EXTENSION COUESE IN SOILS. 51 



tained in the seed, the greater portion being left in the stalk or straw. 

 Com, 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 the 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-hearing materials (Ref. 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 fertihzers, 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 miiriate should be apphed 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 



