FERTILIZERS. 113 



The table is very interesting and instructive, and will 

 bear a good deal of studying. Notice how many sub- 

 stances, in their percentages of nitrogen, potash, and phos- 

 phoric acid, approach in value stable manure. Notice that 

 the humus-making capacity (the organic matter) of dry 

 muck is three times as great as in stable manure. To 

 make the potash and lime in oyster-shells and mollusks 

 available for plant-food, they must be burnt. In marine 

 mud it is probably the nitrogen and alumina only that are 

 available ; the mineral matter, mostly fragments of shells, 

 being insoluble. As a rule, the per cent of organic matter 

 in the several substances is a measure of their humus-mak- 

 ing capacity. Note that all the substances that are the 

 product of combustion contain no nitrogen : combustion 

 destroys nitrogen. 



Corn-cobs, as will be seen, are amazingly rich in potash ; 

 but the quantity of ashes from them is amazingly small. 

 The potash in the ashes from a bushel of cobs is worth a 

 little scant of one-third of a cent. Note that decayed vege- 

 table matter, in its various forms, is much the same in the 

 proportions of the three elements. 



Let us bear in mind that the nitrogen in the different 

 substances varies greatly in its value, depending on its 

 availability : for instance, that in horn, hoof, and hair is 

 worth not over ten cents per pound, while that from blood, 

 castor-pomace, and cotton-seed meal is worth not far from 

 eighteen cents. Note that there is no potash in the lime 

 manures, phosphates, and phosphatic guanos. 



The following table is copied from an excellent little 

 pamphlet on the cultivation of potatoes, issued by the 

 Mapes Formula Company, 158 Friend Street, New York. 

 It shows the value of the plant-food taken out of the soil 

 by various crops. It is very valuable to us farmers, by 

 enabling us to determine whether or not we are increas- 



