November, 1948
EFFECTS of
TIME of PLANTING and DIGGING on
YIELD and GRADE of SWEETPOTATOES
in SOUTHERN ALABAMA
T. P. WHITTEN, Assistant Horticulturist
Sweetpotato yields 
may be dou-
bled or even trebled by planting
earlier and digging later. 
Of all
the things a farmer 
can control
and do, time between planting
and digging has the 
greatest ef-
fect on yields from 
fertile soils.
Yields alone, however, are 
not
the only basis for deciding 
the
time of planting and digging.
Grades, marketing seasons, 
in-
tended uses of the crop, and
market prices will often deter-
mine when the crop should be
planted and harvested 
for maximum
returns. Thus, knowledge 
of ex-
pected yields of No. 
l's and
other grades at given 
periods
from plantings made 
at different
times is important 
to the grower
in deciding his plan of 
pro-
duction.
Reported here are impoitant re-
sults from experiments in sweet-
potato production in southern
Alabama by the Alabama Agricul-
tural Experiment Station.
CHOICES OPEN to GROWER
There are three choices open
to a sweetpotato grower in southern
Alabama. He may grow an early
crop from an early planting, a
late crop from an early planting,
or a late crop from a late plant-
ing.
To obtain a satisfactory yield
of potatoes for sale by midsummer,
it requires early planting. Only
slips are available for this
planting. Prices for potatoes
may be high in midsummer. 
Good
returns, therefore, may be 
ob-
tained even with a medium 
yield.
Fairly good yields, however, 
may
be made by August if 
the crop
is planted early enough.
High yields of potatoes may
be expected from the crop if
planted early and dug late. Such
type of production is best adapted
to a program that combines market-
ing the better grades and process-
ing or feeding the lower grades.
The late-planted crop is suited
to an operation where production
of high-quality potatoes either
for market or seed purposes is
the principal aim. This crop
usually will be planted from vine
cuttings. Better shaped roots
and less disease will result from
late-planted vine cuttings than
from early-planted slips.
Growers may specialize in one
type of production or more likely
most growers will be concerned
with all three types of production.
SCOPE of the EXPERIMENT
The experiment reported in this
publication was designed to answer
some of the auestions in regard
to yields and grades of potatoes
AGRICULTURAL EXPERIMENT 
STATION
of the ALABAMA POLYTECHNIC INSTITUTE
Leaflet 25
M. J. Funchess, D;rector Auburn, Alabama
produced when planted from slips
at different dates and harvested
at different dates.
The results represent 3 years'
experimental work. Plantings were
made at three periods and potatoes
dug at six periods. The experiment
was conducted at Atmore on a good
grade of Red Bay soil. The variety
used was Porto Rico. Fertilizer
treatment consisted of 800 pounds
per acre of 4-10-7 applied at
planting time plus 100 pounds per
acre of nitrate of soda applied
just as the vines began 
to run
Plants were set 16 inches apart.
All treatments were repeated on
three different sets cf plots in
order to obtain more dependable
results.
Results of Experiments
Yields of No. 1 potatoes and
total yields of potatoes from
each combination of the three
planting dates and the six dig-
ging dates are given in Table 1.
Increases in yields of potatoes
from earlier plantings over yields
of those planted later are given
in Table 2.
Increases in yields of potatoes
dug at different dates over the
yields of potatoes dug at earlier
dates are given in Table 3.
The records in Table 1 permit
a comparison of the yields of
potatoes obtained from any of the
planting dates when dug at any
of the digging periods.
High Yields Result from Long
Grow ing Season
The yield of No. l's and of
all grades increased consistently
from the earliest planting date
to the latest digging date, Table
1. With the exception of one in-
stance, the yield at each digging
date was larger than the previous
date. It should be pointed out
that the larger increases occurred
in the early part of the harvest
se ason, Table 3.
For example, at the first dig-
ging (July 29), which was 105
days after planting (April 15),
the yield was 70 bushels per acre
of No. 1 potatoes. At the next
digging date (August 16), the acre
yield was 148 bushels. This is
an increase of 78 bushels of
No. l's over that harvested July
29. In other words, 18 additional
growing days increased the yield
over 100 per cent. The yield of
No. 1 potatoes dug August 28 was
198 bushels per acre, or 50 bush-
els more than that harvested 12
days earlier (August 16). With
each successive digging date
during the remainder of the season,
increases in yields of No. l's
became progressively less. For
instance, the yield of potatoes
dug September 15 was only 35
bushels higher than that dug
August 28 -- 18 days earlier. In
the last 36 days, the increase
of potatoes dug October 21 was
only 32 bushels over the yield
of those dug September 15.
In all, the increased yield
of No. 1 potatoes dug October 21
over that harvested July 29 a-
mounted to 195 bushels per acre.
Thus, 84 more growing days gave
about 2-3/4 times as many No. 1
p0 t at0e
potatoes .
Similar increases in No. 1
potatoes were obtained for each
longer growing period in both
cases of the later planting dates.
The increases in the total
yield of potatoes for each longer
growing period were even more
striking than the increases in
the yield of No. 1 potatoes. For
instance, the total yield of po-
tatoes planted on April 29 and
dug on July 29 was 116 bushels.
In 18 more growing days the yield
had increased 93 bushels, in 12
more growing days another 63 bush-
els, in 19 more growing days an-
other 69 bushels, in 18 more
growing days another 30 bushels,
and in 17 more growing days an-
other 67 bushels.
The largest increase in the
yield of potatoes between planting
dates and digging dates amounted
to 255 bushels per acre of No. l's
and 403 bushels of all grades.
Early Planting Necessary for
Early Crop
Early planting is necessary
for a high yield of early po-
tatoes, Table 1. Yield of No. 1
potatoes from the May 16 planting
was only 26 bushels per acre by
August 16, and from the April 29
planting it was only 54 bushels.
On the other hand, yield from the
April 15 planting on August 16
was 148 bushels. Py August 28 the
yields of No. 1 potatoes from
these 3 planting dates were 77,
116, and 198 bushels per acre,
respectively.
Early Planting Gives Increases
in Yields Over Late Planting
It may be noted (Table 2) that
the increases in the total yield
of potatoes planted April 15 over
those planted May 16 for the dif-
ferent harvest dates ranged from
133 to 164 bushels per acre. The
average increase was 143 bushels.
This means that there was a loss
of 36 bushels per acre each week
planting was delayed after April
15 and until May 16. The loss per
week was about 47 bushels per
acre for each week's delay be-
tween April 15 and April 29,
whereas the loss was only 23
bushels per acre for each week
planting was delayed between April
29 and Mav 16.
The increase in the yield of
of No. 1 potatoes planted April
15 over those planted April 29
was much higher when. dug early in
the season than when dug late.
The increases in yield of No. l's
were 94 and 82 bushels per acre
for those dug August 16 and August
28, respectively, whereas the
increases were only 42 and 56
bushels, respectively, for those
dug October 4 and October 21. On
the other hand increases of No.
1 potatoes from April 29 planting
over May 16 planting were about
the same for the six digging dates.
These differences ranging from 28
to 39 bushels per acre and aver-
aging about 34 bushels at each
digging period.
Large increases Obtained from
Late Digging Over Early Digging
The increased yields (Table 3)
of No. 1 potatoes dug October 21
over those dug August 16 were 117
bushels per acre from the April
15 planting, 155 bushels per acre
from the April 29 planting, and
150 bushels from the May 16 plant-
ing. The increased yields of all
grades of potatoes dug October 21
over those dug August 16 were
229, 216, and 203 for the three
successive planting dates.
Potatoes dug October 21 had
p;oduced 194 bushels per acre of
No. l's and 322 bushels per acre
of all grades more than those
dug July 29.
HOW to USE RESULTS
The results in the tables per-
mit a varied number of compari-
sons. For instance, the information
will help the grower choose be-
tween (1) selling his crop early
in the season when prices may be
high but yield is below the maxi-
mum, or (2) holding his crop for
later harvest and sale when yields
are higher and prices may be lower.
As an example, the yield of 148
bushels per acre of No. l's dug
August 16 from 
April 15 planting
and sold at 6 to 8 cents per
pound would bring $444 to $592.
The yield of 233 bushels per acre
dug September 15 from April 15
planting and sold at 4 to 6 cents
would bring $466 to $699. The
higher price at the earlier dig-
ging period might, therefore,
pertly cancel out the value of the
higher yield obtained at the
later digging period.
The results should apply to the
southern fourth of the State on
land capable of producing 300 to
400 bushels per acre when the
crop is planted early and dug
late.
On land producing lower total
yields than these, smaller dif-
ferences will be obtained between
potatoes planted at different
dates and dug at different dates.
Table 1.- Yields of No. l's and All Grades of Sweetpotatoes Set and Dug
at Different Dates, 3-Year Average, 1945-47
Average Yield by different digging dates
planting
date July 29
1
August 16 August 28September 15 October 4 October 21
Bushels per acre, No. I's
April 15 70 148 198 233 231 265
April 29 10 54 116 174 189 209
May 16 -- 26 77 141 151 176
Bushels per acre, all grades
April 15 116 209 272 341 371 438
April 29 35 110 176 252 288 326
May 16 -- 71 128 202 238 274
Table 2.- Increase in Yields of Potatoes from Earlier Planting,
3-Year Average, 1945-47
Average Increase in yield from earlier planting dates
planting over later dates at six digging periods
date July 291Aug. 16 Aug. 281Sept. 15Oct. 44 Oct. 21
Increase in bushels per acre, No. l's
Apr. 15 over
Apr. 29 61 94 82 59 42 56
Apr. 29 over
May 16 28 39 33 38 33
Apr. 15 over
May 16 -- 122 121 92 80 89
Increase in bushels per acre, all grades
Apr. 15 over
Apr. 29 81 99 96 89 83 
112
Apr. 29 over
May 16 -- 39 38 50 50 52
Apr. 15 over
May 16 -- 138 144 139 
133 164
Table 3.- Increase in Yield of Potatoes Resulting from Delayed
Harvest, 3-Year Average, 1945-47
Average Increase in Yield over earlier digging periods
planting Aug. 16 Aug. 28 Sept. 15 Oct. 4 Oct. 21 Oct. 21 Oct.
date over over over over over over over
July 29IAug. 161 Aug. 281Sept. 15 Oct. 4 Aug. l6July 29
Increase in bushels per acre, No. I's
April 15 78 50 35 -2 34 117 195
April 29 44 62 58 15 20 155 199
May 16 -- 51 64 10 25 
150 ---
Increase in bushels per acre, all grades
April 15 93 63 69 30 67 229 
322
April 29 75 66 76 36 38 216 291
May 16 -- 57 74 36 36 203 ...