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 2321
Quarters over 2-eye pieces 1015
Halves over quarters 1515
Whole tubers over halves 1410

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 15.014
Quarters over 2-eye pieces 7.015
Halves over quarters 5.06
Halves over whole tubers 8.58