EXPERIMENTS WITH FALLOW IN MONTANA 3 
Table 1. — Monthly precipitation for April to August, inclusive, and the total 
annual precipitation, 1917 to 1923, inclusive 
Precipitation (inches) 
Year 
April 
May 
June 
July 
August 
Seasonal, 
April to 
August 
Annual 
1917 
0.86 
.44 
.31 
1.71 
.80 
1.43 
.78 
0.42 
.08 
1.09 
1.39 
2.83 
2.37 
1.93 
1.59 
1.51 
1.99 
2.20 
2.68 
.90 
4.86 
0.43 
.74 
.19 
1.36 
2.16 
1.90 
3.65 
0.70 
2.10 
.60 
1.26 
.53 
.92 
1.49 
4.00 
4.87 
4.18 
7.92 
9.00 
7.52 
12.71 
11.86 
1918 
8.55 
1919 ... 
7.56 
1920 
11.20 
1921. _. 
13.37 
1922 
10.26 
1923.. 
16.03 
7-year average 
.90 
1.44 
2.25 
1.49 
1.09 
7.17 
11.26 
EVAPORATION 
Daily measurements have been made of the evaporation from a 
free water surface during the months from April to September, 
inclusive. Several climatic conditions influence the total evapora- 
tion, including humidity, temperature, and wind velocity. The 
total amount of evaporation is a fair criterion of the climatic con- 
ditions, with the exception of precipitation, as affecting crop produc- 
tion. Table 2 shows the evaporation by months for the period from 
April to September, inclusive, and the total for the years from 1917 
to 1923, inclusive, with the 7-year average for each month and for 
the entire period. 
The average seasonal evaporation for the seven years was 36.182 
inches. The total evaporation for 1919 was the highest for the 
period. This was the year of lowest rainfall. The evaporation for 
1921 was almost as high as for 1919, although the rainfall during the 
growing season was nearly normal. The highest evaporation is in 
July, the average for this month being nearly 1 inch more than for 
either June or August, which are the next highest. The total for 
July was over 9 inches in 1917 and 1919. The evaporation for July 
and August was unusually low in 1923. 
Table 2. — Monthly evaporation for April to September, inclusive, 1917 to 1923, 
inclusive 
Evaporation (inches) 
Year 
April 
May 
June 
July 
August 
Septem- 
ber 
Total 
1917 
2.578 
4.678 
4.314 
2.374 
4.054 
2.783 
4.628 
5.533 
6.118 
6.460 
6.889 
5.294 
5.325 
6.648 
6.091 
8.390 
7.659 
6.795 
7.024 
6.936 
6.333 
9.518 
7.311 
9.440 
8.210 
8.734 
6.965 
5.827 
7.033 
6.291 
7.646 
7.744 
8.306 
7.229 
4.945 
3.885 
3.685 
4.461 
4.973 
4.890 
5.152 
4.124 
34. 638 
1918 
36. 473 
1919 
39. 980 
1920 
36. 985 
1921 
38. 302 
1922 
34. 390 
1923 
32. 505 
7-year average 
3.630 
6.038 
7.033 
8.001 
7.028 
4.453 
36. 182 
