TO DETERMINE THE PORE SPACE IN SOILS 19 



pied by the soil particles, the remainder being occupied by 

 water when the soil is very wet or by air when it is per- 

 fectly dry. For the best growth of crops the space not 

 occupied by the soil particles should be divided about 

 equally between water and air. If the space becomes 

 entirely filled with water, crops will not thrive, since their 

 roots will not be able to get the air necessary for their 

 growth. Sandy soil has larger spaces between the indi- 

 vidual soil particles, but the total amount of pore space is 

 less in the sandy soil than in the clay soil. 



