CHAPTER III 



FERTILIZERS 



Need of Fertilizers. — If a soil is cropped year after year 

 and no plant food is added, the supply in the soil will be- 

 come exhausted, or there will be such a small amount left 

 that the crops cannot get enough food to grow well and' 

 will produce very little or fail entirely. There is a number 

 of different materials that may be applied to the soil to 

 supply the plant food needed. Such materials are called 

 fertilizers. Barnyard manure is the most common fer- 

 tilizer used. Materials that are purchased for fertilizer, 



Figure 12.— Pastunng, Live stock can be kept ordinarily more cneaply on past 

 ures than in any other way. Pasturing also improves the soil. 



such as Ume, ground phosphate rock, sodium nitrate, waste 

 from slaughter houses, etc., are called commercial ferti- 

 hzers, because they are bought and sold. 



Plant Food.— Plants, like animals, have to be fed, and, 

 like animals, they need more than one kind of food. Therp 

 is a number of different elements which are needed for the 

 complete growth of plants. The soil, air, and water in the 

 soil furnish most of the elements needed in such great 

 abundance that there is no danger of the supply's ever 

 becoming exhausted. There are only four elements that 

 are likely to be lacking even in soils that have been cropped 



