PRINCIPLES OF MANURING. 47 



These figures are given onl}- as approximations, but they serve 

 to show in a gen(>ral way the amounts of the valuabU; ingredients 

 that an acre of ditferent kinds of farm produce woukl make use of; 

 also the rehitive quantities tliat different crops extract from the soil. 

 While studying tiiese tables it should be remembered that the com- 

 position of our farm crops varies according to the climate, season and 

 manner of manuring the soil. Well fertilized soil produces crops 

 richer in these essential ingredients, than will that whicli is poor and 

 unmanured. It must also be borne in mind that the amount of any 

 substance that a plant takes up is not a measure of the didiculty 

 with which it obtains the material. For instance, an acre of land 

 would need to contain more available niti'ogen in order for thirty 

 bushels of wheat to be grown, using about fifty-nine pounds of 

 nitrogen, than would be necessar}' for the growth ot two tons 

 of clover hay, using nearly ninety pounds of nitrogen. In other 

 words, clover can gather nitrogen more easily than wheat. The 

 table shows very plainly that different crops would exhaust the land 

 very differently. Twent}' tons of beets contain over four times as 

 much potash as sevent^'-five bushels of corn, but not very much more 

 phosi)horic acid. Like beets, potatoes and clover ha}' use a large 

 relative amount of potash. But we shall have occasion to note the 

 special needs of different crops later. 



A stud}' of the first table reveals one fact of great moment to the 

 farmer. It is plainly' shown that it makes a great difference as to 

 the form in which a farmer sells his surplus productions, if he would 

 harvest the resources of his land. In selling an ox weighing one 

 ton, only as much nitrogen is sent from the farm as would be lost 

 bj' selling about one and one-half tons of English hay. Of phos- 

 phoric acid, such an animal represents an amount found in less than 

 five tons of hay, while an eighth of a ton of hay would furnish the 

 ox with all the potash he has in his body. If the ftirmer were to 

 sell the hay and grain necessary to use in the production of two 

 thousand pounds of live animal weight, he would send from his 

 farm vastly more of those substances that have a manurial value 

 than if the animals had been grown and the manure returned to the 

 land from which the hay or grain was taken. It will be seen 

 later, that when food passes through an animal, only a small portion 

 of its nitrogen, phosphoric acid and potash is retained, while a larger 

 part of these substances passes into the manure. Unless a farmer 

 buys manure, the method of farming surest to retain or increase 



