Abstract:
Three rates of urea, urea-DCD, and NH₄N0₃ were soil
applied in April and August 1986 to strawberry selection
OR-US 4930 and cultivar 'Sumas' to determine effects of the
nitrification inhibitor dicyandiamide (DCD) and nitrogen
source and rate on soil NH₄ and N0₃ levels, fruit yield and
quality, and mineral composition of foliage and fruit.
There were four replications of zero nitrogen plots.
For both OR-US 4930 and 'Sumas', soil NH₄ levels
reflected the seasonal mineralization pattern rather than a
fertilizer source or rate pattern. After the August
nitrogen treatments soil N0₃ was lower with urea-DCD than
with urea.
Urea-DCD altered mineral uptake by the plant, but did
not affect total marketable yield or quality of OR-US 4930
or 'Sumas'.
Petiole NO3-N was significantly (p < .05) increased by
increasing N rate in "Sumas' in March 1987.
Petiole N0₃-N of 'Sumas' and OR-US 4930 in June 1986
was significantly (p < .05) affected by an interaction of N
rate and source. OR-US 4930 petiole N0₃-N at the middle N
rate of urea was greater than at the same rate of urea-DCD.
At the high N rate there were significant differences among
all three sources. 'Sumas' petiole N0₃-N at the high N
rate of urea was greater than the same rate of NH₄N0₃.
OR-US 4930 leaf N content in August 1986 and fruit N
content in 1987 were significantly (p < .05) increased by
increasing nitrogen. 'Sumas' leaf N content in June and
November 1986 and in March 1987, fruit N content and
petiole N0₃-N in March 1987 were significantly (p < .05)
increased by increasing N rate.
Leaf N content of OR-US 4930 in June 1986 was
significantly (p < .05) greater with urea than with urea-
DCD. Fruit N content was significantly (p < .05) lower
with urea-DCD than with NH₄N0₃.
Leaf N content of OR-US 4930 in November 1986 was
significantly (p < .05) increased by increasing N applied
as NH₄N0₃ or urea-DCD.
Fruit S content of OR-US 4930 significantly (p < .05)
increased with increasing N. 'Sumas' leaf Ca content in
June 1986 and leaf P content in March 1987 significantly
(p < .05) decreased with increasing N.
Leaf K content of OR-US 4930 in June 1986 was
significantly (p < .05) greater with NH₄N0₃ than with urea-
DCD. Fruit P content was significantly (p < .05) greater
with urea-DCD and NH₄N0₃ than with urea. Leaf Cu content
in April 1987 was significantly (p < .05) lower with urea
than with NH₄N0₃. Leaf Mn content of 'Sumas' in June 1986
was significantly (p < .05) lower with urea versus urea-DCD
and NH₄N0₃.
Leaf P content of OR-US 4930 in April 1987 was
significantly (p < .05) greater at the low N rate of urea-
DCD than at the low N rate of NH₄N0₃ and the middle N rate
of urea. Leaf S content of OR-US 4930 in April 1987 was
significantly (p < .05) decreased by the low N rate of
NH₄N0₃.
Application of urea-DCD altered mineral uptake, in
June reduced petiole N0₃-N levels, and in August reduced
soil N0₃ levels, suggesting that the soil NH₄ to N0₃ ratio
was changed.
