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Nitrogen Response of Wheat, Corn and
Sunflowers in a Dryland Rotation Row Spacing Effect
M.F. Vigil, J.G. Benjamin, J. Schepers
PROBLEM: The current demand for edible oils has improved
the profitability of sunflowers in the Central Great Plains. However, knowledge
of sunflower response to fertilizer N in the region is limited. The objectives
here are: (i) to measure sunflower N response in a no-till
wheat-corn-sunflower-fallow rotation, (ii) to determine N fertilizer recovery of
this crop as affected by fertilizer placement method, and (iii) to compare
narrow row (20") production with conventional spacing.
APPROACH: Sunflower is planted and fertilized in a
split-plot 4-rep experiment. Main plots consist of rotation crop/phase
(sunflowers, corn, wheat or fallow). Sub-plots are fertilizer N rates of 0, 30,
60, or 90 lb N/acre. Sunflowers are planted in either 20 or 30 inch rows.
A seeding rate of 16,600 seeds per acre is used for both row spacings. In the 20
inch row plots, 2 rows are sprayed at the 5th leaf stage and at the early-bud
stage with zinc, copper, manganese and boron. Individual plots are 60 ft by 240
ft in size. Surface and deep placed 15N labeled fertilizer is used to
evaluate fertilizer N recovery with soil depth and N placement method.
RESULTS: In 2002 no corn or sunflowers were harvested due
to drought. We summarized the N rate effects on sunflowers and found that
Sunflowers need about 6-7 lbs of N per 100 lbs of grain production. Sunflower
grain yields have averaged around 1000 lbs/acre. Only one year out of 7 have we
measured a sunflower grain yield response to added N fertilizer (1999). In 2001,
a small increase in grain yield to added N was measured in corn. Wheat has
always, responded well to added N. We measured 60 bushel wheat at the 60 and 90
lb N rates with Trego white wheat. No significant yield response due to row
spacing was measured. In this study we have had 2 years in which row spacing has
not had an effect on yield and one year that it has. In all years, there is a
suppression of weed growth that is visually noticeable in the narrower rows. In
2000, a dryer than normal summer with low preplant soil water contents, we
measured less than 300 lbs of grain in our best sunflower plots. No row spacing,
N rate, or micronutrient responses were detected in 2000 with either sunflowers
or corn. Water was more limiting than these other management factors.
FUTURE PLANS: The experiment will be continued for
another 4 years to evaluate long term effects of intensive wheat-corn-sunflower
fallow rotations and to continue to evaluate N and row spacing effects on yield.
We are considering splitting the plots between soybeans and sunflowers, but
can’t do that until we have finished evaluating the row spacing effect for at
least 2 more years. The authors may be reached via e-mail
at: M.F. Vigil or
J.G. Benjamin
or phone: 970-345-2259. |