122 AGRICULTURE 



many state laws require that the guaranteed analysis, or formula, 

 of a fertilizer shall be placed on the bag containing it. At the pre- 

 vailing prices of unmixed materials, a pound of nitrogen is worth 

 about sixteen cents, a pound of potash about five, and a pound of 

 phosphoric acid about four and a half. If a farmer understands 

 a fertilizer formula, he can tell how many pounds of each he is 

 getting in available form ; by the price of the ton he can tell whether 

 or not he is paying a reasonable price, including the manufacturer's 

 profit for mixing and bagging. If he be not willing to take time 

 and trouble to learn the A B C of the matter, his purse, and often 

 his crop also, will suffer. 



A few years ago a ' natural plant food ' was widely advertised 

 and extensively sold at from twenty-five to twenty-eight dollars the 

 ton. So much of the plant food which it contained was in insoluble 

 and unavailable forms that the real value of the mixture was one 

 dollar and fifty- two cents the ton. The printed formula was given 

 on the bag, as required by law. But to the man who did not under- 

 stand it, this was of no more value than so many Greek letters. 



EXERCISE 



1. To find out if land is acid, take some soil from two to four inches 

 below the surface and moisten it thoroughly. Put in it a slip of blue 

 litmus paper and leave it there several hours. If the blue paper turns 

 red, the soil is acid and needs lime. 



2. Lay off eight plots and make the field tests described on page 120. 

 Remember that weather will affect the results; the experiment should 

 be repeated several times. You may modify the experiment by using 

 more or less of certain substances, so as to" learn how to attain most 

 economically the best result for a given crop. 



3. Are commercial fertilizers used in your locality ? For what pur- 

 poses ? 



4. Get samples of different commercial fertilizers and test them, 

 comparing results on same soil with same crop plant. 



