Graduate Thesis Or Dissertation
 

Effects of tillage-induced soil compaction on carrot seedlings emergence and yield

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  • The effects of five tillage treatments on soil bulk density and mechanical impedance were examined on Newburg sandy loam soil in the Willamette Valley, Oregon, in 1987. Subsequent effects on seedling emergence and yield of carrots (Daucus carota L., cvs. Orlando Gold and Royal Chantenay) were also measured. Mechanical impedance was recorded on three dates at 2.5-cm intervals to a depth of 44 cm with a hydraulically driven penetrometer. A tillage pan often prevented penetration of the penetrometer beyond 35 cm. Soil cores were collected, on the days of penetrometer measurements, at three depths to measure bulk density and water content. Early season mechanical impedance at soil depths less than 23 cm was less in reduced tillage treatments than in conventional or excessive tillage treatments. Subsoiling before tillage resulted in less mechanical impedance at depths between 23 and 35 cm. Differences in mechanical impedance between treatments diminished later in the season to the point of being nonsignificant. Because of soil variability and the limited number of soil cores taken, bulk density differences between treatments were not significant for any of the dates. In both carrot cultivars, total yields were not significantly affected by tillage. Size distribution of roots (by diameter) was affected, with reduced tillage producing smaller diameter carrots. This was most likely a result of the slightly higher, though nonsignificant, number of seedlings emerged in the reduced tillage treatment. Seedling emergence of both cultivars had a moderate negative correlation with soil mechanical impedance at 5 cm.
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