HNTS ON SOILS AND FERTILIZERS 45 
centage of phosphorus. This is very slowly 
available, and results from this source cannot 
be noticed for a year or two after it has been 
applied. However, it is much cheaper in cost, 
and many farmers follow the practice of mix¬ 
ing some of this with every load of manure 
that is spread on the land, thereby making 
the spreading of this form a simple matter. 
Steamed bone meal, finely ground up, offers 
another source of commercial phosphorus. 
This is a by-product from the large packing 
plants and after the bones are steamed at 
these plants, they are ground up, and sold 
out, especially to truck gardeners, for phos¬ 
phorus fertilizer. This form is usually applied 
at the rate of 200 to 300 pounds per acre. 
Potash fertilizers have in the past been 
largely supplied from the Stassfurt mines of 
Germany. This is a large potash salt deposit, 
and these mines alone have supplied a good 
share of the world’s potash in the past. The 
chief combinations of this fertilizer in com¬ 
mercial form are sulphate of potash, muriate 
of potash and kainit. These are various forms 
of Stassfurt potash salts, and are all soluble 
in water. Unleached wood ashes also contain 
a fair amount of potash, especially hardwood 
ashes burned at a comparatively low heat. If 
these ashes have been exposed to the rains, 
however, they are of. little value as fertilizers. 
In our previous study of the test plots (see 
page 23) we found that we could determine by 
that method just what a certain piece of land 
needed by way of fertilizers. Often a farmer 
finds that he gets best reults by applying what 
