EFFECT OF FALL IRRIGATION ON CROP YIELDS. 
The figures in Table IV show that in 1914 the yields of wheat, 
barley, and corn were higher on the fall-irrigated plats than on the 
check plats, the increases being 37, 2, and 1 per cent, respectively, 
while the yields of the four other crops were lower on the fall-irrigated 
land, and that the average yield increase of the seven crops in that 
year was 2 per cent in favor of fall irrigation. In 1915 the yields of 
all the crops were lower on the fall-irrigated land, the average decrease 
being 11 per cent. In 1916 all the crops yielded less on the fall- 
irrigated plats than on the checks, except potatoes, which yielded 5 per 
cent more. In the 3 -year average, wheat on fall-irrigated land showed 
an increase of 10 per cent, while all the other crops showed decreases 
ranging from 3 to 10 per cent, the average yield decrease of the seven 
crops on fall-irrigated land for the 3-year period being 4 per cent of 
the average yield of the check plats. 
The fact that of the 42 duplicate plat averages secured in the 3-year 
period only four were in favor of fall irrigation would support a pre- 
sumption that fall irrigation on this soil was detrimental. However, 
since not all the yields were against fall irrigation, it is possible that, 
the yield variations were accidental. In order to determine whether 
these differences were significant, the probable errors of the average 
yields have been calculated. The results are shown in Table V, in 
which the yields secured during the 3-year period are summarized. 
Table V. — Summary of the yields secured in the fall-irrigation experiments at the Belle 
Fourche Experiment Farm in 1914, 1915, and 1916, showing the probable errors of the 
averages. 
Unit of 
yield. 
Fall-irrigated plats. 
Check plats. 
Crop. 
Num- 
ber of 
plats 
aver- 
aged. 
Average 
yield per 
acre. 
Num- 
ber of 
plats 
aver- 
aged. 
Average 
yield per 
acre. 
Difference 
in favor 
of fall 
irrigation. 
Wheat 
6 
6 
6 
6 
6 
6 
6 
22. 1± 2.2 
61. 9± 5.0 
33. 9± 1.5 
13. 7± 1.4 
42. 2± 3.3 
8.4± 1.1 
167 ±23.0 
6 
6 
6 
6 
6 
6 
6 
20. 1± 1.4 
67. 8± 6.0 
36. 1± 2.5 
15. 2± .9 
43. 9± 3.1 
9.2± 1.1 
172 ±19.0 
+2.0± 2.6 
Oats 
Barlev 
Flax." 
Corn 
Beets 
Potatoes 
...do 
...do 
...do 
...do 
Tons 
Bushels... 
-5.9± 7.8 
-2.2± 2.9 
-1.5± 1.7 
-1.7± 4.5 
— .8± 1.5 
-5.0±30.0 
The figures in the last column in Table V show for each of the seven 
crops the difference between the average yield of the fall-irrigated 
plats and that of the check plats during the 3-year period. None of 
the differences was as great as the probable error, so that all must 
be regarded as insignificant. A similar tabulation of the yields of 
straw and stover (which are not shown here) produces a like result, 
there being no significant differences in the average yields of these 
products. 
The explanation of the somewhat lower average yields secured on 
the fall-irrigated land lies in the relatively low productivity of Series 
