The term "potato," when not modified by an adjective, suggests to
the mind of an American the so-called potato (_Solanum tuberosum_).
When the name is modified by the word "sweet," reference is made to
a different plant, belonging to the morning-glory family and known
botanically as _Ipomoea batatas_. Attention is here directed entirely
to the Irish potato.
_Soil and Rotation._--The potato is grown in every State and Territory,
and naturally on a great variety of soils. Indeed, it has been grown
on nearly every class of soils, but this fact does not minimize the
importance of selecting for the potato the kind of soil best adapted
to it. The ideal soil for this crop should be one so light as to offer
no great resistance to the enlargement of the tubers, so supplied with
organic matter as to be rather moist without being wet, and so rich
as to furnish an unfailing supply of fertilizing ingredients. A rich,
sandy loam abundantly supplied with organic matter and naturally well
drained is preferable. Stiffer soils may be rendered suitable for
the potato by drainage and by the incorporation of farm manures; or
better, by plowing under green crops. Very heavy clay should be avoided
if the farm contains any lighter soil. Recently cleared ground suits
the potato. Sandy soils, if not too subject to drought, may be fitted
for this plant by the addition of organic matter. It is claimed that
potatoes grown on sandy land are of better quality than those grown on
stiffer soil.
The potato requires a rich soil, but even more important than natural
fertility is a proper mechanical condition of the soil. Artificial
fertilizers may be substituted in part for natural fertility, but they
are effective only when the soil is in such a condition as to furnish a
constant supply of water. The potato should have the best soil on the
farm, since it is more exacting in this respect than the other staple
crops and since the product of an acre is generally of greater value.
The success of the potato is largely dependent on the crops preceding
it in the rotation. If clover, cowpeas, or other leguminous plant is
grown just preceding potatoes, its stubble furnishes organic matter and
adds to the store of available nitrogen in the soil. Corn after sod
frequently precedes potatoes, and this is generally regarded as the
best rotation.
Rye is sometimes sown in late summer or fall and plowed under so as
to lighten a heavy soil. Buckwheat and other plants have also been
used for the same purpose. On light soils and in rather mild climates,
crimson clover for green manuring may advantageously take the place of
rye where early planting of potatoes is not specially desirable. One
year, or at most two years, is as long as a field should be devoted
to continuous potato culture, although this crop is sometimes grown
for more than two years in succession on the same land. This latter
course taxes heavily the fertility of the soil and necessitates liberal
manuring; moreover it involves considerable risk of injury from fungous
diseases, especially from potato scab. A clean crop of potatoes can
not, as a rule, be grown on land which in the preceding year produced
scabby tubers. The germs of the disease once in the soil must be
starved out by growing on the infected field other crops, such as grass
or grain, for several years. In certain localities in the central part
of the United States and elsewhere the following three years' rotation
has given highly satisfactory results on farms where potatoes are
extensively grown; Fall wheat, in which clover is seeded in the spring;
second year, clover, plowed under in fall or winter; and third year,
potatoes. In some localities the uncertainty in obtaining a catch of
clover renders this rotation inexpedient.
Detailed directions for the preparation of one class of soils would not
apply to others, hence it can only be said that preparation should be
deep and thorough, and that unnecessary compacting of the soil should
be avoided. Plowing can scarcely be too deep, provided that much of
the subsoil is not brought to the surface; when practicable, the depth
should be gradually increased from year to year. Though the tubers
are usually formed within 6 inches of the surface of the ground, the
roots feed deeper. Practical experience, as well as the extent of the
distribution of potato roots in the soil, emphasize the importance of
deep and thorough preparation of the soil for this crop. Whether fall
plowing is advisable depends on a variety of local considerations. In
general in a mild climate fall plowing of light land exposes it to
leaching; on the other hand, fall plowing is sometimes necessary, as,
for example, when a field is badly infested with injurious insects.
_Fertilizing._--The potato requires liberal manuring. Barnyard manure
usually affords a large increase in the crop, for not only does it
supply nitrogen, phosphoric acid, and potash, but it improves the
mechanical conditions of the soil. However, its direct application to
the potato affords conditions favorable to potato diseases, and thus
injures the quality of the crop. For this reason the best practice is
to apply barnyard manure to corn or grass the year before the potatoes
are grown. If it is considered necessary to apply it directly to the
potato crop it should first be well rotted.
If for several years before potatoes are planted the land has been
properly manured with farm manures, or with green crops plowed
under, commercial fertilizers can be advantageously used on most
soils. Generally, a complete fertilizer should be used--i. e., one
which contains nitrogen, phosphoric acid, and potash. The farmer is
justified in supplying all three of these fertilizing ingredients,
unless by previous tests he has learned that on his soil a certain one
of them can be safely omitted. Of nitrogenous fertilizers, one of the
best for potatoes is the quick-acting nitrate of soda. Of phosphatic
fertilizers, superphosphate is preferred. Among potash fertilizers
the sulphate of potash has been found to afford a better quality of
potato than kainit and muriate of potash. Ashes, are extensively and
effectively used to supply potash to potatoes.
As little farmyard manure is available in the Southern States where
the early crop of potatoes is chiefly produced, this seldom enters as
a factor in the production of the crop. Commercial fertilizers of a
nature especially adapted to the potato crop form the chief reliance
of the growers. A fertilizer carrying 3 to 4 per cent of nitrogen, 6
to 8 per cent of phosphoric acid, and 8 to 10 per cent of potash is
used at the rate of 500 to 1,500 pounds to the acre, depending upon
the crop which is to follow the potato crop and the liberality of the
grower. The fertilizer may be applied broadcast if put on at the rate
of 1,000 pounds or more to the acre. When less than 1,000 pounds to the
acre are used it is almost universally applied along the line of the
row, a furrow being opened for the reception of the fertilizer; which
is scattered by hand or by a distributor which can be used to fertilize
several rows at a time. After the fertilizer has been distributed,
a cultivator is run along the line of the rows to incorporate the
fertilizer with the soil in order to prevent its coming in contact with
the seed when planted. Sometimes the furrow is refilled and reopened
prior to the planting of the seed, so as to incorporate the fertilizer
more completely with the soil. Still another plan is to open the
furrow, distribute about one-half the quantity of fertilizer to be
used in the bottom, incorporate it with the soil, plant the potatoes,
partially cover them, and scatter the remainder of the application on
the seed bed above the seed.
_Planting._--The rows should be laid off as close together as
practicable without interfering with horse cultivation. Generally
the seed pieces should be dropped in furrows made in the level field
and not on ridges. However, low ridges are advantageous for an early
crop and on poorly drained land. In covering the seed pieces, whether
they are planted flat or on ridges, it is well to leave a small,
sharp ridge marking the line of the row. In some localities, however,
where excessive moisture is not feared, the opening furrows are only
partially filled after planting, leaving a depression along the row to
be filled by the use of the smoothing harrow or other implement. In
planting late in the season this course is sometimes advisable. The
pieces may be dropped by hand in the open furrow, or a potato planter
may be used, dropping and covering the seed pieces at one operation.
There are several potato planters that do very satisfactory work, but
their cost restricts their use to those who plant a large acreage in
potatoes or to cases where several farmers can use one together. Their
more extended use is perhaps desirable, since they save a considerable
amount of labor and enable the potato grower to take full advantage of
even a brief period of favorable weather at planting time regardless of
scarcity of labor. In the preparation of the ground and in planting,
the earth along the line of the row should be compacted as little as
possible consistent with thorough work, and hence the team should be
made to walk between the rows whenever possible instead of along the
drill. There is a simple potato coverer constructed somewhat like a
triangular snowplow, with the wide end forward and a portion of the
point or apex cut away so as to leave a narrow opening at the rear. No
special implement, however, is required for this purpose.
_Planting Machines._--Planting potatoes by hand on any large scale is
out of the question on account of the expense. The large potato grower
can of course afford the most modern machinery. In a community of
small potato growers it is possible for them to own machinery jointly,
and thus avoid any large expense to the individual farmer. The two
most expensive machines connected with potato growing are the planter
and the digger. A word of caution about the type of planter is perhaps
desirable. There are some planters which pick up the seed potatoes
by means of a prong or fork which breaks the skin of the tuber. This
exposes the potato to any germs of potato diseases which may be present
in the soil. Furthermore, it carries any germ disease that may be on
some of the seed potatoes to others. There are planters which pick
up the potatoes in such a way as not to break the skin. This point
is especially important in planting whole seed. In planting cut seed
there is still the danger of transferring the disease from one piece
of potato to another. Whatever planter may be used, some one should
ride on the machine in order to see that it works regularly, so as to
give as nearly a perfect stand as possible. The improved planters of
today open the furrow, drop the seed, cover it, firm the dirt over the
seed, and mark the next furrow. Such a planter is drawn by two horses.
Experiments with potatoes planted in rows all the way from 36 to 42
inches apart indicate that the best distance depends upon the seasonal
conditions and type of soil; it is a problem for each grower to solve
for himself. The distance apart the potatoes should be planted in the
row also depends so much upon the variety, the fertility of the soil,
the availability of water, etc., that each farmer must determine this
from his own experience.
_Time of Planting._--Each community is the best judge of the proper
date for planting. Where potatoes are grown for the early market the
aim is to plant as early as possible, without subjecting the young
plants to severe cold. The crop should be planted at such a date as
to bring the stage of growth during which the tubers are rapidly
developing at a time when there is ordinarily an adequate supply of
moisture. The month when dry weather is most certain varies with the
locality, and each potato grower should so time his planting as to be
least affected by drought. Where the growing season is long the crop
that is to be stored over winter should be planted very late, so that
it may remain in the ground until cool weather. On the other hand,
where the season is short, late varieties should be planted in time to
ripen before frost.
_Depth of Planting._--The Toots of a young potato plant grow, not
directly from the seed piece, but from the underground joints or nodes
of the stem. From these underground nodes also grow the short stems
which bear the tubers at their extremities. Hence the seed pieces
should be placed deep enough in the soil to permit several of these
joints to form below the surface, so as to afford room for an ample
supply of roots and tuber-bearing stems to grow. Many experiments
have been made to ascertain the best depth for planting. The results,
with some exceptions, favor planting not less than 4 inches deep.
The favorable effects of deep planting were especially marked on
well-prepared, friable soil and in dry seasons. Very deep planting is
open to objection because of the increased labor of harvesting and the
danger of a deficient stand when weather conditions are unfavorable.
Very shallow planting reduces the yield and injures the quality of the
crop.
_Growing Seed Potatoes Under Mulch._--The Nebraska Experiment Station
reported an interesting comparison of the value for seed purposes of
potatoes grown under mulch with those grown with ordinary cultivation
under like conditions, which indicates that the mulch method offers a
convenient and practical means of producing good home-grown seeds under
Nebraska conditions. The theory of the method and the results obtained
in the comparative tests are thus stated: Potatoes are a cool-weather
crop. It is because of this that they succeed so well in the far north.
Moreover, potatoes require for their best development fairly uniform
conditions, especially as regards soil moisture and soil temperature.
This being the case, why should not potatoes grown under a litter
mulch be especially well developed and therefore make strong seed? The
soil beneath a mulch not only has a moderately low temperature during
summer, but its temperature is also exceptionally uniform, varying not
more than a degree or two between day and night and only a few degrees
from day to day. The soil moisture beneath a good mulch is also more
abundant and much more nearly uniform in amount than in case of bare
ground, even though the latter is given good tillage.
The value for seed purposes of tubers grown under a litter mulch has
been tested during two seasons at the experiment station. In 1904 a
plat of potatoes was mulched with straw and an adjoining plat was
given careful cultivation. The soil of the two plats was practically
uniform and the seed planted on the two plats was taken from the same
lot of tubers. Seed was saved from the mulched and cultivated plats
separately, kept under the same conditions during winter, planted on
adjoining plats in the spring of 1905, and given identical cultivation
during the summer. In 1906 the experiment was repeated with seed
grown in mulched and in cultivated ground the year before. The same
precautions were observed as in the first test. Uniform seed was used
to start with in 1905. The seed saved from the mulched and from the
cultivated plats was taken as it came, without selection, and was kept
over winter under the same conditions. Both kinds of seed were cut in
the same way, planted in the same way, on adjoining plats, and treated
alike as regards tillage, spraying, etc. Under these conditions any
constant differences in yield between the two plats must be ascribed to
the effect of the methods of culture employed the previous season. The
yields obtained from the mulched and from the cultivated seed were as
follows: Cultivated seed, 384 pounds in 1905; mulched seed, 563 pounds
in 1905; cultivated seed, 123 pounds in 1906; mulched seed, 174 pounds
in 1906.
The use of seed that had been grown under a mulch the preceding year
increased the yield of potatoes 47 per cent in 1905 and 41 per cent
in 1906. If further tests confirm the results reported here, it would
seem that mulching might be used for the production of high-grade seed
potatoes at home. Moreover, mulching usually results in increased
yields if properly handled. Mulching potatoes on a large scale is of
course impracticable, but most farmers could easily mulch enough of
their potato field to produce the seed that they would require the
following year, and in doing so they would not necessarily increase the
cost of production per bushel.
_Time to Cut Seed Potatoes._--At least three American experiment
stations have conducted tests to learn the effect of cutting seed
potatoes several days or weeks in advance of planting. The results
varied somewhat according to the length of time that the cut sets
remained unplanted, but on the whole indicated no marked difference
in productiveness between planting freshly cut pieces and those that
had been cut for a week or less. The investigations of Kraus and of
Wollny in Germany led to the conclusion that a slight wilting of the
seed pieces increased the yield on moist soils and in wet seasons, but
reduced it on soils not retentive of water and in dry seasons. On the
whole it appears that the storing of cut pieces for several days, which
sometimes becomes necessary, is attended with no great disadvantages.
Of course due care should be taken in such instances to prevent
heating, and it may be well to dust the cuttings with gypsum (land
plaster) to prevent excessive wilting.
_Seed End v. Stem End._--When potatoes are cut in half through their
smaller diameter there is a seed or bud end more or less crowded with
eyes and a stem or butt end on which there are few eyes. Experiments
to determine the relative values of cuttings from the stem end and
from the seed end of the tuber have been numerous. The majority of
these showed that the yield was greater when the seed end was used.
The superior productiveness of the seed end as compared with the stem
end was maintained, whether the halves of the potatoes, the thirds, or
smaller cuttings were employed.
_Effect of sprouting._--The growth of sprouts before planting is made
at the expense of the tubers from which they draw their support. Hence
if these shoots are rubbed off before planting there is a total loss of
the nutriment contained in them. Moreover, numerous weak shoots grow
from the injured eye. To prevent these evil consequences of premature
sprouting, seed potatoes are stored in a dark, dry, cool place.
In spite of all precautions the tubers sometimes sprout; but when
practicable only potatoes that have not sprouted should be selected for
planting. If the eyes appear dormant in spring, seed potatoes may be
exposed to the light and warmth for a few days before planting so as to
promote germination and prompt growth. If long exposed, sprouts will
form and careful cutting and planting by hand become necessary, so as
to avoid breaking of these sprouts.
_Quantity of Seed Potatoes per Acre._--A bushel of potatoes (60 pounds)
may contain 240 quarter-pound tubers. When the seed pieces are planted
a foot apart in 3-foot rows an acre requires 14,520 sets. When tubers
averaging 4 ounces are employed an acre requires at these distances
60 bushels for planting whole potatoes, 30 bushels when halves are
used, and 15 bushels when quarters are planted. In a number of tests
the amount of seed cut to 2 eyes, spaced 1 by 3 feet, averaged 13
bushels per acre, the usual range being from 10 to 14 bushels. In
18 experiments with many varieties the average amount of seed cut to
single eyes was at these distances 6.3 bushels per acre, the usual
range being from 5 to 7 bushels, though the varieties with large tubers
bearing few eyes required considerably more seed.
_Size of Seed Pieces._--In the size of the seed piece planted the
practice of different farmers varies widely, some advocating a liberal
use of seed and others claiming equally good results from small
cuttings. To aid in settling this question the State agricultural
experiment stations have made numerous tests of seed pieces of
different sizes. Taken separately these experiments show certain amount
of divergence in results, as might naturally be expected of tests
conducted under widely different conditions. However, the majority
of these tests, and especially the figures expressing the average
results of all available American experiments, may be safely taken
as indications of what the farmer, under ordinary conditions, will
generally, but not always obtain. The effect of size of seed pieces on
yield of crop will be treated here under three distinct heads: (1) On
the total yield; (2) on the gross yield of salable potatoes, and (3) on
the net yield of salable potatoes, i. e., after deducting the amount of
seed planted.
_Effect on Total Yield._--In making up the averages below it was found
practicable to use the results of 19 tests of single eyes _v._ 2-eye
pieces, 4 tests of 2-eye cuttings _v._ quarters, 17 comparisons of
quarters and halves, and 44 tests of halves _v._ whole potatoes. The
results of other experiments less completely reported were used for
the purpose of corroboration. The following table shows the _average_
results of these tests, including potatoes of all sizes:
Bushels. Per cent.
Excess from use of--
2-eye pieces over 1-eye pieces 26 21
Quarters over 2-eye pieces 15 16
Halves over quarters 24 18
Whole tubers over halves 31 18
If there are compared all the total yields with the total yield
produced by single eyes there appears an increase of 21 per cent for
2-eye pieces, 41 per cent for quarters, 67 per cent for halves, and 96
per cent for entire tubers. The total yield resulting from planting
whole potatoes is practically double that obtained by planting single
eyes. Thus far there is considered only the total yield, i. e., large
and small potatoes, and it is found that the total yield increases
somewhat uniformly as the size of the seed piece is increased. The
farmer and gardener, however, have to consider other factors than
the total yield, for a heavy crop may consist very largely of tubers
too small for the market, or the great expenditures for seed when
large pieces are planted may more than counterbalance the increased
yield. Before noting the gross and net yields of large or salable
tubers, resulting from seed pieces of different sizes, it is well to
consider the causes inducing a somewhat regular increase in total yield
accompanying the use of larger seed pieces.
Several causes operate to increase the yield when large seed pieces
are planted. The larger the cutting the greater generally the number
of eyes and the number of stalks. The young shoot, before it develops
a strong system of feeding roots, is dependent for nutriment on the
material stored up in the seed piece; hence the more abundant this
supply the more vigorous the growth of the plant and this increased
luxuriance is not confined to the early stages of growth, but is marked
throughout the growing season. Investigation has shown that severing
the connection between the seed piece and the growing vine, even after
the latter is thoroughly rooted, reduces the yield of potatoes. The
danger of partial or entire failure resulting from an imperfect stand
is much greater with small cuttings than with large seed pieces. The
small pieces with extensive cut surfaces are liable to perish should
the season be unfavorable, either through excessive moisture or
drought. The sprouts from small cuttings being weaker reach the surface
with difficulty, or fail entirely on soil not properly prepared.
_Effect on Gross Salable Yield._--By averaging the results of the
experiments referred to above, it is found that the actual increase in
the potatoes of salable size due to using larger seed pieces was as
follows, every increase in the size of the seed pieces being followed
by an increased gross salable yield:
Bushels. Per cent.
Excess from use of--
2-eye pieces over 1-eye pieces 23 21
Quarters over 2-eye pieces 10 15
Halves over quarters 15 15
Whole tubers over halves 14 10
_Effect on Net Salable Crop._--Before concluding that the largest seed
pieces are the most profitable it becomes necessary to deduct from
the crop the amount of seed planted. It is plain that the increased
amount of seed potatoes required when larger pieces are used may more
than counterbalance the increase in yield obtained. The true test of
profit is the market value of the crop produced, less the cost of
seed planted. Should the quantity of seed potatoes used be subtracted
from the total yield of large and small potatoes or from the salable
crop? If small or unsalable seed potatoes are planted, then the former
course is the proper one, but since large or medium tubers (either
entire or cut) are generally selected for seed purposes, it seems best
to subtract the seed from the salable crop, thus ascertaining the net
salable yield. The following table shows the actual average results
for the net salable yield; that is, the crop after deducting the small
potatoes and the seed used:
Bushels. Per cent.
Excess from use of--
2-eye pieces over 1-eye pieces 15.0 14
Quarters over 2-eye pieces 7.0 15
Halves over quarters 5.0 6
Halves over whole tubers 8.5 8
The amount of the net salable crop rose with the increase in the size
of the cutting employed, but when the whole potato was planted the
figures declined on account of the large amount of seed potatoes which
had to be deducted. The above figures indicate a very slight advantage
in planting halves rather than quarters when the price of seed and crop
produced are the same. As a matter of fact, spring prices are usually
somewhat higher than fall prices. A high price for seed potatoes may
make it profitable to plant smaller pieces (as, for example, quarters)
than would be economical where seed and crop command the same price per
bushel.
_Amount of Seed Potatoes._--In the following diagram 100 represents
the total yield from planting single eyes. The figures may be read as
bushels per acre, if it is constantly borne in mind that there are
being considered soils of such character as to average 100 bushels of
large and small potatoes per acre when planted with 1-eye pieces. The
first group answers the question, "What size of seed piece generally
affords the largest yield of large and small potatoes?" The second
group answers the query: "What size of seed piece generally gives the
greatest yield exclusive of small potatoes?" The third group offers an
answer to a still more important question: "What size of seed piece
generally produces the largest yield after deducting both the small
potatoes and the amount of seed planted?"
_Yield from planting different seed pieces, assuming 100 as the total
yield from single eyes._