Restoring productivity of compacted forest soils with tillage Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6395w979j

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  • Tillage of forest soils compacted by ground-based logging systems is a practice that is becoming widely accepted in the Pacific Northwest. However, past research has failed to adequately define the conditions and specifications that particular tillage operations should meet in order to produce the maximum growth response from planted seedlings. The objective of this study is to quantify the early growth response of conifer seedlings to altered soil conditions produced by conventional ripping practices. To achieve the stated objective, a field study and a growth chamber study were implemented. A small tractor equipped with two 58-cm long ripper teeth spaced 140 cm apart performed the tillage on compacted gravelly loam soils in the Cascade Mountains of southwestern Oregon. Conditions for both studies included undisturbed soil, compacted soil in skid trails, and ripped soil in skid trails. Fifty-nine soil cores (15 cm in diameter by 32 cm long) were extracted from each treatment as growth media for the growth chamber study. Preliminary results from the field study shoved no significant differences in height growth or diameter growth of planted 2-0 bare root Douglas-fir (Pseudotsuga menziesii (Nirb.) Franco) seedlings after two years, even though soil bulk density and strength were significantly different and depth of compaction extended to 40 cm. It is possible that improper handling of seedlings either in the nursery or during planting has retarded development to the point that planting shock is overriding any effects.due to soil treatment. This phase of the study will be continued for another four years, so treatment effects may yet appear. The growth chamber study included observations on Douglas-fir and white fir (Abies concolor) seedlings grown from seed for 226 days. At 148 days, the Douglas-fir seedlings growing in tilled soil showed a 44 percent improvement in height growth compared to seedlings growing in compacted soil. Differences between means were statistically significant at p = 0.051 level. Differences between means for white fir were statistically significant at p = 0.074 level. Significant differences in root development were evident for both species at the end of 226 days. Dry root weight found in the top 20 cm of tilled soil for white fir was 61 percent greater than for trees growing in compacted soil. For Douglas-fir, a 42 percent increase was noted. These differences reflect the influence of aggregate strength rather than bulk density since the latter values for soil in the cores were not significantly different as a result of disturbance from sampling and handling. It was postulated that seedlings growing in tilled soil with their more extensive root systems would fare better under Stressed conditions than seedlings growing in compacted soil.
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  • description.provenance : Submitted by Anna Opoien (aoscanner@gmail.com) on 2008-11-21T23:47:21Z No. of bitstreams: 1 Whitaker, Carol A_1983_MS.pdf: 402758 bytes, checksum: d52a1efe395da38c74c751f2ba81be9b (MD5)
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2008-12-03T21:51:06Z (GMT) No. of bitstreams: 1 Whitaker, Carol A_1983_MS.pdf: 402758 bytes, checksum: d52a1efe395da38c74c751f2ba81be9b (MD5)

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