THE SOIL AND THE CROP 39 



of barnyard manure will improve the next crop, and is 

 the best remedy for yellow and sickly plants. 



Plants as Fertilizers. In the next place, clover, 

 alfalfa, peas and like plants which bear their seeds in 

 pods may grow well on this kind of soil, because they 

 have the power of using the nitrogen of the air in a 

 way that will be explained later. These plants store 

 up the nitrogen that they take from the air, and if they 

 are plowed under when full grown they add this store 

 of nitrogen to the soil, besides forming an excellent 

 soil mulch. While generally not so good as barnyard 

 manure, clover is an excellent means of restoring nitro- 

 gen to the soil. In some cases it does more for the 

 soil than barnyard manure can, and it is easier of 

 application. 



Commercial Fertilizers. Another method consists 

 of applying commercial fertilizers containing nitro- 

 gen directly to the soil. These may be bought in the 

 market, but as yet they are little used by western farm- 

 ers, because manure and clover are ordinarily cheaper, 

 more convenient and easier to apply. Guano, saltpeter, 

 fish and animal refuse from slaughter houses are the 

 principal commercial fertilizers that contain large 

 amounts of this much-needed plant food. 



Phosphoric Acid. A shortage of phosphoric acid in 

 the soil is usually shown by small, undeveloped and 

 shrunken seeds. The grain does not "fill well," as the 

 farmer says. The ground has been carefully prepared, 

 tilled and drained. What is he to do? Nothing is 

 simpler. Apply phosphoric acid fertilizers to the soil. 



