FLORIDA STATE HORTICULTURAL SOCIETY, 1959
202
FACTORS AFFECTING SPECIFIC GRAVITY OF POTATOES
at
of
in
as
Donald L. Myhre
Potato Investigations Laboratory
Hastings
Numerous workers have shown that potato
quality is directly associated with dry matter
content. Specific gravity has been used as a
criterion of potato quality because of its close
relationship to dry matter content and the
rapidity with which it may be determined
(4, 7). High specific gravity potatoes are
better suited for baking, frying, mashing and
chipping; low specific gravity for boiling and
canning (6). The potato chip manufacturers
prefer potatoes of high specific gravity be
cause they yield more chips per pound of po
tatoes (2). This outlet for potatoes is im
portant to the potato industry at Hastings be
cause over two million bushels of the annual
crop are sold for chips.
Many attempts have been made to corre
late variations found in specific gravity of
tubers with cultural practices and environ
mental conditions. Variety has been reported
by many workers to be the most important
factor determining potato quality. Soil type
affects specific gravity of tubers through its in
fluence on soil temperature, soil moisture and
uptake of nutrients. Potatoes grown on sandy
loam soils- were found to be of higher quality
than those grown on clay soils (8). Heavy
fertilization, particularly with nitrogen or
potash, usually results in tubers of lower
specific gravity (5). Conflicting results have
been obtained from attempts to determine the
influence of soil moisture on specific gravity
of potato tubers.
This paper attempts to summarize the in
fluence of some factors on specific gravity of
potato tubers grown in the area adjacent to
Hastings, Florida.
Potato seedpieces were planted in January
and tubers harvested in late April or early
May. Length of growing season was varied in
some studies by harvesting at different dates.
Fertilizer containing one-half chloride and
one-half sulfate of potash was applied in bands
Agricultural
Experiment
Station
Journal
sub-irrigation.
Specific gravity was measured by a potato
hydrometer attached to a wire basket con
taining eight pounds of medium-sized potato
tubers immersed in water. Measurements were
made on potatoes grown in the field under
various cultural and environmental conditions.
Each specific gravity value in the tables repre
sents the mean of at least five determinations.
The percentages of starch and dry matter or
total solids were calculated from specific
gravity measurements using the regression
equations of C. Von Scheele (3).
Results and Discussion
Varieties.—A numbered seedling, B3677-1,
had the lowest specific gravity of 1.0642 and
B606-3 had the highest specific gravity of
1.0824 as given in Table 1. These specific
gravity values would correspond approximately
TABIZ 1.- Specific Gravity and Calculated Percentages of Starch
and Total Solids of Potato Varieties and Seedlings, 1956-59.
Potato Variety
or Seedling1
B6O6-3 (1)
hPC-5 (1)
B3626-15 (1)
Fundy (1)
B313-21 (1)
Kennebec (1)
6536 (1)
Merrimack (2)
Tawa (1)
B929-23 (1)
I.O82I4
1.0821
1.0812
1.0780
1.0778
1.0770
1.0765
1.0762
1.0760
1.0757
Delus (3)
1.0756
WCU956 (1)
1.O7U8
1.O7U2
liRM-3 (2)
1859 (1)
B3725-1 (2)
B36O2-I4 (3)
36714 (1)
Saco (1)
B2368-Ii (1)
Cherokee (1)
Pungo (h)
Sebago (h)
Plymouth (k)
Red Pontiac (2)
B3677-1 (2)
% Total
Specific
Gravity
1.0751
I.07I1I
1.0735
1.073k
1.0725
Starch
Solids
Ui.3
20.7
20.7
11.2
Hi.l
13.U
Series,
20.5
13 »h
19.8
19.7
19.6
13.1
19.5
19. h
19.h
13.2
13.1
13.0
13.0
13.0
12.8
12.8
12.7
12.7
12.5
12.5
12.3
1.0716
1.0719
1.0717
12.2
12.2
12.2
1.0675
1.O65U
1-O6li2
1.0696
11.8
11.3
10.9
10.7
^Number in parentheses refers to number of years
Experimental Procedure
Florida
No. 990.
planting at the rate of about 2,500 pounds
6-8-8 per acre, unless otherwise specified
the tables. Supplemental water was applied
needed by the water furrow method of
19.3
19.3
19.2
19.1
19.1
19.0
18.8
18.8
18.6
18.5
18.5
18.U
18.0
17.6
17.1
16.9
measurements
were made.
to yields of 28 and 32 pounds of chips per
hundred pounds of potatoes according to the
National Potato Chip Institute. Sebago, which
has been the leading commercial variety plant
ed at Hastings since 1942 (1), had a relatively
low specific gravity of 1.0696. However, large
quantities of Florida Sebago potatoes have
MYHRE: POTATO SPECIFIC GRAVITY
been purchased by potato chip manufacturers
because they produce very crisp chips of uni
form, light color which is more important than
specific gravity (2).
Soil Type.—Rutledge, Leon and Bladen soils
produced potato tubers which had specific
gravities of 1.0655, 1.0606 and 1.0591, respec
tively, as given in Table 2. A difference of
TABLE U.- Effect of Length of Growing Season, Method of
Fertilizer Application and Quantity of Potash on
Specific Gravity of Sebago Potatoes in 1959*
Rutledge f.s.
'6.00
5.13
U.27
5.37
80
35
Bladen f.s.
Measurements
Soil pH
Moisture Equivalent, %
Calcium, p.p.m.
Potassium, p.p.m.
Phosphorus, p.p.m.
Specific Gravity
5.89
30
1.0591
6.36
1,66
5U
27
U16
8
1.0606
1.0655
cant for practical purposes by some potato
chip manufacturers. On this basis, the specific
gravity of tubers grown in Rutledge fine sand
was significantly higher than that of tubers
grown in Leon and Bladen fine sand. There
was no correlation between specific gravity of
potato tubers and any of the soil factors
measured.
Source of Potash.—Data are given in Table
3. Generally, sulfate of potash in the fertilizer
produced tubers of higher specific gravity than
TABLE 3.- Effect of Source of Potash and Length of Growing
Season on Specific Gravity- of Sebago Potato Tubers.
Year
19ft
1955
1956
Days
Rainfall,
Inches
105
98
5.28
5.86
Season,
109
103
127
83
6.77
5.57
12.18
7.20
Specific Gravity
Sulfate
Chloride
1.0610
1.0621*
1.0608
1.070l*
1.0621*
1.0639
1.0673
1957
102
1958
112
132
lli.86
17.66
1.0692
1959
91
lit.99
17.0U
1.O7OC5
112
106
7.31
7.71*
1.0700
1.0720
1.0721
1.0650
1.0661*
1.0637
1.0707
l'.0695
1.0721*
1.0687
1.0682
1.0726
1.071*2
when chloride was the source of potash. Ex
ceptions occurred at the second harvest in
1956 and both harvests in 1958 when rainfall
was excessive. Plants were sidedressed with
200 pounds of nitrate of soda-potash 52 days
before the first harvest in 1958 which may
have influenced the specific gravity of the
tubers.
Rate of Potash.—Specific gravity of tubers
was decreased significantly (1 percent level)
by using 300 pounds of potash instead of the
conventional 200 pounds per acre as shown in
Table 4.
Lbs./A
Application
Specific Gravity
91 Days
112 Days
1.0720
1.0722
1.0688
I.O696
Band
100
200
300
1.0730
1.07149
Broadcast
200
1.0757
1.07*5
.0016
.0031
.001*2
L.S.D. % Level
L.S.D. \% Level
.0022
^•Soil contained lJ>0 pounds of exchangeable potash per
acre.
Tubers in 195U.
Leon f.s.
Potash,1
Method of
6.0025 in specific gravity is considered signifiTABIE 2.- Effect of Soil Type on Specific Gravity of Sebago Potato
203
Hate of Nitrogen.—Data were obtained, but
not presented here, which showed that up to
300 pounds of supplemental nitrogen per acre
did not significantly affect specific gravity of
tubers in 1959.
Method of Fertilizer Application.—Broadcast
application of fertilizer containing 200 pounds
of potash per acre increased specific gravity
of tubers significantly (1 percent level) com
pared to band application as shown in Table
4.
Length of Growing Season.—Specific gravity
decreased between the dates of harvest in
1955, 1956 and 1958, while the converse was
true in 1957 and 1959. It appears that the
effect of the length of growing season on
specific gravity depends upon the length of
time needed to reach physiological maturity,
which is defined as the point in the growth
cycle of the potato when maximum specific
gravity occurs. The time needed to reach
maturity varied slightly in different years as
shown in Table 3.
Soil Moisture-The effect of the distance of
the row from the irrigation furrow is given in
Table 5. Specific gravity of tubers increased
as the distance from the irrigation furrow in
creased. Water was maintained in the irriga
tion furrows for 14 days of the 105-day grow
ing season.
TABIE 5-- Effect of Distance of Row from
Irrigation Furrow on Specific Gravity
of Sebago Potato Tubers in 19$$.
Feet from
Irrigation Furrow
Specific
Gravity
5
1.0635
55
1.0655
30
1.061(2
FLORIDA STATE HORTICULTURAL SOCIETY, 1959
204
Conclusions
Specific gravity ranged from 1.0824 to
1.0642 due to varietal differences. Rutledge
and Leon fine sand produced tubers of higher
specific gravity than Bladen fine sand. Lower
specific gravity values were usually associated
with high rates of potash, chloride as the
source of potash, band application of fertilizer
and higher levels of soil moisture.
Acknowledgement
The author expresses appreciation to the
following for their assistance. Drs. R. A. Dennison and C. B. Hall, Main Station, Gainesville,
for specific gravity measurements presented in
Table 4; Dr. G. M. Volk, Main Station, Gaines
ville, for data given in Table 2 and specific
gravity measurements in 1954 and 1955 in
Table 3; Mr. James Watts, Wise Potato Chip
Company, Berwick, Pennsylvania for specific
gravity measurements given in Table 1 for
1956-59; Dr. E. N. McCubbin for supplying
tuber samples of potato varieties and seedlings.
LITERATURE
CITED
1.
Eddins, A. H. and E. N. McCubbin. Improvements in
potato varieties and yields at Hastings, Florida. Fla. Soil
Sci. Soc. Proc. 13: 79-82. 1953.
2.
Goldstein, Aithur. A chip off the old potato. Proc. Fta.
State Hort. Soc. 68: 131-132. 1955.
3. Murphy, Hugh J. and Michael J. Goven. Factors af
fecting the specific gravity of the white potato in Maine.
Maine Agr. Exp. Sta. Bui. 583. 1959.
4. Schark, Allen E., C. E. Peterson and Frances Carlin.
The influence of variety on the specific gravity-mealiness
relationship of potatoes. Amer. Potato Jour. 33: 79-83. 1956.
5.
Terman,
6.
United States Department of Agriculture. Agr. Res. 7:
14-15.
G.
L.
Maine Agr.
Exp.
Sta.
Bui.
481.
1950.
1955.
7.
Vanasse, Norman A., Evan D. Jones and Henry L.
Lucas. Specific gravity-dry matter relationship in potatoes.
Amer. Potato Jour. 28:781-791. 1951.
8. Willaman, J. J. and R. M. West. Minn. Univ. Studies
Biol. Sci. 5: 211. 1924.
USE OF COMBINATIONS OF MANEB AND DYRENE FOR
CONTROL OF TOMATO DISEASES
weaknesses as tomato fungicides. Ferbam and
thiram do not adequately control either late
blight or gray leaf spot. Dichlone, although
effective against late blight, does not control
gray leaf spot and may be phytotoxic, especial
ly in hot weather.
Coe and Conover (1) reported that Dyrene
was more effective than maneb against gray
leaf spot, but less effective against late blight.
Research since then at the Sub-tropical Experi
Robert A. Conover
Plant Pathologist
Sub-Tropical Experiment Station
Homestead
and
Robert E. Stall
Assistant Plant Pathologist
ment Station and Indian River Field Labora
tory, in addition to confirming these results,
has also demonstrated that maneb is adequate
Indian River Field Laboratory
Fort Pierce
Use of the ethylene bisdithiocarbamate fungi
cides, particularly maneb, by Florida growers
has resulted in a marked improvement in con
trol of fungus diseases of tomato in recent
years. When properly applied maneb gives
excellent control of late blight (Phytophthora
infestans (Mont.) DBy) and adequate control
of gray leaf spot (Stemphylium solani Weber)
under most conditions. The major shortcoming
of maneb as an all-purpose tomato fungicide
is that it does not control Botrytis gray mold
(Botrytis cinerea Fr.). Ferbam, thiram and
dichlone have been suggested for control of
Botrytis gray mold (2,3) but all have major
Florida
No. 963.
Agricultural
Experiment
Station
Journal
Series,
for gray leaf spot control when frequent appli
cations can be made on a regular schedule.
The superiority of Dyrene over maneb has
been manifested when gray leaf spot is epi
demic, or when it is severe and applications
are missed, or applied at weekly or longer
intervals. Thus Dyrene has little advantage
over maneb against gray leaf spot under rou
tine conditions, but it is quite helpful when
more protection against gray leaf spot is re
quired.
Stall (4, 5) reported that Dyrene was equal
to dichlone for the control of Botrytis gray
mold, and, in addition, Dyrene was less phy
totoxic than dichlone.
Thus Dyrene, like
maneb, has features useful in the tomato dis
ease control program, but it also has some