24 CIRCULAR NO. 115, BUREAU OF PLANT INDUSTRY. 
nent sod is established, the banks become covered with Russian 
thistles, buffalo bur (Solanum vostratum), wild oats, sweet clover, 
and other troublesome weeds. The seeds of these weeds are freely 
carried by the canal water and are scattered far and wide over the 
fields. The resulting growth of weeds greatly increases the expense 
and labor of cultivation. It is practically impossible to produce 
pure seed crops of grain and alfalfa if weeds are allowed to multiply 
along the banks of canals and ditches which cut through the fields. 
The best check to the growth of weeds is a good grass sod. 
Another advantage of the grass covering is to furnish pasturage 
for live stock. The area occupied by ditch banks can not be util- 
ized for the production of cultivated crops, but can be made to 
vield some return when used for grazing. On many of the larger 
farms the aggregate area that may be made use of in this way is 
considerable. A half mile of canal bank of medium size has an 
area of 1 to 2 acres. Moisture is usually abundant on the lower 
slope of the banks, and a good growth of grass can be secured, which 
will furnish a fair return for the trouble and expense of seeding. 
! NATURE OF THE SOIL. 
The soils of the Bellefourche Project are of two principal types. 
In the northern part of the area the soils are mostly of the heavy 
clay loam, known locally as “ gumbo.” These soils are formed by the 
weathering of the Pierre shale which underlies the whole area. In 
the southern part of the project the soils are somewhat lighter on 
account of the silt and sand which they contain. The unweathered 
shale which is turned up in many places in building the canal banks 
is very unfavorable for the growth of grasses, but after a year or 
two of weathering it is possible to get grass started even in the partly 
decomposed shale. 
OBSTACLES TO SECURING A STAND. 
Alkali salts are present, although usually in small quantity, in 
many of the soils of the project. Over the greater part of the area, 
especially north of the Belle Fourche River, the alkali content ranges 
from 0.2 to 0.6 of 1 per cent in the first 6 feet of soil. South of 
the river there is generally less than 0.2 of 1 per cent. The alkali 
is of a relatively harmless type, consisting mostly of sulphates 
of calcium, magnesium, and sodium. Fortunately no black alkali 
(sodium carbonate) is present. Alkali is especially hkely to accumu- 
inate along ditch banks because of the high water content of the 
soil and the high rate of evaporation from the joose surface. This 
accumulation is especially noticeable in large fills, for in such places 
some water often seeps through the canal banks. Wherever more 
[Cir. 115] 
