Effect of Seedpiece Size on Performance of three Potato Varieties
K.A. Rykbost and J.Maxwell'
Introduction
A survey of 19 commercial cut seed lots
in 1994 and 1995 confirmed previous
subjective observations of poor quality control
in local potato seed cutting operations. Only
two of the seed lots surveyed had more than 60
percent of seedpieces in the desired range of 1.5
to 2.5 ounces. Five lots had over 50 percent of
seedpieces under 1.5 ounces. The average for
all lots was 37 percent of seedpieces, on a
number basis, less than 1.5 ounces. A study
was established at KES in 1994 to evaluate
response to seedpiece size under local
conditions. The preliminary 1994 study with
Russet Burbank was expanded in 1995 and
1996 to include Russet Norkotah and Century
Russet.
Procedures
Seed tubers of Russet Burbank, Russet
Norkotah, and Century Russet were
individually sized to 3, 5, 7, 9, and 11 ounces
(within 1/4 ounce). This allowed appropriate
size seed from four-cut pieces to plant four
replications of one-row plots with 3/4, 1-1/4, 13/4, 2-1/4, and 2-3/4 ounce seedpieces. Russet
Burbank plots were 30 hills at 12.0-inch seed
spacing. Russet Norkotah and Century Russet
plots were 42 hills at 8.7-inch seed spacing.
Eight (Russet Burbank) or 11 (Russet Norkotah
and Century Russet) tubers were used for each
plot with two
1 /
bud-end pieces discarded in each case. This
ensured uniform numbers of bud-end and stemend pieces in each plot. All seed lots were cut
and treated with Tops 5.0 fungicide on May 9
and stored at approximately 55 °F and 95
percent relative humidity until planting on May
24.
Potatoes were planted with a one-row,
assisted-feed planter in 32-inch rows. Plots
were arranged in a split-plot design with variety
as the main-plot and seedpiece size as the splitplot. All fertilizer (1,000 lb/acre 15-15-15) was
banded at planting. Cultural practices were as
described on page 41. Emergence data were
recorded on June 17, June 24, and July 1. Stem
counts were determined on 10 consecutive
plants in each plot on September 9. Vines were
desiccated with Diquat applied at 1.0 pint/acre
on September 6. Potatoes were harvested with
a one-row, digger-bagger on September 27. All
tubers from each plot were stored and graded
on October 21.
Economic interpretations of findings
were based on the following assumptions:
1. Seed costs, including cutting and treating $12/cwt;
2. 17,424 or 21,780 seedpieces/acre for 10- or
8-inch seed spacing in 36-inch rows;
3. Crop values: Bs and culls - $1.00/cwt; No.2s
- $3.00/cwt; No.ls 4-8 ounce - $5.00/cwt;
No.ls 8-12 ounce - $10.00/cwt; No.ls >12
ounce - $8.00/cwt.
Superintendent/Professor and Biological Sciences Research Technician III, respectively,
Klamath Experiment Station, Klamath Falls, OR.
Acknowledgments: Partial funding support was provided by the Oregon Potato Commission.
Klamath Experiment Station
65
Results and Discussion
As in 1995, Russet Burbank emerged
earlier than the other varieties (Table 1).
Russet Norkotah and Century Russet
emergence was delayed for small seedpieces.
In Russet Burbank and Century Russet, small
seedpieces resulted in smaller and less vigorous
plants. Russet Norkotah vines were less
vigorous in general and were in advanced
stages of senescence in early September, while
Russet Burbank and Century Russet remained
vigorous until vines were desiccated. Stem
numbers were similar to those observed in
1995. Large seedpieces produced significantly
more stems in each variety. Seedpiece size did
not affect specific gravity.
There was a significant interaction
between variety and seedpiece size only for
yield of 4- to 8-ounce No.ls in 1996. There
were; however, different effects of seedpiece
size among varieties. Century Russet produced
relatively small increases in total No.1 yield for
each incremental increase in seed size (Table
2). In contrast, Russet Burbank experienced a
large yield increase from 3/4 to 1-1/4 ounce,
but no further benefit from larger seed size.
Seed size did not significantly affect total No.1
yield in Russet Norkotah. Effects of tuber size
were more pronounced and more consistent
among varieties. Larger seedpieces resulted in
reduced yields of large No.ls and increased
yields of Bs and small No.ls. The yield of Bs
produced from 2-3/4-ounce seedpieces was
more than double the yields of Bs produced by
3/4-ounce seedpieces, in all varieties. Yield
responses over three years for Russet Burbank
and two years for Russet Norkotah and Century
Russet are summarized in Table 3. Response
trends are similar to those observed in 1996 for
all varieties.
Gross crop values were calculated for
each plot individually using the prices listed for
various yield components. The highest gross
6 6
returns in 1996 occurred for 1-1/4, 1-3/4, and 23/4 ounce seedpiece size for Russet Burbank,
Russet Norkotah, and Century Russet,
respectively (Table 4). When seed costs are
considered, the economically optimum
seedpiece sizes in 1996 were 1-3/4 ounces for
all three varieties. When findings are averaged
over years, economically optimum seedpiece
sizes are 1-3/4, 1-1/4, and 2-1/4 ounces for
Russet Burbank, Russet Norkotah, and Century
Russet, respectively.
Effects of seedpiece size on
performance of Russet Burbank and Century
Russet are in general agreement with findings
from research in other production areas. Larger
seed resulted in earlier emergence, more
stems/plant, more tubers/plant, increased yields,
but a higher proportion of smaller tubers.
Economic effects vary depending on prices
assumed for components of yield and seed.
The prices used in this analysis result in
average returns of about $6.25/cwt on a total
crop basis. The average price declines as seed
size increases due to the higher proportion of
small, less valuable tubers. This is less than
returns for fresh market crops in good price
years, but higher than mean prices for the 19941996 crops.
Russet Norkotah response to seedpiece
size was similar to the other varieties in
emergence and stem numbers in both years.
Yields were not significantly affected by
seedpiece size in either year. The reasons for
this lack of response are not clear. Low
Norkotah yields in 1995 were thought to be the
result of early dying. The 1996 yields were
equal to Russet Burbank and do not indicate an
unusual condition in this variety. A third year
of evaluation for all three varieties in 1997 may
provide further insight in the discrepancy
between varieties.
Klamath Experiment Station
Table 1. Effect of seedpiece size on emergence, stem numbers, and specific gravity of Russet
Burbank, Russet Norkotah, and Century Russet potatoes grown at Klamath Falls,
OR, 1996.
Seed
size (oz.)
Variety
Emergence (%)
6/17
6/24
7/1
Stems/
plant
Specific
gravity
R. Burbank
3/4
1-1/4
1-3/4
2-1/4
2-3/4
91
94
100
98
99
98
100
100
100
100
100
100
100
100
100
2.1
2.5
2.6
3.2
3.5
1.086
1.085
1.082
1.083
1.084
R. Norkotah
3/4
1-1/4
1-3/4
2-1/4
2-3/4
50
67
67
64
77
89
97
93
88
98
95
99
97
96
99
2.3
2.4
2.6
3.3
3.4
1.070
1.069
1.069
1.072
1.067
Century R.
3/4
1-1/4
1-3/4
2-1/4
2-3/4
64
65
81
77
78
88
94
95
95
98
94
99
97
99
99
2.1
2.8
3.0
3.8
3.5
1.084
1.085
1.084
1.083
1.084
96
65
73
100
92
94
100
97
98
2.8
2.8
3
1.084
1.069
1.084
10
6
4
3
2
2
20
0.4
0.2
0.002
68
75
83
80
85
92
97
96
94
99
96
99
98
98
99
2.2
2.6
2.7
3.4
3.5
1.080
1.079
1.078
1.079
1.078
8
5
4
3
3
2
12
0.3
0.3
NS
Variety main effect:
R. Burbank
R. Norkotah
Century R.
CV (%)
LSD (0.05)
Seed size effect:
3/4
1-1/4
1-3/4
2-1/4
2-3/4
CV (%)
LSD (0.05)
Klamath Experiment Station
67
Table 2. Effect of seedpiece size on yield, grade, and tuber size distribution of Russet Burbank, Russet
Norkotah, and Century Russet grown at Klamath Falls, OR, 1996.
Seed
size
Variety
OZ.
Yield U.S. No. is
4-8 oz. 8-12 oz >12 oz. Total
Bs
Yield
No.2s
Culls
Total
cwtlA
R. Burbank
3/4
1-1/4
1-3/4
2-1/4
2-3/4
108
193
187
207
199
97
118
113
111
99
50
60
39
34
28
255
371
339
352
326
45
52
66
84
104
33
30
27
36
17
28
1
5
8
15
360
454
437
480
461
R. Norkotah
3/4
1-1/4
1-3/4
2-1/4
2-3/4
126
147
172
190
175
119
131
136
106
133
77
77
64
42
61
322
355
371
338
369
27
40
55
65
72
11
7
12
12
14
18
13
6
7
2
377
414
444
421
457
Century R.
3/4
1-1/4
1-3/4
2-1/4
2-3/4
191
217
261
272
322
113
130
141
135
123
76
62
44
50
41
379
408
445
456
486
33
57
73
73
113
8
8
5
11
5
18
13
5
9
7
438
486
528
549
611
179
162
252
108
125
128
42
64
54
328
351
435
70
52
70
28
11
7
11
9
10
438
423
522
CV (%)
LSD (0.05)
18
28
13
14
29
12
10
29
26
13
24
3
127
NS
9
31
3/4
1-1/4
1-3/4
2-1/4
2-3/4
141
186
207
223
232
109
126
130
117
118
68
66
49
42
43
319
378
385
382
394
35
50
65
74
96
17
15
15
19
12
21
9
6
8
8
392
451
470
483
510
CV (%)
LSD (0.05)
13
21
22
NS
53
23
12
38
26
14
35
5
102
9
10
37
Variety main effect:
R. Burbank
R. Norkotah
Century R.
Seed size effect:
68
Klamath Experiment Station
Table 3. Mean effect of seedpiece size on yield, grade, and tuber size distribution over three years
for Russet Burbank, and two years for Russet Norkotah and Century Russet potatoes
grown at Klamath Falls, OR, 1994 - 1996.
Variety
Seed
size
Yield U.S. No. is
4-8 oz. 8-12 oz >12 oz. Total
Bs
Yield
No.2s
Culls
Total
wt/A
O Z.
R. Burbank
Three year mean (1994 1996)
-
3/4
1-1/4
1-3/4
2-1/4
2-3/4
110
166
171
196
210
105
127
138
121
115
R. Norkotah
-
55
62
63
67
34
269
355
371
383
358
32
41
52
64
75
25
27
27
35
27
24
11
6
12
25
349
434
456
493
485
7
9
9
10
9
14
12
10
13
3
316
351
360
363
378
9
6
5
8
8
13
9
12
9
10
412
508
552
604
647
Two-year mean (1995 - 1996)
3/4
1-1/4
1-3/4
2-1/4
2-3/4
103
125
139
144
144
108
112
105
106
114
Century R.
63
55
49
44
51
272
290
292
292
308
24
41
50
50
58
Two-year mean (1995 - 1996)
3/4
1-1/4
1-3/4
2-1/4
2-3/4
128
165
211
218
281
128
180
186
206
178
108
97
80
104
84
26
52
58
59
86
364
442
477
528
543
Klamath Experiment Station
69
Table 4. Effect of seedpiece size on gross crop value, seed costs, and gross value less seed cost for Russet Burbank, Russet Norkotah,
and Century Russet potatoes grown at Klamath Falls, OR, 1994 - 1996.
Variety
Seed
size
1994
Gross Value
1995
1996
Mean
Seed
cost
/acre
oz.
gpo
tri
qix0
Pb
P.
op
a
6'
=
R. Burbank
3/4
1-1/4
1-3/4
2-1/4
2-3/4
R. Norkotah
3/4
1-1/4
1-3/4
2-1/4
2-3/4
Century
LSD (0.05)
Gross value less seed cost
1994
1995
1996
Mean
2490
3170
3460
3010
3160
—
-
1960
2240
2620
3070
2400
2080
2770
2530
2570
2370
2180
2730
2870
2880
2640
120
200
280
350
430
2370
2970
3180
2660
2730
1840
2040
2340
2720
1970
1960
2570
2250
2220
1940
2060
2530
2590
2530
2210
1770
1760
1610
1960
1880
2510
2730
2820
2450
2810
2140
2250
2220
2210
2350
150
250
340
440
540
-
-
1620
1510
1270
1520
1340
2360
2480
2480
2010
2270
1990
2000
1880
1770
1810
2760
2960
3160
3210
3300
2850
3480
3610
4080
3970
150
250
340
440
540
2790
3740
3710
4500
4090
2610
2710
2820
2770
2760
2700
3230
3270
3640
3430
310
3/4
1-1/4
1-3/4
2-1/4
2-3/4
-
2940
3990
4050
4940
4630
(Size)
580
340
-
-
-