SOIL DEFICIENCIES 



247 



easily controlled than field conditions, and certain problems can 

 be much more easily studied. Conditions are relatively more 

 favorable than in the field, and the relation between the pot ex- 

 periments and field results, must be traced out. 



The pots used vary much in size, shape, and material. 

 They may be made of glass, galvanized iron, enameled 

 iron, or earthenware, and may vary in size from a few 

 inches in diameter to those which cannot well be handled 







Fig. 58. Pot experiments. New Jersey Station. 



and are imbedded in the ground. Galvanized iron is open 

 to the objection that the zinc may corrode and form 

 poisonous compounds. An ordinary form of pot consists of a 

 cylindrical vessel about 8 inches in diameter and 8 inches deep. 

 It first receives a layer of gravel, covering a metal or glass 

 ventilating tube which reaches above the top of the pot. The soil 

 is placed on this, and receives the desired additions. The seed 



