Abstract:
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.
