86 AGRICULTURE. 



"make his farm an experiment station," he can 

 solve these problems from year to )ear without 

 much loss of time and land, and with great 

 profit. 



The food elements most apt to be lacking in 

 ordinary soils are nitrogen, phosphorus, and 

 potassium. The appearance of the plants (see 

 page 80) often indicates their specific needs. 

 But one may find out more definitely by apply- 

 ing one kind of fertilizer — as, sulphate of potash 

 — to one plot of a field, and another kind of fer- 

 tilizer — as, sodium nitrate or superphosphate of 

 lime — to another plot, and a complete fertilizer, 

 or mixture of the three (see page 94), upon a 

 third plot, and comparing results carefully with 

 those of a plot to which no fertilizer has been 

 added. The next year the whole field may be 

 treated with the particular fertilizer which the 

 results of these experiments show is needed. If 

 other conditions are right a heavy yield may be ex- 

 pected. These experiments may show the need of 

 one or of all three of the fertilizers — nitrate, phos- 

 phate, or potash ; or it may be that none of them 

 increase the yield, when one must look to other 

 conditions of soil, or plant, to solve the difficulty. 



III. Fertilization of the Soil. 



I . Commercial Fertilizers. 

 (i) Nitrogenous Compounds. — The nitro- 

 genous compounds used as commercial fertilizers 



