6 BULLETIN 881, U. S. DEPARTMENT OF AGRICULTURE. 
At Belle Fourche the yield of potatoes, large and small, for the 48 
plat years has averaged 135 bushels per acre, while the mean annual 
difference resulting from the growing of alfalfa has been a decrease 
of 4 ±6. The yield of marketable potatoes from the same plats has 
averaged 107 bushels per acre, with a mean annual decrease for the 
plats following alfalfa of 4 ±5.6. The percentage of the total yield 
Massed as marketable for the 48 plats is 81, with a mean annual 
difference in favor of the plats following alfalfa of 0.5 ±2.2. These 
results jndicate that at Belle Fourche there has not been, so far, any 
beneficial effect from alfalfa on subsequent yields of potatoes. 
At Huntley the total yield of potatoes for the 48 plat years has 
averaged 258 bushels per acre, while the mean annual difference in 
favor of the plats following alfalfa is 50 ± 12.6. The yield of market- 
able potatoes from the same plats has averaged 241 bushels per acre, 
with a mean annual difference in favor of the plats following alfalfa of 
55 ±11.4. The percentage of the total crop classed as marketable 
is 93, with the difference in favor of the plats following alfalfa of 
1±0.55. Thus, the results from the Huntley station indicate that 
the beneficial effect of alfalfa on subsequent potato crops, though 
fairly large, is, when judged by the size of the probable error, barely 
significant. 
In an earlier paper, the effects of farm manure on the crop yields 
in certain of these irrigated rotations was reported, 1 and it seems 
proper to present here a comparison between the effects of periodical 
applications of farm manure and the use of alfalfa in the rotation. 
Such a comparison of results appears to be justified, because the 
two tests were made in the same fields and the same set of plats were 
used as checks in both cases. The experiments reported for the 
test of farm manure covered the 6-year period from 1912 to 1917, 
while those of alfalfa covered the 6-year period from 1913 to 1918. 
There were, however, only three rotation pairs for the potato ex- 
periments with manure, while there were four pairs with alfalfa. 
Also, in the manure experiments the manure was applied immedi- 
ately preceding the potato crop in two of the three cases and to the 
sugar-beet crop, which preceded the potatoes, in the third case. In 
the alfalfa experiments the potato crop followed the alfalfa in all 
four cases. 
The comparative features of the two experiments are summarized 
in Table II. 
The results brought together in Table II show clearly that on the 
lighter soil of the Scottsbluff station both manure and alfalfa have a 
beneficial effect on the yield of potatoes. The manure has resulted 
in an increased total yield of the treated plats over that of the check 
i Scofield, C. S. Loc. cit. 
