EXTENSION COUESE IN SOILS. 51 
tained in the seed, the greater portion being left in the stalk or straw. 
Corn, potatoes, cabbage, and most truck crops require relatively 
large supplies, varying from 60 to 100 pounds per acre, depending on 
yield and somewhat on kind of plant. Tobacco, for instance, requires 
unusually large quantities of this element. The legumes, especially 
clover and alfalfa, which are used as hay, also contain large quan- 
tities, alfalfa frequently removing as high as 150 pounds of this ele- 
ment per acre in the 5 or 6 tons grown annually. Essentially all the 
potassium which truck crops and hay contain is removed from the 
farm when they are sold, while in the growing of cereals of which only 
the seed is usually sold, relatively small amounts of this element are 
lost from the farm. 
Soils needing 'potassium (Ref. No. 1, p. 197). — From the foregoing 
it is evident that potassium-bearing materials are especially needed 
under Ihe following conditions: (1) On muck and peat soils; (2) on 
upland soils low in potash and of coarse texture, such as sandy soils; 
and (3) in the growth of certain truck crops and of hay, which require 
unusually large quantities of this element. 
Potassium-Bearing materials (Kef. No. 7, pp. 278-287). — The most 
important sources of commercial potassium are the deposits of the 
Stassfurt region, in Germany. (Ref. Nos. 4, pp. 216-218; 5, pp. 529- 
531.) The potassium exists in various salts, so that the raw product as 
mined varies greatly in the amount of potassium contained. Some of 
these salts are used directly upon the soil where the distance of haul is 
not too great. Kainit, one of these salts containing from 9 to 10 per 
cent of potassium, is very largely used in Germany and is imported 
to some extent into this country. The salts of potassium used most 
as fertilizers in this country, both alone and in the manufacture of 
complete fertilizers, are potassium sulphate and potassium chlorid 
(muriate of potash). It has been generally held that the chlorin 
in the latter material is injurious to certain crops, especially to 
potatoes and tobacco, and for these crops the use of the sulphate is 
usually advised. 
The use of potassium salts. — When potassium salts must be de- 
pended upon to supply all or essentially all the potassium, from 100 
to 300 pounds of muriate of potash must be used annually. Such 
crops as potatoes, sugar beets, and cabbage require relatively larger 
supplies than grain. Larger quantities should be used on sandy, 
muck, or peat soils than on loam or clay-loam soils. The salts 
should be spread evenly and should be well worked into the soil. 
Where potatoes are to be grown the muriate should be applied the 
fall before or the sulphate of potash used in the spring. Heavy 
applications of muriate in the spring tend to roughen the skin of the 
potato. When a large part of the crops grown on the farm are fed 
