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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._
RELATIVE TOTAL YIELD.
1 eye...........| 100 |______________
2 eyes..........| 121 |____________________
Quarters........| 141 |____________________________
Halves..........| 167 |____________________________________
Wholes..........| 196 |___________________________________________
RELATIVE GROSS SALABLE YIELD.
1 eye...........| 87 |_____________
2 eyes..........| 105 |___________________
Quarters........| 123 |___________________________
Halves..........| 142 |_____________________________________
Wholes..........| 157 |_____________________________________________
RELATIVE NET SALABLE YIELD.
1 eye...........| 83 |______________
2 eyes..........| 95 |___________________
Quarters........| 109 |______________________
Halves..........| 115 |___________________________
Wholes..........| 107 |_____________________
Taking as the correct measure of profit the yield of salable potatoes
less the amount of seed used, there is seen by the third section of the
diagram that with seed and crop at the same price per bushel it was
more profitable in these tests to plant halves than smaller cuttings
and whole potatoes. If there be taken account of the yield of small
potatoes the advantage of large seed pieces is even greater than the
figures in the last section of the diagram would indicate, for the
yield of small potatoes is greater with large than with small seed
pieces. Where large quantities of small potatoes can be profitably
utilized, as, for example, as seed for the second crop, the potato
planter may therefore use quite large seed pieces with advantage. On
the other hand, the higher price of potatoes in spring rather than in
fall is an argument in favor of planting quarters rather than halves
or whole tubers. A number of investigators have noted that large seed
pieces (either large cuttings or entire potatoes) afford an earlier
crop than very small cuttings, a matter of much interest to growers of
early potatoes. However, some growers have reported that uncut potatoes
germinate more slowly than large cuttings. Most of those who raise
potatoes for the early market use large cuttings rather than whole
potatoes.
In this connection it may be said that the seed-end half gives an
earlier crop than the other half. This suggests the expediency of
cutting a potato lengthwise when halves or quarters are to be planted,
thus securing on each piece one or more of the eyes which germinate
first. Another advantage of cutting lengthwise is that it insures a
more even distribution of the eyes on the several pieces. Of course
this system is not practicable when very small cuttings are to be made
from long, slender potatoes, since the large amount of exposed surface
would render the long pieces susceptible to injury both from moisture
and dryness.
If it is desired to cut the potato into small pieces the operator
should begin at the stem end, and the pieces should be cut in a compact
shape, and of as nearly equal size as is practicable without leaving
any piece entirely devoid of eyes. There are special implements for
cutting potatoes, and their use is reported as enabling a man to cut
four or five times as many bushels of seed per day as by hand. The
character of the work is said to be satisfactory. No definite rule can
be given as to the best size of seed piece, for this depends somewhat
on the distance between the hills and on the character of the soil and
season. Another important factor in determining the proper amount of
seed is variety. Some varieties are able to produce a crop almost as
large from small cuttings as from large pieces.
_Size of Seed Tubers._--A study of more than a hundred experiments
testing the relative values of large, medium, and small uncut tubers
confirms the general law that an increase in the weight of seed planted
affords an increase in the total crop. The yield of salable potatoes
increases less rapidly than the total yield. With whole potatoes as
seed the salable yield reached its extreme upward limit in one test
when tubers weighing about half a pound were planted; in another when
those weighing 4-1/2 ounces were employed. The limit of profitable
increase was reached with tubers weighing 4-1/2 and 3 ounces
respectively. The size of seed tubers selected becomes a matter of
importance when they are to be cut, for we have seen that the heavier
the cutting the larger the total yield, and seed tubers for cutting
should be of such size that their halves, quarters, or other divisions
shall not be extremely small.
_Small Potatoes for Planting._--Whether or not to use uncut small
potatoes for seed is an important question on which farmers are
divided. Some present the plausible argument that the use of undersized
potatoes results in degeneration. If this claim is based on the results
of experience it should determine practice, but if the conclusion is
simply a generalization based on the fact that large seed usually give
best results the reasoning is defective, and the question remains
open. The potato tuber is not a seed, but an underground stem, and the
relations existing between seeds and their progeny do not necessarily
exist between a tuber and its descendants. Others hold that potatoes
just below marketable size, if shapely and sufficiently mature, may be
used without serious deterioration, and that for economic reasons their
use is especially desirable, because if not planted or used at home
they must be lost or fed to stock, for which purpose their value is
usually smaller than the market price.
The result of tests at a number of experiment stations have uniformly
indicated that small tubers uncut can be used for seed purposes without
detriment to the succeeding crop. It may still be urged, however, that
the choice of small seed year after year will result in degeneration.
On this question the information is meager, but two experiments,
extending over four and eight years, respectively, have been reported
in which no degeneration resulting from the continued use of small
potatoes from the preceding crop was apparent. Although the evidence
seems fairly conclusive that small uncut seed potatoes may sometimes
be used with profit, it cannot be advised that small seed tubers be
selected year after year from a crop which has been grown from small
potatoes. Potatoes of irregular shape and injured tubers should be
rejected as unfit for planting.
_Number of Eyes and Weight per Set._--Many potato growers cut tubers
into pieces containing one, two, or more eyes, laying greater stress
on the number of eyes than on the size of the cutting. Extensive
experiments at the Indiana station and elsewhere prove that of the two
factors, number of eyes and weight of piece, the latter is the more
important. Of course it is desirable that each piece, whether large
or small, should contain at least one eye, and it has been generally
profitable for it to be of such size as to contain at least several
eyes; but whether it has one or many eyes it is important that the seed
piece be heavy enough to furnish abundant nutriment to the shoots which
spring from it. A single eye may give rise to several stalks, for each
eye is a compound bud or cluster of buds. An eye can be bisected, and
each half may then grow successfully if it is not a victim to dryness
or decay, to which its exposed condition subjects it.
In one series of experiments it was found that the number of stalks
growing in a hill was less dependent on the number of eyes than on
the size of the seed piece, whether cut or entire. In general, as the
number of eyes per piece increased each eye became less prolific in
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