NORTHERN GREAT PLAINS FIELD STATION, 1913-1922 47 
More than 30 varieties of potatoes have been tested, some but a 
single year and others for varying lengths of time up to 10 years. 
Uninterrupted yields were obtained from three varieties for the 10 
years, 1913-1922, inclusive. During this period Green Mountain 
averaged 185 bushels, Irish Cobbler 163 bushels, and Rural New 
Yorker 144 bushels, per acre. Green Mountain was the highest yield- 
ing variety in the tests in 1913, 1914, and 1921. Of those varieties 
that have outyielded Green Mountain more than once, Pink Eye had 
the higher yield three times in the nine years that both were grown; 
Trish Cobbler and Rural New Yorker each exceeded it twice in 10 
years; Early Ohio exceeded it once in 9 years; and Karly Acme and 
Blue Victor twice each in 8 years. 
Various tests have been made in which the same. variety was 
erown from seed from different sources, and wide differences have 
been noted in the yields. The results show a tendency of home- 
srown seed to run out or degenerate. This factor greatly interferes 
with the accuracy and interpretation of variety trials. The prob- 
lem of keeping potatoes vigorous, and free from disease and degen- 
erate types, appears to be one of great importance here. 
Experiments to determine the best distance to space hills of pota- 
toes in the row have been conducted each year except 1915. From 
three to nine varieties have been under trial each year at different 
spacings, ranging from 14 to 30 inches. The average yields favor 
the closer spacing, but the higher yield from the closer spacing was 
sometimes obtained at the expense of quality and size. On the 
whole, the 20-inch spacing has been the most desirable. 
Considerable selection work with potatoes has been done, start- 
ing with the fall of 1914. The method first employed was to select 
superior hills of all varieties in the field at digging time and test the 
selections in bulk in comparison with the parent stocks. 
Starting with 1918 the selections were made on an individual-hill 
basis, with the number of varieties reduced to four, viz: Early 
Ohio, Irish Cobbler, Rural New Yorker, and Pink Eye. The best 10 
hills of each of these varieties were selected and the progeny of each 
hill kept separate. 
Starting with 1921 the tuber-unit method was used; that is, the 
progeny of each tuber was kept separate and selections were made 
of the best tuber units. This latter method is still being used with 
several standard varieties of potatoes. 
Results to the present time from the selections have been largely 
negative, in that no higher yielding strains have been isolated. 
AGRONOMIC INVESTIGATIONS ° 
ROTATION AND TILLAGE EXPERIMENTS 
The rotation and tillage experiments occupy two fields, known as 
the main field and the south field. The soil of the main field is a 
comparatively light sandy loam containing about 10 per cent of 
clay in the surface foot. The soil of the south field is much heavier, 
containing about 25 per cent of clay in the surface foot. This field 
slopes to some extent and is subject to run-off, both on it and from 
® By J. T. Sarvis, Associate Agronomist, and J. C. Thysell, Assistant Agronomist, Office of Dry-Land 
Agriculture Investigations. 
