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Sugarbeet Response to Nitrogen Fertilizer Rates
K.A. Rykbost and R.L. Dove1 1
INTRODUCTION
Fertilizer requirements for sugarbeets grown on low organic matter mineral
soils in the Klamath Basin have not been established. Research in other areas has
shown important relationships between nitrogen supplied and beet sugar content.
High nitrogen content in petioles late in the season has been related to reduced
sugar content and lower sugar extraction efficiency. The high efficiency of sugarbeet
roots in scavenging nitrogen from considerable soil depths may reduce fertilizer
nitrogen requirements compared to shallow-rooted crops such as cereals and
potatoes. This study was established to evaluate effects of a range of applied
nitrogen rates on sugarbeet petiole nitrate levels, yield, and sugar content.
PROCEDURES
The experimental site was a Hosley sandy loam soil. Previous crops were spring
barley from 1989 to 1991. The experimental design was a randomized complete
block with four replications. N fertilizer rates evaluated were 30, 60, 90, 120, and
150 lb N/A. Individual plots were four 22-inch rows, 20 feet long.
The field was fumigated with Telone II , shanked in at 20 gpa on November 15,
1991. Spring tillage included plowing on April 2, and disking on April 20, after a
broadcast application of 1.0 ton/A of agricultural gypsum. A uniform application of
188 lb/A of 16-16-16 fertilizer was supplemented with urea applied at appropriate
rates to individual plots to achieve planned N rates. Fertilizer was immediately
incorporated by harrowing on May 4. The seedbed was firmly packed with a
Brillion roller.
Monohikari seed was planted 0.5 inches deep at 8 seeds/foot with a PlanetJunior type planter on May 4. Cultural practices were the same as those described
for ICES variety trials (page 55). Stands were hand thinned to achieve in-row
spacings of 8 inches on June 3. No additional fertilizer was applied. A total of
approximately 22 inches of irrigation water was applied through solid-set sprinklers
on a twice weekly schedule.
1
/ Superintendent/Associate Professor and Assistant Professor, respectively,
Klamath Experiment Station, Klamath Falls, OR.
Acknowledgment: Partial funding of the study by the California Beet Grower's
Association and laboratory analyses of beet sugar content by the Holly Sugar
Corporation are gratefully recognized.
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Before fertilizer was applied, composite soil samples were collected from depths
of 1, 2, and 3 feet. Samples were analyzed at the University of California, Davis.
Beet petioles were collected from the two center rows of each plot on July 14 and
August 27. Samples were dried at KES and analyses were performed at the
Southern Oregon Analytical Laboratory at Tulelake, CA.
Beet tops were removed with a flail chopper immediately before harvest. Beets
were hand-harvested from 15 feet of the two center rows of each plot on October 9.
All beets from both rows were weighed and counted. All beets from one row were
analyzed for percent sucrose by Holly Sugar Corporation. Gross crop values were
calculated as described for variety experiments (page 55).
RESULTS AND DISCUSSION
Plant stands after thinning were quite uniform at populations of about 35,000
plants/A. The crop remained healthy throughout the season. There were no visual
differences in canopy development between plants over the range of fertilizer
treatments evaluated. Soil analyses showed uniform texture for all depths sampled:
89 percent sand; 6 percent silt; and 5 percent clay. Organic matter contents were
0.93, 0.17, and 0.10 percent for depths of 1, 2, and 3 feet, respectively. Soil pH
increased with depth from 7.6 in the top foot, to 8.0 in the second foot, and 8.4 in
the third foot. Soil cation exchange capacity (CEC) was uniform with depth at
about 13 meq/100g.
Soil N determinations included nitrate and ammonium-N for each foot and
mineralizable-N in the top foot. Nitrate-N concentrations were 7.83, 0.58, and 0.29
ppm at depths of 1, 2, and 3 feet, respectively. Corresponding ammonium-N was
1.16, 2.02, and 0.59 ppm, and mineralizable-N was 8.08 ppm in the top foot. This
represented total soil nitrogen reserves of about 85 lb N/A.
Petiole nitrate-N concentrations did not correlate well with fertilizer rates at
either sampling date (Table 1). Variability between replicates was high and differences between treatments were not statistically significant. The range of concentrations observed at both sampling dates was considered within sufficiency limits for
sugarbeets at that stage of development.
Effects of N-rate on yield, sugar content, sugar production, and gross crop value
were small and non-significant. Yield and sugar content increased slightly as N-rate
increased from 30 to 120 lb N/A. The highest N-rate did not reduce sugar content.
At current prices for nitrogen fertilizer, the economically optimum rate in this study
was 120 lb N/A. However, results suggest that high yields and sugar content are
attainable with low fertilizer inputs. Under climatic conditions experienced in the
Klamath Basin, nitrogen status of plants may not be as critical for sugar production
as it is in long growing season areas with higher fall temperatures. Local crops
grown in soils with 10 percent organic matter and high mineralizable-N have
attained over 19 percent sugar content in each of the last three seasons. Additional
research is needed to further define fertilizer requirements under local conditions
for major soil types.
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Table 1.
Effects of fertilizer N-rates on petiole nitrate-N levels, beet yields, sugar
content, sugar yield, and gross crop value for Monohikari grown at Klamth
Falls, OR. 1992.
N
Rate
lb N/A
30
60
90
120
150
Mean
CV (%)
LSD (0.05)
Petiole Nitrate-N
August 27
July 14
ppm Beet
yield
Sugar
content
Sugar
yield
Gross
value
T/A
32.4
%
19.2
19.2
19.4
T/A
6.22
6.46
6.51
$/A
1649
19.4
19.5
6.71
6.52
1776
1720
19.5
2
NS
6.48
6
NS
1715
6
NS
11,470
2,620
15,200
16,720
14,350
13,260
3,575
3,235
1,430
1,590
33.6
33.6
34.6
33.6
14,200
45
NS
2,490
82
NS
33.6
6
NS
1709
1724