Graduate Thesis Or Dissertation
 

Responses of Douglas-fir seedlings to various nursery handling and outplanting practices

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  • In study 111, four Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stocktypes (1-0, 2-0 standard nursery run and low density bareroot seedlings, and 1 year old container stock) were outplanted in a randomized incomplete block design to an old field in the Willamette Valley of Oregon in a factorial experiment t4 stocktypes x 2 lifting dates (November, January) x 2 levels of cold storage (none, 3 weeks at 2°C) x 2 types of planting hole/initial root configuration (slit, three-dimensional)]. Growth and survival were monitored for two years. A root pathogen was implicated in the high first year mortality of the 1-0 (50%), plug (20%) and November-lifted (50%) seedlings. Thereafter, the bareroot stocktypes achieved equivalent moderate increases in height, and stable rates of diameter and dry weight growth. Shoot length and diameter relative growth rates (RGR) were greatest for 1-0 bareroot stock. The higher elevation source container stock lagged behind the bareroot seedlings in height increment. November- and January-lifted seedlings performed equally well with two exceptions attributable to interaction effects. For the November-lifted stock, hole-planting led to increased height growth due to increases in both the number of the stem units formed during the first year after outplanting and to increased second-year stem unit elongation. The two shoot morphology differences indicate apparent variation in plant water relations, mineral nutrition or both during each of the two years of the study. Hole-planting did not influence growth and survival during the first year of the study. Contrary to previous reports, cold storage had a negative effect on January-lifted seedlings and did not affect November-lifted stock. The fundamental difference in shoot growth of the cold-stored stock was the number of stem units formed during year one in the resting terminal bud. If early dormancy induction in the nursery preceded earlier fulfillment of the chilling requirement and meristeniatic activity, cold storage may have inhibited leaf initiation either directly or indirectly. Study #2 was designed to evaluate the effects of fall lateral root pruning (LRP) prior to outplanting on seedling growth, and to further test the importance of initial root configuration. The results of the 2 x 2 factorial experiment indicated that 1) fall lateral root pruning is neither debilitating nor beneficial and 2) hole-planting is more favorable to seedling growth than slit-planting. No differences in height increment were observed between LRP and unpruned seedlings during the first growing season in an outdoor soil box. However, dry weight at the conclusion of the study was 30% less, probably due to re-establishment of the high-cost fine root component removed on pruning. LRP seedlings did not extend roots perpendicular to the slit-planting plant as originally hypothesized. Hole-planted seedlings grew 3.5 cm more In height and their root systems occupied three times the volume of soil at the conclusion of the study. These differences may be expanded upon In the future because of increased numbers of lateral buds formed on the terminal leader of hole-planted stock.
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