Studies oe Hkaetii in Potatoes. 
5 
the-large is regarded as of most value. These studies will be pre¬ 
sented under the following heads : 
I. Studies of soil temperatures. 
II. Studies of potato roots and the potato leaf. 
III. Greenhouse studies of the effect of various soil temper¬ 
atures and percentages of moisture upon potato plants. 
IV. Field studies of heat and soakage, and temperatures of 
soil and of irrigation water. 
V. History and practices of potato-growing districts. 
VI. The hope and the great difficulty of attempting to secure 
disease-resistant potatoes. 
VII. Summary of what we know of the conditions for potato 
health and permanent potato production. 
T. STITDIES of soil TEMPERATURES. 
It was desired to know whether soil temperatures vary greatly 
in different seasons. The Colorado Station at that time had no 
soil temperature records but we had recourse to the very complete 
records kept by the Nebraska Station, and selected for comparison 
with each other the temperatures at Lincoln for known good years 
and known years of poor production. Certain of these are sum¬ 
marized below: 
MEAN SOIL TEMPERATURES AT DIFFERENT DEPTHS. 
(Taken at the Agricultural Experiment Station, at Lincoln, Nebraska, for May. 
June, July, and August 
of 1894 
and 1901, dry hot 
years. 
and for the same 
months of 1897 
and 1902, 
years of average 
weather and good 
moisture 
supply.) 
1 
3 
6 
9 
12 
24 
36 
inch 
inches 
inches 
inches 
inches 
inches 
inches 
1894 
(Dry year) 
May . 
. 63.3 
72.7 
68.6 
66.8 
64.7 
59.2 
59.0 
June . 
. 78.4 
40.1 
75.6 
73.7 
71.5 
65.7 
62.6 
July . 
. 86.9 
87.6 
82.2 
80.0 
77.9 
72.5 
68.8 
August . 
. 88.7 
89.2 
83.0 
81.1 
79.8 
Vb.3 
72.2 
1897 
(Good year) 
May . 
62.4 
61.1 
.57.7 
5 4.4 
52.3 
June . 
. 76.9 
69.7 
71.1 
65.9 
61.5 
58.6 
July . 
. 81..6 
82.8 
81.1 
74.7 
68.7 
66.2 
August . 
. 84.4 
80.5 
79.3 
73.9 
70.7 
68.7 
1901 
(Dry year) 
May . 
. 76.3 
75.4 
71.6 
66.8 
62.4 
56.6 
53.2 
June . 
. 89.6 
88.5 
84.0 
77.6 
72.5 
65.1 
60.8 
July . 
.107.3 
102.2 
95.3 
87.3 
81.9 
74.1 
69.3 
August . 
92.2 
88.4 
82.3 
78.4 
73.7 
70.9 
1902 
(Good year) 
May . 
. 75.2 
74.6 
71.9 
67.4 
63.4 
57.6 
54.5 
.Tune . 
. 75.3 
74.3 
72.4 
70.2 
67.4 
63.7 
61.5 
July . 
. 82.0 
81.8 
78.6 
, 75.6 
73.2 
68.7 
66.1 
August . 
. 79.1 
79.3 
77.8 
74.8 
73.1 
70.8 
68.9 
The above records are sufficient to show that drouth is not the 
only injurious factor in the dry years but that soil temperature may 
reach an iniurious point in such years. If the temperature for July 
