SOIL IMPROVEMENT 115 



EXPERIMENT 



Fertilize a row in your garden with stable manure that has been pro- 

 tected against loss by leaching, washing, and heating. Fertilize another 

 row with the same amount of the same kind of manure that has been ex- 

 posed to the weather. Plant both rows in corn and cultivate in the same 

 way. What difference do you observe ? 



COMMERCIAL FERTILIZERS 



Crop Removal of Plant Food. Perhaps you have heard a farmer 

 say, "That crop has taken a great deal out of the land." That is 

 literally true. In the case of abundant elements, such as iron, 

 it is a matter of no importance; there is always enough left. But 

 you know there are some elements which are scarce in available 

 forms. The ^L^sphoric acid, nitrogen, and potash removed by 

 m>ps must be replaced if the soil is to continue productive. 



Supplying Elements Needed. Much plant food can be supplied 

 and made available by deep and thorough cultivation, by proper 

 rotation of crops, and by raising legumes. For crops which make 

 large demands on soil fertility and in order to give proper balance 

 of plant food, a farmer sometimes finds it desirable to supply some 

 elements in concentrated, readily available forms. For these pur- 

 poses, he uses commercial fertilizers. By their wise use, farmers 

 gain thousands of dollars; by their unwise use, they lose more. 



Commercial Fertilizers. What are the sources of thesq com- 

 mercial fertilizers ? Some are obtained from vast natural deposits 

 in Germany, South America, the United States, and other countries. 

 Others are the by-products of certain manufactures, such as gas 

 from coal, and oil from cotton seed. 



They contain plant food in a more concentrated and more 

 directly available form than it exists in green and stable manures. 



