68 



CROPS AS FEEDERS 



must give up one hundred eighteen pounds of nitrogen, seven- 

 teen pounds of phosphorus, ninety-two pounds of potassium and 

 38.5 pounds of calcium. 



In case of a fifteen-ton cabbage crop, at least eleven tons of 

 material are left on the field. Thus a fifteen-ton cabbage crop 

 requires for its production approximately one hundred eighty 

 pounds of nitrogen, sixteen pounds of phosphorus, one hun- 

 dred twenty-five 

 pounds of potas- 

 sium and sixty- 

 two pounds of 

 calcium. 



In case of 

 hemp, it would 

 seem that a soil 

 needs to give 

 up only small 

 amounts of the 

 elements to pro- 

 duce a good crop, 

 and that it ought 

 to grow well on 

 poor soils. On the 

 contrary, it re- 

 quires a fertile soil 

 to grow a good 

 crop of hemp. 



Root Systems 

 of Crops Differ. — 



Fig 26 — Root-hairs are the absorbing portion of plant SomO plants have 



roots These root-hairs comemto mtimate contact with the soil ^vxr+A-nai-vrA anrJ \x^c^}^ 



A , root-hairs of mustard plants, with soil adhering and with soil tJA teilfei V t; tAllU wtill 



removed B, root-hairs of wheat, when very young, and four Hp-irAlnn^rl rnn-/- qa?-- 



weeks later (After Sachs ) ueveiopeu TOOT, sy 



stems enabling 

 them to draw plant-food elements and water, particularly, from 

 large volumes of soil (Figs. 26 and 27) . Corn and alfalfa are typical 

 examples. Such crops as onions, cabbage and beets have much 

 less extensive root systems. 



It is the nature of some plants to develop fibrous and much 

 branching roots largely in the tilled portion of the ground — ^these 

 are commonly called shallow rooted plants. 



Farm Plants are Interesting Subjects for Study. — In the 



AA 



