HOW TO CONDUCT FIELD EXPERIMENTS 

 WITH FERTILIZERS. 



Water and its constituents hydrogen and oxygen, and carbon, 

 nitrogen, phosphoric acid, potash and lime are the chief compo- 

 nents of every crop that the farmer or the horticulturist produces. 

 If the quantity that the crop can get of any one of them is too 

 small for the making of a good yield, the yield will not be suf- 

 ficient no matter how much there may be of all the others. If the 

 quantity of any one of them is more than enough for a good yield, 

 it is only foolishness to supply any more of that substance in fer- 

 tilizers. The supply of water and its constituents, and of carbon, 

 are practically beyond the control of the crop-grower except in so 

 far as water may here and there be supplied by irrigation, or 

 may everywhere be conserved by shallow surface tillage properly 

 managed. The supply of lime is usually large enough in ordinary 

 arable soils. Therefore only nitrogen, phosphoric acid and potash 

 are left to be looked after ; these, as every consumer of commercial 

 fertilizers knows, are the things that he pays for in whatever of 

 these fertilizers he buys. 



By the introduction of leguminous plants, such as clover, vetch, 

 lupine, peas, beans and the like, into his rotations, he may save 

 himself from the necessity of buying so much nitrogen as he might 

 otherwise have to get in order to preserve the proper balance of 

 the plant-foods in his soils. These crops, as almost every farmer 

 knows, can get a part of their nitrogen from the air ; and they will 

 in general get more of it from the air and less from the soil the 

 poorer the soil is in available nitrogen, and the richer it is within 

 certain limits in potash and phosphoric acid. 



Every ordinary arable soil has far more than enough of nitro- 

 gen, phosphoric acid and potash for the production of a good 

 many crops ; and yet there are many such soils which will not 

 yield paying crops unless fertilized with one or more of these very 

 same plant-foods. 



It may be taken for granted that an acre of everjr such soil con- 

 tains in the uppermost twelve inches at least 5,600 lbs. of nitro- 



