Mar, 17,1923 Influence of Soil Temperature on Seedling-Blight 859 
namely, temperature. That is, wheat blights in a comparatively warm 
soil above 12 0 C., whereas, on the other hand, corn blights in a cool 
soil below 20° to 24 0 . Inasmuch as certain of these factors, especially 
temperature and moisture, play an important r 61 e in forming the field 
environment for both wheat and com seedlings, a series of periodic 
field sowings were made at Madison, Wis., during the spring and fall 
of 1920 and the spring of 1921. These should point toward possible 
remedial measures for this and similar seedling diseases of the cereal 
crops as well as check against the greenhouse results. 
A uniform plot of land was prepared for the spring sowings in the 
previous fall and reworked at the earliest possible date in the spring. 
It has happened in the past two years that early in March the soil has 
warmed and dried sufficiently to permit the installation of the thermo¬ 
graphs and electrical resistance 
thermometer bulbs to obtain soil- 
temperature readings and to sow 
the first wheat. Following this 
the temperatures have gone down 
again during the remainder of 
March and most of April. It 
has been possible in this way, by 
watching the daily soil temper¬ 
ature and moisture, to make 
seedings at different intervals, 
especially a few days after a 
rain when moisture was well 
within the limits of plant re¬ 
sponse (fig. 2), which would 
throw the germination period 
of the grain at soil temperatures 
below or above the critical tem¬ 
peratures for seedling-blight. By 
this method it has been possible to check the constant soil-temperature 
studies in the greenhouse with fluctuating field temperatures. 
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- 7 
§ 
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V 
JO Gs 
23 9 
20 y 
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Fig. 10. —Graph showing relation of date of seeding to 
the development of seedling-blight of Marquis wheat 
in 1920. No blight occurred in the cool soil during 
March and April when the mean soil temperature was 
below is* C. On the other hand, abundant blight 
developed in the later seedings. May x and xo, until 
the high soil temperatures of June inhibited the devel¬ 
opment of the parasite. (Suxnmary of fig. xx.) 
RELATION of date of seeding to the DEVELOPMENT OF SEEDLING- 
BLIGHT IN MARQUIS WHEAT 
EXPERIMENT IN 1920 
Two sowings were made on March 31 and April 22, which germinated 
before the average mean soil temperature was above 12 0 C. Following 
this, two sowings were made on May 1 and 10, which germinated with an 
average mean soil temperature between 12 0 and 15 0 . Finally, a sowing 
was made on June 9, during a period when the average mean soil tem¬ 
perature was about 26°, and the maximum running up to 36° for several 
hours during the middle of the day. Each sowing of these different 
periodic series consisted of 10 rod rows for control and inoculated seed 
and 5 rod rows for scabbed seed. The duration of the germination 
period, the percentage stand of disease-free plants, and the average mean 
temperatures are given in Tables IX and X and shown graphically in 
figure 10. The mean daily and daily maximum soil temperatures 4 
inches below the surface and mean daily air temperatures 6 inches above 
the soil, together with the percentages of healthy plants in the different 
seedings, are given in figure 11. 
