Download Tuber yield, storability, and quality of Michigan cultivars in response

Amer J of Potato Res (2004) 81:347-357
347
Tuber Yield, Storability, and Quality of Michigan Cultivars in
Response to Nitrogen Management and Seedpiece Spacing
C h r i s M. Long, Sieg S. S n a p p * , D a v e S. D o u c h e s , a n d R i c h a r d W. C h a s e
Depm'tmentof Crop and Soil Sciences, MichiganState University,East Lansing,Michigan,48824
*Correspondingauthor: Tel: 517-355-5187;Fax: 517432-2242;Email: [email protected]
ABSTRACT
e x c e l l e n t s t o r a g e c h a r a c t e r i s t i c s for different N f e r t i l i t y
levels a n d seedpiece spacing c o m b i n a t i o n s . Overall, the
I n f o r m a t i o n is r e q u i r e d o n n i t r o g e n (N) fertih'ty
r e c o m m e n d e d N fertilizer level for m o d e r a t e l y long-
a n d s e e d p i e c e m a n a g e m e n t for n e w c u l t i v a r s a n d
d u r a t i o n p o t a t o cultivars i n Michigan (200 kg N ha -~)
a d v a n c e d b r e e d i n g lines. I n t e r a c t i o n s a m o n g s t N fertil-
a n d a n a r r o w seedpiece spacing optimized yield a n d
izer rate, genotype, a n d seedpiece spacing are complex,
t u b e r q u a l i t y p e r f o r m a n c e while c o n s e r v i n g N fertilizer.
a n d can affect t u b e r yield, quality, a n d s t o r a b i l i t y as well
as N fertilizer efficiency. A field s t u d y was c a r r i e d o u t in
2001 a n d 2002 a t MSU M o n t c a l m Research F a r m i n cent r a l Michigan. T u b e r yields a n d p o s t - h a r v e s t q u a l i t y
RESUMEN
Se r e q u i e r e de i n f o r m a c i 6 n s o b r e fertilizaci6n con
c h a r a c t e r i s t i c s were e v a l u a t e d for five p o t a t o g e n o t y p e s
n i t r 6 g e n o (N) y m a n e j o de s e m i l l a c o r t a d a p a r a culti-
(MSG227-2, MSEI92-8Rus, J a c q u e l i n e Lee, Liberator,
vares n u e v o s y lineas a v a n z a d a s de m e j o r a m i e n t o . Las
a n d S n o w d e n ) i n r e s p o n s e t o a factorial c o m b i n a t i o n o f
i n t e r a c c i o n e s e n t r e la dosis de f e r t i l i z a n t e n i t r o g e n a d o ,
t h r e e N levels (200 kg N h a -~, 300 kg N ha -1, a n d 400 kg
g e n o t i p o y e s p a c i a m i e n t o de la semilla c o r t a d a s o n com-
N ha -~) and two seedpiece spacings, n a r r o w (0.20 m or
plejas y p u e d e n t e n e t impacto s o b r e el r e n d i m i e n t o , cal-
0.25 m ) a n d wide (0.33 m o r 0.38 m). N a r r o w seedpiece
idad y a l m a c e n a m i e n t o del tub~rculo, lo mismo que
spacing c o n s i s t e n t l y p r o d u c e d the highest U.S. No. 1
s o b r e la eficiencia del f e r t i l i z a n t e n i t r o g e n a d o . E n la
yields i n all g e n o t y p e s t e s t e d (37 a n d 34 t ha -t, n a r r o w vs
g r a n j a e x p e r i m e n t a l MSU Montcalm, Michigan c e n t r a l
wide spacing, respectively). There was a t r a d e o f f b e t w e e n
se hizo u n e s t u d i o de campo e n los afios 2001 y 2002. Se
seedpiece spacing a n d N level i n 2001 as t u b e r yields
evalu6 el r e n d i m i e n t o y la calidad de post-cosecha de los
were e n h a n c e d by higher N levels a t wide seedpiece
t u b ~ r c n i o s de cinco g e n o t i p o s de p a p a (MSG227-2,
spacing, b u t n o t a t n a r r o w spacing. I n 2002, t u b e r yield
MSE192-8Rus, J a c q u e l i n e Lee, L i b e r a t o r y S n o w d e n ) ,
was n o t enhanced, b u t p e t i o l e n i t r a t e - N a n d tuber-N
e n r e s p u e s t a a u n a c o m b i n a c i 6 n factorial de t r e s niveles
i n c r e a s e d as N f e r t i l i z a t i o n increased. G e n o t y p e was the
de N (200 kg N h a -1, 300 kg N h a -1 y 400 kg N ha -1) y dos
m a j o r factor t h a t i n f l u e n c e d t u b e r quality characteristics
e s p a c i a m i e n t o s p a r a semilla cortada, reducido (0.20m o
a t h a r v e s t a n d for stored t u b e r s (e.g., specific gravity,
0.25m) y largo (0.33m o 0.38m). E1 e s p a c i a m i e n t o
i n t e r n a l defects, bruising, chip color rating, sucrose, a n d
reducido de la semilla p r o d u j o c o n s i s t e n t e m e n t e los
glucose). Spacing had m i n i m a l effects, w h e r e a s higher
r e n d i m i e n t o s m~s altos de la US No. 1 con todos los
levels of N slightly r e d u c e d specific gravity b o t h years,
g e n o t i p o s p r o b a d o s (37 y 34 t h -~ con e s p a c i a m i e n t o
r e d u c e d i n t e r n a l defects i n 2001 a n d e n h a n c e d s u c r o s e
reducido v e r s u s largo r e s p e c t i v a m e n t e ) . Hubo diferen-
a t h a r v e s t in 2002. The cultivars t e s t e d d e m o n s t r a t e d
cias e n t r e el d i s t a n c i a m i e n t o de la semilla y el nivel de
Accepted for publication 25 May 2004.
ADDITIONAL KEY WORDS: Solanum tuberosum L., petiole nitrate,
Snowden, Jacquelme Lee, Liberator, MSG227-2,MSE192-8Rus
ABBREVIATIONS:MSU, Michigan State University; N, nitrogen; SFA,
Snack Food Association
348
AMERICAN JOURNAL OF POTATO RESEARCH
Vol. 81
N e n el 2001 a m e d i d a de que los r e n d i m i e n t o s se incre-
Tuber quality and storability over time are characteristics
m e n t a r o n debido a n i v e l e s altos de N e n los espaci-
that are becoming more important and must be considered for
a m i e n t o s largos de la s e m i l l a pero no en los de m e n o r
a wide range of cultivars, from tablestock to chip-processing
e s p a c i a m i e n t o . En el 2002, el r e n d i m i e n t o no se incre-
types. Quality traits common across genotypes include inter-
m e n t 6 pero el N-nitrato e n el p e c i o l o y el N e n el tub~r-
nal defects and bruising susceptibility (Baritelle et al. 2000). In
culo
addition, specific traits must be considered for different mar-
aumentaron
a medida que
se i n c r e m e n t 6
la
f e r t i l i z a c i 6 n nitrogenada. E1 g e n o t i p o f u e el factor m ~
i m p o r t a n t e que i n f l u y 6 sobre las caracteristicas
ket classes include after-cooking darkening in tablestock and
del
sugar profile, chip color, and other defects in processing culti-
t u b ~ r c u l o c o s e c h a d o y a l m a c e n a d o ( e s t o es, gravedad
vars (Sowokinos 2001). Genotype in large part determines
especlfica,
c o l o r de
tuber quality (Herman et al. 1996). Quality has been an impor-
hojuelas, c o n t e n i d o de sacarosa y glucosa). E1 distanci-
defectos
internos,
abolladuras,
tant selection criteria used by the Michigan potato-breeding
a m i e n t o t u v o e f e c t o s m l n i m o s , m i e n t r a s q u e los n i v e l e s
program in development of new cultivars (Douches et al.
a l t o s de N redujeron l i g e r a m e n t e la gravedad e s p e c i f i c a
2001a, 2001b).
e n a m b o s afios, asi c o m o los d e f e c t o s i n t e r n o s e n el 2001
Management can also influence tuber quality and interact
e i n c r e m e n t a r o n el n i v e l de sacarosa a la c o s e c h a e n el
with genotype. Nitrogen application rate did not have a con-
2002. Los cultivares p r o b a d o s m o s t r a r o n caracterlsticas
sistent effect on chip quality traits in a comparison of three
e x c e l e n t e s de a l m a c e n a m i e n t o con los d l f e r e n t e s n i v e l e s
processing cultivars (Herman et al. 1996). In the same study
de f e r t i l i z a c i 6 n n i t r o g e n a d a y las c o m b i n a c i o n e s de dis-
higher N rates were associated with tuber nitrate accumula-
t a n c i a m i e n t o de la s e m i l l a cortada. E1 n i v e l r e c o m e n -
tion and reduced specific gravity (Herman et al. 1996). A simi-
d a d o de f e r t i l i z a c i 6 n n i t r o g e n a d a ( 2 0 0 kg N ha -i) para
lar pattern of N rate and tuber nitrate accumulation was
cultivares de duraci6n m o d e r a d a m e n t e larga en Michigan
observed in a recent experiment (Belanger et al. 2002). Apply-
y un e s p a c i a m i e n t o r e d u c i d o de la semilla, f a v o r e c i e r o n
ing a larger portion of N fertilizer early in the growing season
el r e n d i m i e n t o y la calidad del tub~rculo m i e n t r a s se
was associated with higher bruising susceptibility in Russet
m a n t u v o la f e r t i l i z a c i 6 n con N.
Burbank tubers (BariteUe et al. 2000), and potato tuber starch
accumulation was reduced with increasing N and potassium
INTRODUCTION
inputs in another Russet Burbank study (Westermann et al.
1994). Interestingly, an increase in nitrate-N in tubers was
Optimizing nitrogen (N) management for each cultivar
associated with high sucrose levels and reduced chip color
and cropping system is critically important to tuber yield and
quality in a 6-month storage study (Kolbe et al. 1995). There is
quality (Joern and Vitosh 1995). Understanding interactions
lhnited data on direct links between excess N application and
amongst N fertilizer rate, genotype, and seed spacing allows
altered sugar profiles that compromise chip quality late in stor-
the development of appropriate N management strategies.
age. In-depth study of quality parameters and tuber ability to
Inadequate N can limit tuber size and marketable yield, allow
maintain color in response to N is required in long-term stor-
weeds to compete with the crop, and enhance plant suscepti-
age (Salazar and Busch 2001).
bility to the early die complex. Excess late summer N can delay
Potato genotypes vary markedly in response to N fertility.
tuber maturity, reduce effectiveness of vine-dessicants, and
Longer-season cultivars tend to require higher rates of N for
may adversely affect tuber quality and storability (Belanger et
maximum yields, but this does not hold in all cases (Arsenault
al. 2002). This last is critically important for chip-processing
et al. 2001; Lewis and Love 1994). Two tablestock cultivars and
cultivars, yet there is very little information on the interaction
two chip processing cultivars have recently been released
of N management, plant population density, and tuber quality.
from the Michigan program. The new cultivars Liberator
Seedpiece spacing and N fertilizer level frequently influence
(MSA091-1), a 10 C storage chipper with tolerance to common
both tuber set and size. For example, the ratio of Canada No. 1
scab (Streptomyces scabies Thaxter) (Douches et al. 2001a);
yields to total yield was increased by either enhanced N appli-
MSG227-2, a cold storage (7.2 C) chipper with common scab
cation or increasing spacing, for five out of eight cultivars
tolerance; MSE192-8Rus, a russet tablestock line with excel-
investigated in Prince Edward Island (Arsenault et al. 2001).
lent tuber internal quality; and Jacqueline Lee (MSG274-3), a
2004
LONG et al.: MICHIGAN CULTIVAR N RESPONSE
349
European-type tablestock line tolerant to the US 8 genotype of
The five lines evaluated were recently released cultivars or are
Phytophthora infestans (Douches et al. 2001b).
cultivars about to be released from the Michigan potato-breed-
The objectives of this study were (1) to determine the
ing program (D. Douches, pers comm 2001). Two of the lines
yield, quality and petiole nitrate-N response of four potato
are in the chip-processing market class, MSG227-2 and Libera-
genotypes (MSG227-2, MSE192-8Rus, Jacqueline Lee, Libera-
tor (Douches et al. 2001a), whereas the other two lines are
tor) and one standard cultivar (Snowden) to N fertility at mod-
tablestock, MSE192-8Rus and Jacqueline Lee (Douches et al.
erate, high and supra-optimum levels; (2) to evaluate the
2001b). Snowden is a widely grown chip-processing cultivar
interaction of line, seedpiece spacing and N fertility; and (3) to
that was included as a check (Love 1999).
determine if N status or cultivar influenced quality character-
Crop Management
istics during storage.
The research site is maintained in a bean-corn-potato
MATERIALS AND METHODS
rotation; field corn (Zea mays) and a rye (Secale cereale) winter cover crop was grown the year prior to initiating the exper-
Site description
iment in 2001 and in 2002. Fertilizer management followed
The study was carried out in 2001 and 2002 at the MSU
Michigan State University recommendations, including potas-
Montcalm Research Farm near Entrican, in central Michigan
sium at 217 kg ha -~ applied pre-plant, and phosphorus at 41 kg
The soil type at the research field
h ~ 1 applied at planting (Vitosh 1990). Before planting in late
site is an Alfic Fragiorthod Montcalm/McBride loamy sand to
April each year soils were sampled in 0.25-m increments to a
sandy loam with 77% to 84% sand, 11% to 19% silt and 4% to 8%
0.75-m depth using a 3-cm-diameter corer. A composite of
clay content, and 0.8% to 1.3% organic carbon in the top 20 cm
eight sub-smnples was randomly taken across each replicate
(lat. 43~
long. 85~
of soil (Snapp et al. 2003). The trial was conducted at adjacent
for the four replicate areas of the experimental site. Thus, a
sites in 2001 and 2002.
total of four composite samples per depth were collected and
stored in plastic bags at 4 C. Soil inorganic nitrate was extracted
Experimental Design
Five potato genotypes were evaluated for response to
with 1N KC1 and shaken at 180 rpm for 30 min before being
sieved through #1 Whatman filter paper (moistened frost with
three levels of nitrogen fertilizer (200, 300, and 400 kg N ha -1)
1N KC1 to remove possible nitrate contamination). Inorganic
and a narrow and a wide seedpiece spacing within row. Pre-
nitrate-N was determined in extracts by colormetric methods
liminary research indicated that spacing of 0.20 m (narrow)
using an autoanalyzer (Lachat Instrunmnts Inc., Milwaukee,
and 0.33 m (wide) was appropriate to test all of the lines
WI). In the top 25-cm depth, the soil nitrate-N was 6.3 ppm in
except Jacqueline Lee, which was expected to produce higher
2001 and 7.5 ppm, and less than 2.0 ppm in soil deeper in the
yields at a moderately wider seedpiece spacing (Douches et al.
profile. This is less than the 20 ppm nitrate soil threshold indi-
2001b). Thus a 0.25 m (narrow) was compared to 0.38 (wide)
cated in Michigan State University potato fertility recommen-
seedpiece spacing for Jacqueline Lee. Nitrogen levels were
dations, thus fertilizer nitrogen applied was not adjusted for
chosen to represent the moderate level (200 kg N ha -~) cur-
initial soil nitrogen (Snapp et al. 2002). Nitrogen fertilizer was
rently recommend for medium duration cultivars in Michigan
applied in four equal parts, at planting and as three split-appli-
(Vitosh 1990), a higher level (300 kg N h ~ 1) to test N yield
cations to achieve three rates (200, 300, and 400 kg N ha-l). The
response, and a supra-optimum level of 400 kg N h ~ ~ that is
three split-applications were applied at hilling (mid-June), in
applied by some growers in years, depending on the precipita-
early July, and in mid-July.
tion pattern (Snapp et al. 2001).
Seedpieces were cut as close to 57 g as possible and
The study was conducted using a randomized split-split
selected for uniformity before planting. Rows were opened
plot design with four replications. The main plot was nitrogen
using potato-planting equipment, and planted by hand to
fertilizer level, the sub-plot was potato line, and the sub-sub
achieve uniformity and precision in spacing seedpieces. Pest
plot was seedpiece spacing. Each plot was bordered on both
control followed recommended practices, applying imidaclo-
sides by a guard row for a total of three rows (0.86 m between-
prid, metribuzin, and metolachlor as required. On average, 845
row spacing) each 7.7 m long; total plot size was 2.6 m x 7.7 m.
base 10 C growing degree days (GDD) were recorded at the
350
AMERICAN JOURNAL OF POTATO RESEARCH
Vol. 81
experiment site for the two growing seasons. Conditions were
a check and 25 tubers for a tumbled sample to simulate bruise
slightly warmer in 2002 than 2001, but both seasons were close
potential in normal harvesting and storage operations. The
to the long-term average for the site. Total precipitation during
tumbled samples were placed in a cooler for 12 h at 10 C and
the growing season was 0.64 m in 2001 and 0.55 m in 2002, with
then placed in a hexagon plywood drum for 10 rotations to
an additional 0.14 m applied through the irrigation system in
simulate bruise. The check sample remained at room temper-
2001 and 0.18 m applied in 2002. Potatoes were planted on
ature. Blackspot bruise was allowed to develop 14 days before
2 May 2001 and vines desiccated with one application of diquat
both samples were abrasively peeled and assessed for the
at labeled rate on 30 August 2001; harvest was conducted 138
number of blackspot bruises on each potato (Douches et al.
days after planting on 17 September 2001. In 2002, planting
2001a). Average blackspot number per check tuber was sub-
was conducted on 29 April 2002, vine~ll on 11 September 2002
tracted from average blackspot per tumbled tuber, to deter-
with one application of diquat at labeled rate, and harvest 155
mine a blackspot bruise score.
days after planting on 30 September 2002.
Post-harvest Monitoring
Plant Monitoring
Post-harvest evaluations for after-cooking darkening
Stand counts per plot were measured 7 wk after planting
(ACD) were conducted for the two tablestock cultivars, and
to determine plant population density. An evaluation of plant
chip color was measured for the three chip-processing culti-
vigor was conducted using a visual rating on a 1-5 scale where
vars. Post-harvest evaluations were performed on a composite
1 = least vigorous and 5 = most vigorous (R. Chase, pets
sample of potatoes for each cultivar and N treatment across
comm). Petiole sampling for nitrate-N monitoring were col-
spacing treatments to monitor N-level by cultivar interactions.
lected 66, 79, 90, 99, and 111 days after planting in 2001 and 64,
As tubers harvested were insufficient to allow all interactions
78, 92, and 107 days after planting in 2002. Thirty randomly col-
to be monitored, four replicates for each N-level by cultivar
lected petioles were collected per plot, selecting among fourth
combination were monitored. Chip-processing quality was
fully expanded petioles per plant to improve uniformity (Lang
assessed on 25-tuber samples, taldng two longitudinal slices
et al. 1999). Petioles were immediately dried and ground to
from each tuber. Chips were fried at 185 C, and the color was
pass a 2-mm sieve. Nitrate-N in leaves was determined color-
evaluated visually and scored, using the snack food associa-
metrically by Techmark, Inc. (Lansing, MI).
tion 1-5 color chart (Douches et al. 2001a).
Tuber Yield a n d Quality Characteristics
samples of 40 tubers were assessed for chip quality character-
For each of the three chip-processing lines, three subThe central row of each plot was harvested and tubers
istics. Evaluation was conducted at harvest, after 3 months of
were sized and evaluated using a potato-grading line. Total
storage (in late January), and after 6 months of storage (in late
yield fresh weight was determined, as well as size distribution,
April). The tuber samples went into a commercial-type storage
as follows: oversize > 8.3 cm, U.S. No. 1 > 5.1 cm, B < 5.1 cm,
(Dr. B. F. Cargill Potato Demonstration Storage located adja-
and external defect tubers with external physiological defects.
cent to the MSU Montcalm Research Farm, Entrican, MI) at 14
Internal defects were evaluated by cutting 40 oversize tubers
C. After approximately 1 month the samples where cooled to
(-> 8.3 cm) per treatment longitudinallyand evaluating internal
12 C and maintained at this temperature with a relative humid-
quality. This involved monitoring for presence of stem end dis-
ity of 95% for the remainder of the storage season.
coloration, hollow heart, and internal necrosis from brown
Sucrose and glucose analysis, chip color and defects were
spot or brown center. Tubers were counted for each size class
analyzed at a commercial potato tuber analytical laboratory,
using a sub-sample that consisted of a random selection of
Techmark, Inc. (Lansing, MI). Sucrose and D-glucose were
about half the tubers harvested per plot. Specific gravity was
measured from fresh tuber core samples using the indnstry
determined using the weight-in-air/weight-in-watermethod for a
standard methodology directly in a macerated potato matrix
sub-sample of U.S. No. 1 tubers, weighing approximately 2000 g.
solution by an automatic analyzer based on enzyme technol-
To evaluate blackspot bruise potential, two 25-tuber sub-
ogy, a YSI2700 Select Biochemistry Analyzer (Yellow Springs
samples were collected from each plot harvested, 25 tubers for
Instrument, Inc., Yellow Springs, OH). In 2002 we dried half of
2004
LONG et al.: MICHIGAN CULTIVAR N RESPONSE
each of the tubers used above for chip quality analysis, ground
351
tubers were removed from the cooler cut in haft and one half
tissue to pass a 2-mm sieve, and analyzed for nitrate-N deter-
of each tuber was placed in a steaming tray. The ten halves
mined colormetrically by Techmark, Inc. (Lansing, MI).
were steamed until cooked, about 45 min. Once cooked the
The primary evaluation of tablestock quality was based
steamed tubers were allowed to cool 1 h on the countertop at
on the ability of a cultivar to not darken after cooking. The
room temperature, stored for 24 h at 4.4 C, and then evaluated.
after-cooking darkening (ACD) evaluation was preformed at
Russet Norkotah and Russet Burbank were used as controls.
three times, out of the field, late January, and late March on the
Russet Norkotah typically has an undesirable ACD dark color,
tablestock cultivars. The ACD samples consisted of 10 ran-
whereas Russet Burbank is white and serves as a positive con-
domly selected tubers from each line and nitrogen treatment
trol. The tubers were rated on a subjective 1-5 scale where 1 was
replication. These tubers were stored at 40 F after harvest. Ten
a white flesh color after cooking and 5 was a dark gray color.
F I G U R E 1.
Total tuber yield p r e s e n t e d for five cultivars - - including
a d v a n c e d b r e e d i n g l i n e s - - at Montcalm R e s e a r c h F a r m (Entrican, M I ) in 2001. S e e d p i e c e s p a c i n g w a s 0.20 m ( n a r r o w ) and
0.33 In ( w i d e ) , e x c e p t for t h e cultivar J a c q u e l i n e L e e w h i c h w a s
e v a l u a t e d at 0.25 m ( n a r r o w ) a n d 0.38 ( w i d e ) , b a s e d o n preliminary data. N-fertilizer r a t e s c o m p a r e d w e r e 2 0 0 kg N ha -a, 3 0 0
kg N ha -1, and 4 0 0 kg N ha-L
F I G U R E 2.
Total t u b e r yield p r e s e n t e d for five cultivars at the Montcalm
R e s e a r c h F a r m in 2002. Cultivars, s e e d p i e c e spacing and N-fertilizer r a t e s u s e d a r e as d e s c r i b e d in Figure 1 legend.
352
A M E R I C A N J O U R N A L O F POTATO R E S E A R C H
Statistical Analysis
Vol. 81
a d v a n c e d b r e e d i n g lines about to b e r e l e a s e d and r e l e a s e d cul-
Crop data w e r e analyzed using the MIXED p r o c e d u r e of
tivars. Markedly similar t r e n d s w e r e o b s e r v e d for total t u b e r
SAS after testing for h o m o g e n e i t y o f variance (SAS v. 8, SAS
yield in 2001 and 2002 (Figures 1 and 2). Ttle chip-processing
Inst., 2001). Yield of different sized class t u b e r s a n d t u b e r char-
cultivars (Snowden, Liberator, and MSG277-2) consistently
acteristics w e r e s u b j e c t e d to analysis o f variance (ANOVA) for
p r o d u c e d m o r e U.S. No. 1 t u b e r s and higher yields t h a n the
a r a n d o m i z e d c o m p l e t e b l o c k split-split-plot design with N
t a b l e s t o c k cultivars included in this s t u d y (Jacqueline Lee a n d
t r e a t m e n t as the main-plot factor, cultivar as t h e split-plot fac-
MSE192-8Rus). Overall, Liberator h a d t h e m o s t vigorous vine
tor, and spacing o f s e e d p i e c e as the split-split p l o t factor. Qual-
(data n o t s h o w n ) and was a c o n s i s t e n t l y high yielder (Tables 1
ity and biochemical characteristics of s t o r e d t u b e r s w e r e
and 2). This s u p p o r t s the r e c e n t r e l e a s e o f this cultivar, w h i c h
s u b j e c t e d to a t w o w a y ANOVA, with nitrogen fertilizer as the
also h a s significant resistance to c o m m o n scab ( D o u c h e s et al.
m a i n factor and cultivar as t h e split-plot factor.
2001a). A t r e n d t o w a r d s i n c o n s i s t e n t yield r e s p o n s e w a s
o b s e r v e d in line MSG227-2, as U.S. No. 1 t u b e r weight w a s 51.2
t h ~ 1 a n d 37.2 t h ~ ~in 2001 and 2002, respectively.
RESULTS A N D D I S C U S S I O N
The t a b l e s t o c k cultivar Jacqueline Lee w a s not low yield-
Cultivar Response
ing p e r se, b u t the p r o p o r t i o n o f B-sized (small) t u b e r s w a s
Caltivar w a s t h e p r i m a r y d e t e r m i n a n t o f t u b e r yield for
high a c r o s s all agronomic t r e a t m e n t s (14% c o m p a r e d to culti-
U.S. No. 1, B's, and t u b e r quality characteristics (Tables 1-3).
v a t average o f 5% in 2001; 7% c o m p a r e d to cultivar average o f
Note that w h e n r e f e r e n c e is m a d e to "cultivar," this includes
2% in 2002). The s a m e t r e n d s w e r e o b s e r v e d w h e t h e r t u b e r
n u m b e r (data not s h o w n )
or t u b e r weight (Tables 1
TABLE 1--Effect of nitrogen fertilizer rate applied, cultivar and spacing on yield and tuber
characteristics in 2001 at Montcalm Research Farm, Entrican, MI. Seedpiece
spacing was 0.20 m (narrow) and 0.33 m (wide), except f o r cultivar Jacqueline
Lee, which was evaluated at 0.25 m (narrow) and 0.38 m (wide).
U.S. No. 1~
(t hw')
N Fertilizer (kg ha 1)
200
300
400
Cultivar
Snowden
MSG227-2
Liberator
Jacqueline Lee
MSE192-8Rus
Spacing
Narrow
Wide
Source of Variation
N Fertilizer
Ctdtivar
N Fertilizer x Cultivar
Spacing
N Fertilizer x Spacing
Cultivar x Spacing
N x Cultivar x Spacing
B
(t ha-')
External
Defects
(t hw ~)
Specific
Gravity
Internal
Defects2
%
a n d 2) w e r e c o n s i d e r e d .
This t e n d e n c y to p r o d u c e
smaller tubers led t o low
U.S. No. 1 yields c o m p a r e d
to o t h e r genotypes tested,
although total t u b e r yield
w a s maintained in Jacque-
34.9b
37.6a
34.5b
1.8~
1.7h
1.9~
0.1b
0.1b
0.2~
1.072~
1.072~
1.071 b
16~
14~
9b
39.8b
51.2~
40. i b
25.0~
22.1r
1.4~
0.8b
0.8~
3.6~
2.3~
0.0b
0.1~
0.2~
0.2~
0.29
1.074 ~
1.0749
1.076~
1.072~
1.063b
25~
l0 b
23~
4~
4r
34.3~
32.5b
2.@
1.4b
0. i
0.1
1.072~
1.071b
13
13
***~
***
NS
**
***
**
NS
*
***
NS
***
NS
**
NS
**
***
NS
NS
NS
NS
NS
line Lee (Figure 1). A relatively high t u b e r s e t and
limited tuber bulking m a y
explain t h e large n u m b e r o f
B-sized tubers p r o d u c e d by
Jacqueline Lee ( D o u c h e s et
al. 2001b). For this cultivar,
w i d e p l a n i n g s p a c e at high
N fertilizer levels m o d e r ately r e d u c e d the p r o p o r -
***
***
tion o f B-sized t u b e r s in
*
*
NS
*
NS
NS
NS
NS
NS
NS
2001 f r o m 14.5% t o 11.3%,
~Size distribution: B < 5.1 cm, U.S.#1 _>5.1 cm, external defects = tubers with external defects.
2Internal defects, % of 40 oversize tubers > 8.3 cm that had internal defects (hollow heart, internal necrosis,
stem end discoloration).
3NS = not significant; * = p value < 0.05; ** = p value < 0.01; *** = p value < 0.001.
a n d in 2002 from 4.4% to
2.9%. It d o e s not a p p e a r that
it will be straight f o r w a r d to
use N m a n a g e m e n t or s e e d
spacing to e n h a n c e t u b e r
size in Jacqueline Lee.
2004
LONG e t
al.:
MICHIGAN CULTIVAR N R E S P O N S E
353
The p r o p o r t i o n o f externally defective t u b e r s w a s very
g e n o t y p e i n f l u e n c e d bruise rating in b o t h years. In 2001, bruise
low in S n o w d e n (Tables 1 and 2). This may b e one o f t h e fac-
ratings w e r e in the d e s c e n d i n g order: Jacqueline Lee < Snow-
t o r s that contribute to the continuing popularity of this chip-
d e n < Liberator < MSG227-2 < MSE192-8Rus (1.47, 0.68, 0.48,
p r o c e s s i n g cultivar. Tuber specific gravity in t h e t w o y e a r s the
0.27, and 0.12, respectively). The s a m e t w o lines had low sus-
e x p e r i m e n t w a s carried out w a s m o d e r a t e l y low, w h i c h is
ceptibility to bruising in 2002, in t h e following order: Liberator
reflected in the values r e p o r t e d h e r e (Tables 1 and 2). This is
< Jacqueline Lee < S n o w d e n < MSG227-2 < MSE192-8Rus
c o n s i s t e n t with o t h e r r e s e a r c h carried out at this site (Snapp
(1.28, 0.96, 0.59, 0.26, and 0.22, respectively). Liberator has
et al. 2003). Level o f internal defects varied with cnitivar
b e e n o b s e r v e d previously to have bruising susceptibility simi-
(Tables 1 and 2). They w e r e consistently low in Jacqueline Lee
lar to S n o w d e n ( D o u c h e s et al. 2001b).
(average = 4.6% in 2001 and 2.1% in 2002) and high in Liberator
Overall, the cultivars evaluated in this study d e m o n -
(average = 24.6% in 2001 a n d 24.6% in 2002) a n d S n o w d e n
s t r a t e d excellent storage c h a r a c t e r i s t i c s a c r o s s a range o f N
(average = 24.2% in 2001 a n d 14.2% in 2002). Internal d e f e c t s
fertility levels, and for wide vs n a r r o w s e e d p i e c e spacing. In
c o n s i s t e d primarily o f s t e m e n d discoloration in this study,
tablestock, g e n o t y p e altered t u b e r color r e s p o n s e to cooking.
a l t h o u g h h o l l o w h e a r t a n d i n t e r n a l n e c r o s i s w e r e also
Stored t u b e r s r e m a i n e d white after cooking in MSE192-8RUS
(ACD s c o r e o f 1.0), but t u r n e d dark after cooldng in Jacqueline
o b s e r v e d at very low incidence.
Tuber factors influencing p r o c e s s i n g quality w e r e moni-
Lee (ACD s c o r e o f 3.0). In c h i p - p r o c e s s i n g lines t h e r e w a s also
t o r e d at harvest for all cultivars (Table 3) and in post-harvest,
a significant cultivar effect on the quality, as indicated b y the
s t o r e d t u b e r s for c h i p - p r o c e s s i n g cultivars (Table 4). P o t a t o
sugar profile. Sucrose and glucose w e r e m o n i t o r e d o v e r time
in s t o r e d t u b e r s o f c h i p p r o c e s s i n g lines (Table 4).
TABLE 2--Effect of nitrogen fertilizer rate applied, cultivar and spacing on yield and
tuber characteristics in 2002 at Montcalm Researqh Farm, Entrican, MI.
Snowden
Seedpiece spacing was 0.20 m (narrow) and 0.33 m (wide), except for cultivar
Jacqueline Lee which was evaluated at 0.25 m (narrow) and 0.38 m (wide).
U.S. No. 11
(t ha-')
B
(t ha-')
External
Defects
(t ha-')
Specific
Gravity
sucrose
values
w e r e low after 3 m o n t h s stor-
Internal
Defects2
%
age, but w e r e highest after 6
m o n t h s o f storage (Table 4).
The o p p o s i t e p a t t e r n w a s
o b s e r v e d in Liberator, w h e r e
m o d e r a t e l y elevated s u c r o s e
N Fertilizer (kg ha-l)
200
300
400
Cultivar
Snowden
37.9a
36.1a
32.2b
0.7
0.7
0.7
0.4~'
0.5~b
0.6~
1.069a
1.068a~
1.06F~
10b
9b
13~
levels w e r e o b s e r v e d initially
37.8a
0.8b
0.1
1.070a
14~
Maintaining low sugar levels
MSG227-2
37.2 ~
0.3 ~
0.9
1.068 ~
8~
is n e c e s s a r y t o obtain desir-
Liberator
35.5 b
0.3"
0.4
1.073 ~
25 ~
35.2b
31.2c
1.3~
0.9~
0.7
0.5
1.070a
1.061b
2c
4c
34.3a
32.5b
2.@
1.4b
0.1
0.1
1.072
1.071
13
13
***3
**
***
**
NS
***
***
***
***
***
after 6 m o n t h s of storage for
*
NS
NS
*
NS
the
***
NS
***
NS
**
NS
**
NS
Jacqueline Lee
MSE 192-8Rus
Spacing
Narrow
Wide
Source of Variation
N Fertilizer
Cultivar
N Fertilizer x Cultivar
Spacing
N Fertilizer x Spacing
Cultivar x Spacing
N x Cultivar x Spacing
***
NS
**
NS
NS
NS
*
NS
NS
NS
NS
NS
~Size distribution: B < 5.1 cm, U.S. #1 _>5.1 cm, external defects = tubers with external defects.
~Internal defects, % of 40 oversize tubers > 8.3 cm that had internal defects (hollow heart, internal necrosis,
stem end discoloration).
~NS = not significant; * = p value < 0.05; ** = p value < 0.01; *** = p value < 0.001.
and final levels w e r e the lowest overall at 0.6 Bg m g -1-
able chipping quality. Chip
c o l o r as rated using a visual
SFA s c o r e w a s not influenced
b y cultivar. It r e m a i n e d n e a r
the optimal SFA rating of 1.0
three
chip-processing
lines t e s t e d (Table 4). This
was
consistent
with
the
e m p h a s i s o f t h e Michigan
potato-breeding p r o g r a m on
chip
quality
parameters
( D o u c h e s et al. 2001a).
354
AMERICAN
JOURNAL
OF POTATO
RESEARCH
Vol. 81
TABLE 3---Effect of N fertilizer level applied and cultivar on tuber quality characteristics at harvest f r o m field
experiments in 2001 and 2002 conducted at Montcalm Research Farm, Entrican, MI.
2001
N Fertilizer ( k g h x ~)
200
300
400
Cultivar
Snowden
MSG227-2
Liberator
Jacqueline Lee
MSE192-8Rus
Source of Variation
N Fertilizer
Cultivar
N Fertilizer x C u l t i v a r
2002
Bruise
Rating ~
(Spot/tuber)
Chip
Color2
(SFA)
Bruise
Rating
(Spot/tuber)
Chip
Color
(SFA)
Sucrose
2002
(pg/mg)
Glucose
2002
(~g/mg)
0.6
0.6
0.6
1.0
1.0
1.0
0.8
0.6
0.6
1.0
1.1
1.1
0.75 h
0.80 ~
0.81 ~
0.02
0.02
0.03
0.7 ~b
0.3 ~
0.5 b
1.5~
0.1 b~
1.0
1.0
1.0
NA
NA
0.6 b
0.3 b
1.3~
1.0 ~
0.2 ~
1.0
1.2
1.0
NA
NA
0.72 h
0.83 ~
0.8 ~
NA
NA
0.02
0.03
0.02
NA
NA
NS ~
**
NS
NS
NS
NS
NS
**
NS
NS
NS
NS
**
**
NS
NS
NS
NS
~Bruise r a t i n g = a v e r a g e n u m b e r o f b r u i s e d s p o t p e r t u b e r o n t t w a b l e d t u b e r s , s u b t r a c t i n g a v e r a g e s p o t p e r t u b e r in n o n - t u m b l e d c h e c k t u b e m .
2SFA = S n a c k F o o d A s s o c i a t i o n v i s u a l rating, s c a l e 1-5.
3NS = n o t significant; * = p v a l u e < 0.05; ** = p v a l u e < 0.01; *** = p v a l u e < 0.001
TABLE
4---Effect of N fertilizer applied and eultivar (or advanced breeding line) on post harvest quality characteristics
of stored tubers collected at two sampling dates (28-1-03 and 1 7 - 4 - 0 3 ) f i r m 2002field experiment at
Montcalm Research Farm, Entrican, MI.
N F e r t i l i z e r ( k g h a -~)
200
300
400
Cultivar
Snowden
MSG227-2
Liberator
Source of Variation
N Fertilizer
Cultivar
N Fertilizer x C u l t i v a r
Chip Color
SFA 1
-28-1-03
Sucrose
2002
pg mg ~
Glucose
2002
pg mg i
Chip Color
SFA
1.1
1.2
1.3
0.54
0.55
0.57
0.03
0.02
0.02
1.1
1.1
1.2
1.1
1.3
1.2
0.50 b
0.56 ab
0.01
0.02
1.3
1.0
0.60 a
0.03
1.0
NS
*
NS
NS
NS
NS
NS
NS
NS
NS 2
NS
NS
~SFA = S n a c k F o o d A s s o c i a t i o n v i s u a l rating, s c a l e 1-5.
2NS = N o t Significant; * = p v a l u e < 0.05; ** = p v a l u e < 0.01; *** = p v a l u e < 0.001.
-17-4-03
Glucose
2002
p g m g -~
Tuber
Nitrate
m g g-~
Total
Tuber N
m g g-~
1.12
1.19
1.10
0.14
0.15
0.15
0.003 b
0.006 a
0.006 a
15.8 b
17.1"
17.8 ~
1.62 a
1.14 h
0.65"
0.2@
0.1 lb
0.04 r
0.005 ab
0.008 a
0.002 b
15.9 b
18.8 ~
16.0 b
Sucrose
2002
pg mg l
NS
NS
*
**
9 *$
**
*
**
NS
NS
NS
NS
2004
LONG et al.: MICHIGAN CULTIVAR N RESPONSE
Nitrogen Response
A positive tuber yield response from 200 to 300 kg N h ~ ~
355
200 and 300 kg N ha -1rates. This supports the supposition that
excess N was applied with the 400 kg N ha 1 treatment. Tuber
was observed overall in 2001, whereas no further yield
N was influenced by genotype as well as by N fertility level, as
increase occurred from 300 to 400 kg N h ~ 1 (Table 1). Inter-
MSG227-2 tubers were consistently high in nitrate and total N
estingly, in 2001 there was a spacing-by-N interaction. The nar-
concentration, and Liberator tubers were generally low in
row spacing was associated with almost no yield response
nitrate-N (Table 4). Characterizing tuber nitrate-N content is
with enhanced N level, whereas at the wider row spacing all
important, as this may influence tuber processing quality and
lines responded to 300 kg N ha I by an increase in yield of about
nutrition characteristics (Amrein et al. 2003; Kolbe et al. 1995).
5 t ha -~, compared to 200 kg N ha-1 yield levels (Figure 1). In
Simulation modeling predicted that 360 kg N ha -1 is the
2002 there was no yield benefit associated with increasing N
theoretical maximum N fertilizer level associated with a yield
fertility from 200 to 300 kg N ha-l, and a slight but significant
response at ttus Michigan site for the cultivar Atlantic (Snapp
yield decrease occurred from 300 to 400 kg N ha 1(Table 2; Fig-
and Fortuna 2003). Earlier field studies in Michigan have indi-
ure 2). Size distribution was not markedly influenced by N fer-
cated that maximum potato yields and N conservation can be
tilizer rate, as indicated by the limited effect on weight of
obtained with good agronomic practices that include low to
B-sized tubers (Tables 1 and 2), and on oversize tubers (data
moderate N fertilizer levels, from 150 to 200 kg N ha (Joern
not shown).
and Vitosh 1995). Michigan potato producers have generally
Higher levels of N fertilizer were associated with slightly
reduced N fertilizer doses and adopted the use of petiole-N
reduced tuber specific gravity and enhanced external defects
monitoring to improve N fertilizer management (Snapp et al.
in both years (Tables 1 and 2). This is similar to observations
2001), but fltrther research is required to free-tune N fertilizer
of Belanger and colleagues (2002) investigating N response in
recommendations for specific cultivars, management prac-
Russet Burbank and Shepody. Other tuber quality characteris-
tices and environmental conditions. The study reported here is
tics influenced by N fertilizer were reduced internal defects in
one step in that process, indicating that new chip-processing and
2001 (Table 1) and elevated sucrose at harvest in 2002 (Table 3).
tablestock lines have moderately high N fertilizer requirements
In the current study N fertilizer levels did not influence
similar to earlier-released medium-to-long-durationcultivars.
sucrose or glucose in stored tubers (Table 4).
The N yield response observed was consistent with Michi-
Spacing Response
gan N recommendations for potato production. That is, opti-
Narrow seedpiece spacing tended to produce the highest
mal response of U.S. No. 1 tuber yield was observed from
potato tuber yields for all lines and N fertility levels. This was
application of 200 to 300 kg N ha -i, depending on yield poten-
shown in both years, as total tuber yields and U.S. No. 1 tuber
tial of the site and year, and taking into account N demand of
yields were increased 10 to 20% in narrow- vs wide-spaced
the cultivar grown (Snapp et al. 2002; Vitosh 1990). The supra-
seedpiece treatments (Figures 1 and 2; Tables 1 and 2). Plant
opthnum N fertility levels of approximately 400 kg N ha-: used
population density is higher with narrow seedpiece spacing
on occasion by potato growers (Lang et al. 1999; Snapp et al.
than with wide, and this is frequently associated with a rapid
2001) did not enhance yields in the study reported here. Peti-
rate of canopy closure and high yield potential (Creamer et al.
ole nitrate-N concentration varied over the growing season
1999; Waterer 1997). In the current study, rapid plant canopy
from 34,000 ppm (dry weight basis) early in the season to
coverage and high plant vigor ratings were consistently found
12,000 ppm late in the season in 2001, and from 28,000 to
in the narrow seedpiece spacing treatment (data not shown).
10,000 ppm in 2002. For all N fertilizer rates and cultivars
Earlier research indicated that a large tuber set and gen-
tested, petiole nitrate-N was consistently above the MSU rec-
erally small tubers were associated with the tablestock culti-
ommended critical value of 14,000 ppm at tuber initiation and
var Jacqueline Lee (Douches et al. 2001b). Large-sized tubers
10,000 ppm at tuber maturation (Snapp et al. 2002).
greater than B-sized (< 5.1 cm) are required for most markets.
An apparent "luxury" uptake of N occurred that did not
It is frequently possible to enhance average tuber size in pota-
contribute to tuber yield gain. Petiole nitrate-N (data not
toes through wider plant spacing (Arsenault et al. 2001). Thus,
shown), tuber N, and tuber nitrate-N levels (Table 4) were sig-
the widest seedpiece spacing evaluated in our study was for
nificantly higher with the 400 kg N h ~ 1 rate compared to the
the tablestock cultivar Jacqueline Lee. The concern was to
356
AMERICAN JOURNAL OF POTATO RESEARCH
deternfine ff tuber size could be increased through cultural
Vol. 81
Taken together, the data were consistent with the use of
management of this new cultivar. However, in the study
narrow seedpiece spacing to minimize N fertilizer require-
reported here minimal shifts in tuber size were found for
ments and to optimize yield response. These findh~gs have
Jacqueline Lee at widely varying seedpiece spacing.
environmental and crop management implications. Lower
doses of N fertilizer are associated with more efficient N nutri-
Interactions
Recent studies have shown that genotype often interacts
tion and are a reconunended management strategy for potato
production in Michigan (Snapp and Fortuna 2003; Vitosh
with management to influence the proportion of U.S. No. 1
1990). At the same time seed tubers are one of the most expen-
tubers to B-sized tubers. At Prince Edward Island wide seed-
sive costs of production for potato farmers (Darttand Schwab
piece spacing was associated with reduced weight of B-sized
2001). The expense associated with a narrow seedpiece spac-
tubers in five out of eight cultivars investigated (Arsenault et
ing (higher numbers of seedpieces) must be considered and
al. 2001). Seedpiece spacing altered tuber size distribution in
evaluated in relationship to advantages such as rapid canopy
other research as well (Creamer et al. 1999; Love and Thomp-
coverage and reduced N fertilizer requirements. A contrasting
son 1999). In the study reported on here, MSE192-8 tuber size
N response and seedpiece spacing interaction has been
distribution was altered by seedpiece spacing: the proportion
observed in seed potatoes, where yield response to increasing
of B-sized tubers in 2001 was 12.1% for narrow seed spacing
levels of N fertilizer increased with narrow seedpiece spacing
and 7.6% for wide seedpiece spacing. In 2002, the shift in pro-
(Waterer 1997).
portion of B-sized tubers in MSE192-8 was much smaller, from
3.2% to 2.1%. Overall, the effect of seedpiece spacing on tuber
Conclusion
size profile was marked in 2001 for MES192-8 and Jacqueline
The cultivars tested here demonstrated excellent storage
Lee, but in other cultivars there was minimal influence of nar-
characteristics across moderate to supra-optimum N fertility.
row versus wide seedpiece spacing. A relatively short potato
The consistency and high quality of tuber characteristics
growing season in Michigan may, in some cultivars and sea-
observed reflects a long-term commitment to selecting for
sons, limit tuber bulking and help explain the moderate shifts
tuber quality characteristics in the Michigan potato program.
observed in tuber size profile.
Overall, the recommended N fertilizer level for moderately
There was a trade-off between plant population density
long-duration potato cultivars in Michigan (200 kg N ha -1) and
and N fertility management during 2001 (Table 1). Narrow
a narrow seedpiece spacing (0.20 to 0.25 m) optimized yield
seedpiece spacing was associated with early plant vigor (data
and tuber quality performance in the five cultivars evaluated.
not shown) and maximum yield potential at 200 kg N ha -l, the
This combination of agronomic practices was associated with
recommended N level. At a wider seedpiece spacing a positive
the highest N fertilizer efficiency, as indicated by tuber yield
yield response was observed to a higher N fertilizer input level
per N fertilizer applied and by plant N status. Narrow seed
of 300 kg N h ~ 1, compared to yield at 200 kg N hw 1(Figure 1).
spacing and 200 kg N ha 1 was also consistently associated
In 2001 there was no total tuber yield response to the highest
with the highest quality tuber characteristics. As potato seed-
N fertilizer level of 400 kg N ha -l, regardless of seedpiece spac-
pieces are a significant production costs, there are economic
ing (Figure 1). Tuber nitrate-N and total N concentration was
consequences of using narrow spacing. Farmers must evaluate
substantially increased at the highest N fertilizer level, partic-
the trade-offs between increased costs at high seedpiece den-
ularly for the line MSG227-2 (Table 4). Conversely, petiole
sities and the potential for higher yields and more efficient N
nitrate-N was lowest for MSG227-2 at the final measurement
fertilizer use.
107 days after planting (data not shown). This is consistent
with efficient remobilization of N from leaves to tubers in line
MSG227-2, although further study is needed to confirm this
observation. Earher studies have found that genotype can
influence petiole nitrate-N concentration (Belanger et al. 2003;
Waterer 1997).
2004
LONG e t al.: MICHIGAN CULTIVAR N R E S P O N S E
357
LITERATURE CITED
Lewis RJ, and SL Love. 1994. Potato genotypes differ in petiole nitratenitrogen concentrations over time. HortScience 29:175-179.
Amrein TM, S Bachmann, A Noti, M Biedermmm, MF Barbosa, S Biedermann-Brem, K Grob, A Keiser, P Realini, F Escher, and R
Amado. 2003. Potential of acrylamide formation. J Agric Food
Chemistry 51:5556-5560.
Love SL. 1999. Founding clones, major contributing ancestors, and
exotic progenitors of prominent North American potato cultivars. Amer J Potato Res 76:263-272.
Love SL, and JA Thompson. 1999. Seed piece spacing influences yield,
tuber size distribution, stem and tuber density, and net returns
of three processing potato cultivars. HortScience 34:629-633.
Arsenault WJ, DA LeBlanc, GCC Tai, and P Boswall. 2001. Effects of
nitrogen application and seedpiece spacing on yield and tuber
size distribution in eight potato cultivars. Amer J Potato Res
78:301-309.
Baritelle AL, GM Hyde, and RE Thornton. 2000. Influence of early-season nitrogen application pattern on impact sensitivity in Russet
Burbank potato tubers. Postharvest Biol Tech 19:273-277.
Belanger G, JR Walsh, JE Richards, PH Milburn, and N Ziadi. 2002.
Nitrogen fertilization and irrigation affects tuber characteristics
of two potato cultivars. Amer J Potato Res 79:269 279.
Belanger G, JR Walsh, JE Richards, PH Milburn, and N Ziadi. 2003. Critical petiole nitrate concentration of two processing potato cnitivars in Eastern Canada. Amer J Potato Res 80:251-261.
Creamer NG, CR Crozier, and MA Cubeta. 1999. Influence of seedpiece
spacing and population on yield, internal quality, and economic
performance of Atlantic, Superior, and Snowden potato varieties in eastern North Carolina. Amer J Potato Res 76:257-261.
Dartt B, and GD Schwab. 2001. Crops and livestock budget estimates
for Michigan. Agricultural Economics Report No. 609. Dept. Agricultural Economics, Michigan State University, East Lansing.
Douches DS, K Jastrzebski, J Coombs, RW Chase, R Hammerschmidt,
and WW Kirk. 2001a. Liberator. A round white chip-processing
variety witt: resistance to scab. Amer J Potato Res 78:425432.
Douches DS, K Jastrzebski, J Coombs, WW Kirk, KJ Flecher, R Hammerschmidt, and RW Chase. 2001b. Jacqueline Lee: A late-blightresistant tablestock variety. Amer J Potato Res 78:413-420.
Herman TJ, SL Love, B Shafii, and RB DweUe. 1996. Chipping performance of three processing potato cultivars during long-term storage at two temperature regimes. Amer Potato J 73:411-425.
Joem BC, and ML Vitosh. 1995. Influence of applied nitrogen on potato.
1.Yields, quality and nitrogen uptake. Amer Potato J 72:51-63.
Kolbe H, K Muller, G Olteanu, and T Gorea. 1995. Effects of nitrogen,
phosphorous and potassium fertilizer treatments on weight-loss
and changes in chemical-compositionof potato-tubers stored at
4-degrees-C. Potato Res 38:97-107.
Lang NS, RG Stevens, RE Thornton, WL Pan, and S Victory. 1999. Potato
nutrient management for central Washington. Extension Bulletin No. 1871. Cooperative Extension, Washington State University, Pullman.
Salazar M, and L Busch. 2001. Standards and strategies in the Michigan
potato industry. Research Report 576. Michigan Agricultural
Experiment Station.
Snapp SS, H Borden, and DD Rohrbach. 2001. Improving nitrogen efficiency: lessons from Malawi and Michigan. In: J Galloway, E
Cowling, JW Erisman, J Wisnieswki, and C Jordan (eds), Optimizing Nitrogen Management in Food and Energy Production
and Environmental Protection. Second International Nitrogen
Conference Papers, A.A. Balkema Pub. Lisse/Abingdon/Exton/
Tokyo. pp. 42-48.
Snapp SS, and A Fortuna. 2003. Predicting nitrogen availability in irrigated potato systems. HortTechnology 13:598-604.
Snapp SS, J Nyiranez, and K O'Neil. 2003. Organic inputs and a cover
crop-short rotation for improved potato productivity and quality. In: Michigan Potato Research Report, Vol. 34. Michigan State
University, Agricultural Experiment Station in cooperation with
The Michigan Potato industry Commission, East Lansing. pp.
139-144.
Snapp SS, D Smucker, and M Vitosh. 2002. Nitrogen management for
Michigan potatoes. Michigan State University Extension Bulletin E2779.
Sowokinos JR. 2001. Biochemical and molecular control of coldinduced sweetening in potatoes. Amer J Potato Res 78:221-236.
Vitosh ML. 1990. Potato fertilizer recommendations. MSU Extension
Bulletin E-220. Michigan State University, East Lansing.
Waterer. 1997. Influence of irrigation, nitrogen and seed piece spacing
on yields and tuber size distribution of seed potatoes. Can J
Plant Science 77:141-148.
Westermaim DT, DW James, TA Tindall, and RL Hurst. 1994. Nitrogen
and potassium fertilization of potatoes - - sugars and starch.
Amer Potato J 71:433453.