possible better alternative to fumigation. The goal of the research done was to concur with the hypothesis that the tillage machines would incorporate the tracer spheres with enough ability to efficiently saturate the soil with an agent such as dazomet.
To achieve maximum efficacy of distribution of the tracer spheres, they must achieve uniformity to a pre-determined target depth. The target depth for the procedures used is 0-30 cm. The tillage machine with the greatest uniformity through the plot in the soil depth range will be the most efficient. The four tillage machines used, Kuhn EL80N, Fobro Kultipack 1700, Northwest Tiller DHC-96-SC, and Gramegna V84/30B, were each used over a 5 ft X 10 ft plot area. The hypothesis of this research was that the Gramegna V84/30B spading machine would produce the greatest uniformity through the desired 0-30 cm soil depth.
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The hypotheses for the research done were that a machine would efficiently incorporate the tracer spheres used in the procedure. In addition, that a machine would uniformly incorporate the tracer spheres throughout the desired depth range of 0-30 cm.
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Procedure
Ceramic spheres, as tracers, were incorporated by four test tillage implements to obtain information on uniformity and maximum depth of incorporation in the 0-30 cm soil layer. Each tillage implement was assigned to one of five treatment columns (each 3.7m X 76m) within the same field (figure 1). The first 30m of implement area was used to establish a consistent and measured tractor speed and to correct tillage implement settings. Fluorescent green or red ceramic spheres (Macrolite TM ceramic spheres, Industrial Mineral Products Division/3M, St. Paul, MN, of 1-3 mm diameter and mean mass of 3.72 mg per sphere, were applied (6.2 beads cm^-2) on the raked soil surface of two selected plots (approximately 2m X 3m depending on width of assigned tillage implement) in each treatment column (figure 2). Tracers were broadcast using a hand operated drop-type spreader (figure 3). Several passes perpendicular to each other were made over the entire plot to reduce the variability of application. The tracer spheres were applied and tillage was performed on different dates in mid- to late-June 1994 (figure 4 and figure 5). Three rotary tillers and a spading machine were used at recommended speeds and PTO revolutions per minute to incorporate the spheres.
Soil samples from all plots were taken 1 week after tillage using a tube sampler (figure 6). Cores were systematically taken using a wooden template, transversely placed (37 degrees offset) across each plot (figures 7 and figure 8). Sampling holes (19mm diameter) in the template were 4cm apart, on center. Depending on operational width of each implement, a minimum of 39 cores (18mm diameter) were taken to a depth of 30cm across each transect. Each core was sectioned into 2-cm increments and samples were stored in separate paper envelopes until processed. Samples were oven-dried and broken apart to recover and count spheres. The total number of spheres recovered per transect was apportioned by their presence in each of the 15 increments in the top 30 cm.
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Results
Table 1 is an example of the spreadsheets used to record results during experimentation. Graph 1 and graph 2 were made with a program called Surfer. They clearly show that the Gramegna spading machine was superior to the other tillage machines used.
| Table 1 | ||||
Site: Hayward, WI |
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|---|---|---|---|---|
| EQUIP | Transect # | Beads/cm^3 | Core # | Depth (cm) |
Fobro |
39 | 2.79 | 42 | 29 |
| 40 | 3.35 | 42 | 29 | |
| 41 | 5.77 | 42 | 29 | |
| 42 | 4.09 | 42 | 29 | |
Gramegna |
35 | 2.6 | 39 | 29 |
| 36 | 1.3 | 39 | 29 | |
| 37 | 2.23 | 39 | 29 | |
| 38 | 1.67 | 39 | 29 | |
Kuhn |
31 | 8.37 | 48 | 29 |
| 32 | 3.91 | 48 | 29 | |
| 33 | 4.46 | 48 | 29 | |
| 34 | 6.51 | 48 | 29 | |
NWTiller |
43 | 4.84 | 60 | 29 |
| 44 | 9.3 | 60 | 29 | |
| 45 | 8 | 60 | 29 | |
| 46 | 5.77 | 60 | 29 | |
To reach ideal uniformity and incorporation there would have been two to six beads found in every 2 cm depth core, down to 30 cm. The Gramegna V84/30B spading machine was the closest to these ideals with an average of one to seven beads for every core, down to 25 cm. The second closest to the ideal was the Northwest Tiller DHC-96-SC. However, all three rotary tillers that used vertical action, forward rotation with L-shaped tines (Kuhn EL80N, Fobro Kultipack 1700, Northwest Tiller DHC-96-SC) showed an inferior incorporation ability to the crankshaft type Gramegna V84/30B spading machine. The rotary tillers showed highly concentrated clusters throughout the plot area, however the Northwest Tiller DHC-96-SC resulted in deeper occurrences of these clusters.
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Conclusion
The goal of the research was to find the tillage machine with the best ability to uniformly distribute tracer spheres to a predetermined soil depth. We found that the Gramegna V84/30B distributed the spheres with the closest uniformity to the desired. The Northwest Tiller was second best but contained highly concentrated clusters throughout. Therefore, the hypotheses were correct, and the Gramegna V84/30B is the best tillage machine for future distribution of a Methyl Bromide alternative.
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