210 
Journal of Agricultural Research 
Vol. XXVI, No. 5 
Tabl,E VII .—Results of an experiment with Harvest Queen wheat, combining a study of 
soil moisture and soil temperature (fifth series), in loam soil having a moisture-holding 
capacity of 67 per cent , using culture 392 on seed sown May 4,1922, experiment ending 
May 26 1 1922, at Madison, Wis. 
Experiment 3. 
Soil moisture, on basis of moisture-holding capacity. 
Soil 
tempera¬ 
ture. 
37.3 per cent. 
46.2 per cent. 
55.2 per cent. 
62.6 per cent. 
Number 
Infection 
Number 
Infection 
Number 
Infection 
Number 
Infection 
of plants. 
rating. 
of plants. 
rating. 
of plants. 
rating. 
of plants. 
rating. 
°c . 
12 
59 
8-3 
59 
16.8 
53 
14-3 
55 
18.6 
l6 
60 
18. 5 
57 
32. 8 
60 
10. 0 
58 
15.6 
20 
53 
3 2 -3 
60 
53-7 
55 
66. 6 
55 
45 - 6 
24 
58 
20.4 
57 
60. 6 
5 1 
73-8 
59 
80. 7 
28 
60 
35-4 
53 
74. 8 
58 
82. 7 
56 
86.3 
32 
58 
9.8 
56 
8.9 
59 
32. 2 
59 
42.3 
34-5 
54 
8.0 
S8 
7-3 
53 
i 5 -o 
45 
3 - 7 
RESULTS 
Tables VI and VII and figures 3 and 4 give the results of the ioil 
moisture experiments. In general all of the data thus far obtained 
indicate that relatively high soil moistures favor the Helminthosporium 
disease of wheat. It is 
70 r 
1 
r 
'222 
of interest to note the 
joint influence of soil 
temperature and mois¬ 
ture in experiment 3 as 
shown in Table VII and 
figures 4 and 5. In fig¬ 
ure 5 it will be noted 
that the temperature 
optimum for disease 
development remained 
constant at all the soil 
moistures. Reference 
to figure 4, however, 
will show that the soil 
moisture optima were 
shifted when the soil 
temperature was 
changed, the higher 
temperatures enabling 
the highest moistures to produce the maximum quantity of disease. The 
results indicate that the moisture optimum tends to drop in percentage 
as the soil temperature lowers. The irregularities in the low moisture curve 
in figure 5 and those in the 12 0 and 34.5 0 C. curves in figure 4 are not con¬ 
sidered significant, since these curves represent the unfavorable extremes 
of the factors under study. Slight irregularities in other factors un¬ 
doubtedly register themselves in a more pronounced manner when unfa¬ 
vorable soil moistures and temperatures are maintained, thus making it 
difficult to get the true expression of the influences of these two latter factors. 
333 44.4 55.6 666 
PERCENTAGE OP MO/STOPE HOIP/NG 
CAPAC/TP OP SO/L 
Fig. 3.—Graph showing the amounts of Helminthosporium infection 
on the subterranean parts of wheat seedlings grown at different 
soil moistures with other factors as uniform as possible, in experi¬ 
ments 1 and 2. Tabular results are given in Table VI. 
