THE FOOD OF PLANTS 27 



quantities in most soils, but plants need very little of 

 these, and practically always have sufficient. Plants need 

 much calcium, but most soils contain much of it. Sugar- 

 cane is the only important Philippine crop likely to need 

 more calcium than is present in the soil. 



FERTILIZERS 



Calcium. Substances containing plant food, which are 

 added to the ground to make it more productive, are 



onuis from one acre of fertilized and one acre of 

 Loxton and Palmlands Ivstate, Ccvlon 



called fertilizers. Ground which has been producing 

 sugar for many years is often very weak in calcium. If 

 limestone or coral, which contain much calcium, be 

 crushed and put on the ground, there will be a greater 

 yield of sugar; the limestone or coral is a fertilizer. 



