82
Effects of N,P,K and S rates on Nutrient Status
and Crop Performance of Russet Burbank
K.A. Rykbost', N.W. Christensen' and J. Maxwells
INTRODUCTION
Potato production practices have changed significantly during the
past two decades in the Klamath Basin. Yield and quality improvements
have been achieved through more efficient irrigation management, higher
quality seed, better disease and pest control, and progress in potato
handling technology. Changes in crop rotation, increased use of soil
fumigants, improved tillage practices, acidification of mineral soils
and modifications in fertilizer practices have altered soil fertility
status and crop nutritional needs, and may require changes in fertilizer
practices.
Optimum utilization of fertilizers, soil amendments, agricultural
chemicals and other inputs is increasingly critical, not only to attain
economic viability, but to minimize impacts of agricultural activities
on soil and water resources. This study was initiated in 1988 to evaluate the effects of a range of N, P, K and S rates on the nutritional
status and performance of Russet Burbank potatoes grown on mineral soils
in the Klamath Basin.
PROCEDURES
Russet Burbank potatoes were planted in Poe fine sandy loam at 12inch seed spacing in 32-inch rows on May 25. Twelve pre-mixed fertilizer blends were spanked in on both sides of rows with a continuous
belt applicator on June 1. Treatments were arranged in a randomized
complete block design with four replications. Individual plots were
four rows, 40 feet long. Standard cultural practices were followed.
1/ Superintendent/Associate Professor, Biological Sciences Research
Technician, respectively, Klamath Experiment Station
2/ Professor, Department of Soil Science, OSU
Acknowledgments: Partial funding by the Potash and Phosphate Institute,
Oregon Potato Commission and Cooperative State Research Service (USDA)
is gratefully recognized.
83
Vines were desiccated with diquat applied at 2.0 pints/A with a
conventional ground sprayer on September 21. Tubers were harvested on
October 9. Harvest areas included the two center rows, trimmed to 37foot length. Total weights were determined in the field. Approximately
120-pound samples were stored and graded in early November.
Crop values were estimated based on December 1989 net price to
growers for each size and grade component of total yield, for fresh
market crops in the Klamath Basin. Prices were: 4-6 oz. No.l's $6.00/cwt; 6-10 oz. No. l's - $11.00/cwt; >10 oz. No. l's - $16.00/
cwt; B's and culls - $3.00/cwt; No. 2's - $4.50/cwt. These prices
doubled by late spring of 1990.
RESULTS AND DISCUSSION
Soil test sampling prior to planting indicated very high soil P and
K levels, low to medium S and Ca, a soil pH of 6.4 and very low organic
matter content (0.5 percent). The Poe soil is quite typical of potato
production soils in the area.
Growing conditions were more favorable in 1989 than the hot and dry
season experienced in 1988. June was warmer, promoting good early
season vigor. July and August were near normal in temperature. Crops
were not subjected to heat stress as in the 1988 season. No damaging
frosts were experienced until after vine desiccation. Under these conditions crop development was normal with yields and size being better
than average for Klamath Basin mineral soils.
Petiole samples were obtained from each plot on August 23 and September 7. Earlier sampling dates in 1988 failed to demonstrate differences between treatments in either P or K levels in petioles. In 1989
sampling was delayed until the plants at low nitrogen rates were well
into the senescence stage of development. By September 7, vegetative
growth had nearly ceased in plants receiving 60 or 120 lbs N/A. At the
highest N rate plants remained quite vigorous through early September.
Petiole levels of N were quite variable, but demonstrated N rate
responses at both sampling dates (Table 1). Petiole P levels were
clearly influenced by P application rates at both sampling dates.
Potassium levels were well within sufficiency ranges and did not
respond to K application rates. Petiole S levels were similar for the
two levels of S evaluated. An application of 1000 lbs/A of agricultural
gypsum in the spring of 1989 may account for a lack of S response in
petioles.
Yields of US No. l's averaged approximately 50 cwt/A higher than
yields experienced in 1988, with a higher percentage of larger tubers.
The percentage and yield of No. 2's and culls was also higher in 1989, a
typical response for Russet Burbank. A linear response to N rate was
observed in both total yield of No. l's and tuber size (Table 2). Each
additional increment of N increased tuber size and yield. In contrast
the maximum yield occurred at 180 lbs N/A in 1988.
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Optimum yields occurred at 60 lbs P 2 0 5/A both years (Table 3). It
is interesting to note that yields declined with the intermediate rates
but increased at the highest P rate in both years.
The potassium response in 1989 showed a clear trend for increased
yield of No. l's at higher K rates. This was not observed in 1988. In
both years slightly higher yields were obtained when sulfur was added to
the fertilizer blend at 40 lbs S/A.
One change in treatment design was incorporated in the 1989 experiment as a result of 1988 nutrient response. The 1988 data suggested
optimum treatment of 180-60-60. This combination with 20 lbs S/A was
evaluated in 1989, and resulted in the highest yield of No. l's and
total yield (Table 2).
Specific gravity response to nutrient levels was nearly identical to
results observed in 1988 (Table 2). Increasing N and K rates reduced
specific gravity. A slight increase was observed for high phosphorous
rates and when potassium sulfate was substituted for potassium chloride.
All of these relationships are consistent with experience elsewhere. In
both years specific gravity for all treatments was within an acceptable
range for processing crops.
Internal tuber quality was generally excellent. From a total of 480
tubers inspected, disorders observed included: hollow heart - 15; brown
center - 28; black spot - 6; and stem end discoloration - 23. No treatment affects were apparent except that one-third of the hollow heart
occurred where N was applied at the lowest rate.
Diseases were minimal in foliage and tubers. At the two lowest N
rates plants exhibited moderate early dying and early blight infections. Foliage in all other treatments remained quite healthy and
vigorous until vine desiccation. Some rhizoctonia occurred at all
fertility levels and was responsible for tuber malformations in a
portion of the culls. Tuber rot detected at grading represented less
than one percent of total yield in all treatments except the highest N
rate treatment, where rot accounted for 1.5 percent of total yield.
An economic interpretation of results for both 1988 and 1989 is
presented (Table 3). Net price to growers for US No. l's was the same
in both years. The 1988 prices included $1.00/cwt for B's and culls and
$3.00/cwt for No. 2's. Fertilizer prices were assigned at $0.30/lb for
N, $0.25/lb for P 2 0, and K 2 0, and $0.10/lb for S. The economically
optimum treatments were the combinations of 180-60-120 in 1988 and 18060-60-20 in 1989. The fresh market potato prices received in 1988 and
1989 are very high in relation to long term averages. Economic interpretations of the experimental findings should be tempered by recognition of this fact.
85
CONCLUSIONS
Efficient use of plant nutrients is important to growers for
economical reasons. It is becoming increasingly important in relation
to environmental considerations. The Klamath Basin's irrigation and
drainage system is closely entwined with two lakes and three wildlife
refuges which support a large and diverse population of native and
migratory birds. Algae and aquatic weeds are becoming increasingly
problematic in the basin's surface waters. At least one study has
detected groundwater nitrate-N levels in excess of federal drinking
water standards in several domestic wells. Nutrient contents in surface
waters are undoubtedly influenced by agricultural practices. The source
of nitrates in groundwater has not been determined to date; however,
agriculture has been implicated as a likely contributor.
Judicious use of agricultural chemicals, including fertilizers, will
be imperative in the future. Data derived over two years in this study
indicate that potato crops could be grown economically with substantially less P and K fertilizer than is traditionally used in Klamath Basin
crops. The study will be continued in 1990.
86
Table 1. Effects of N, P, K and. S rates on petiole nutrient levels in
Russet Burbank, 1989.
N
August 23 samples
K
PO4-P
N05-N
Fertilizer rate
S
K20
P205
lb/A
September 7 samples
N05-N
PO4-P
K
%
N Response
60
120
120
120
120
180
120
240
120
120
120
120
0
0
0
0
0.02
0.26
0.69
1.10
0.19
0.19
0.27
0.21
10.82
10.42
11.45
11.63
0.09
0.25
0.28
0.81
0.14
0.13
0.14
0.12
8.82
9.26
9.52
10.15
P Response
60
180
120
180
180
180
180
240
120
120
120
120
0
0
0
0
0.93
0.69
0.81
0.46
0.12
0.27
0.28
0.36
11.32
11.45
10.08
11.27
0.46
0.28
0.51
0.25
0.07
0.14
0.20
0.28
9.72
9.52
8.99
9.80
K Response
120
180
120
180
180
120
120
180
0
60
120
180
0
0
0
0
0.73
0.37
0.69
0.89
0.19
0.14
0.27
0.15
10.26
9.58
11.45
11.30
0.52
0.38
0.28
0.68
0.12
0.10
0.14
0.08
9.15
8.09
9.52
9.57
S Response
120
180
180
120
60
180
120
120
60
0
40
20
0.69
0.69
0.62
0.27
0.21
0.19
11.45
10.63
11.40
0.28
0.53
0.33
0.14
0.10
0.07
9.52
9.45
9.52
40
0.36
53
0.16
44
0.27
65
0.12
15
NS
CV (%)
LSD(.05)
13
NS
87
Table 2. Effects of N, P, K and S rates on yield and grade of Russet Burbank, 1989.
Yield of U.S. No l's
4-6 OZ 6-10 OZ >10 OZ Total B'S
cwt/A
Fertilizer rate
N
P205 K20 S
lbs/A
Yield
No 2's Culls
Total
Specific
Gravity
N Response
60 120
120 120
180 120
240 120
120
120
120
120
0
0
0
0
151
145
137
133
149
140
159
164
43
71
76
98
343
356
372
395
96
80
84
71
35
43
32
48
41
67
36
60
515
546
524
574
1.087
1.084
1.081
1.081
P Response
60
180
180 120
180 180
180 240
120
120
120
120
0
0
0
0
150
137
133
141
151
159
146
148
98
76
73
101
399
372
352
390
68
84
67
80
57
32
43
26
41
36
72
50
565
524
534
546
1.081
1.081
1.082
1.084
K Response
0
180 120
60
180 120
120
180 120
180
180 120
0
0
0
0
134
157
137
142
159
145
159
162
59
75
76
89
351
377
372
393
78
82
84
81
44
37
32
36
50
29
36
53
524
526
524
563
1.084
1.085
1.081
1.080
S Response
180 120
120
180 120
120
60
60
180
0
40
20
137
157
169
159
162
182
76
70
77
372
389
428
84
86
83
32
27
26
36
32
52
524
535
589
1.081
1.084
1.084
146
14
29
156
14
32
77
38
43
379
9
47
80
22
25
38
40
22
48
42
27
545
7
55
1.083
0.150
0.003
Average
CV(%)
LSD(.05)
88
Table 3. Economic implications of fertilization rates on fresh
market Russet Burbanks in the Klamath Basin.
Fertilizer rate
N
P205 K20
S
lb/A Fertilizer
cost
Crop value
1988 1989
Crop value - Fert. cost
1988 1989 2-Year Avg.
$/A
N Response
60 120
120 120
180 120
240 120
120
120
120
120
0
0
0
0
78
96
114
132
2842
2883
3343
3180
3795
4164
4279
4754
2764
2787
3229
3048
3717
4068
4165
4622
3241
3428
3697
3835
P Response
60
180
180 120
180 180
180 240
120
120
120
120
0
0
0
0
99
114
129
144
3977
3343
2944
3532
4712
4279
4176
4593
3878
3229
2815
3388
4613
4165
4047
4449
4246
3697
3431
3919
K Response
0
180 120
180 120
60
180 120
120
180 120
180
180 120
240
0
0
0
0
0
84
99
114
129
144
3438
3711
3343
3376
3614
4065
4231
4279
4613
--
3354
3612
3229
3247
3470
3981
4132
4165
4484
--
3668
3872
3697
3866
S Response
180 120
120
120
180 120
60
60
180
0
40
20
114
118
86
3343
3415
--
4279
4317
4759
3229
3297
--
4165
4199
4673
3697
3748
12
557
11
672
---
CV (X)
LSD(.05)
--