AGRICULTURE 



tity. If present, they are often in forms which the plant cannot 

 use. 



A chemist will analyze a piece of granite and tell you that it 

 contains all the elements needed for plant food. But they are 

 locked up in forms which the plant cannot use ; they are ' un- 

 available,' we say. The plant can no more feed on them than 

 we can clothe ourselves in the cotton fiber in the boll, or than 



we can make bread of unhusked 

 corn. 



Soil Texture. Even in soil well 

 supplied with plant food, crops may 

 not thrive. The soil texture may be 

 unfavorable. You have learned 

 something about the differences in 

 soils and how texture affects rela- 

 tions to water, air, and heat. You 

 have learned also, that these three 

 things have an important influence 

 on the growth of plants. You un- 

 derstand, then, that while sand, 

 clay, and humus furnish little plant 

 fo^ they affect plant growth and 

 crop yield. 



Each kind of soil has vegetation especially adapted to it. 

 A sandy soil, if well supplied with plant food, is adapted to 

 tubers and root crops; it yields up plant food fully and freely, 

 and the growing roots easily push its particles aside. Clay soils 

 are adapted to grain and grass crops and to other plants with fine, 

 fibrous roots that can make their way among the tiny particles 

 to collect plant food and water. Certain plants, such as blue grass, 

 thrive best in a limestone soil. The limestone region of Kentucky 



The beet on the left was grown in 

 mellow, well-tilled soil; that on the 

 right was grown in rough, hard clay. - 



