FERTILIZERS 173 



space may be only an inch for young plants, but is allowed 

 to increase as the young plants grow. The book "Soilless 

 Gardening" must be consulted for the formula and the many 

 details of the system. 



Dr. J. W. Shive, at the New Jersey Agricultural Experi- 

 ment Station, devised various ways of bubbling air into the 

 solution without the use of the seedbed. The bubbles are 

 best if they are very small. Ordinary fish aquaria aerators 

 seem to be satisfactory. 



A third method, which is very simple to operate, employs 

 sand as a medium for the roots, and the nutrient solution is 

 dripped on the top and allowed to drain away at the bottom. 

 This insures good aeration if the sand is of the proper coarse- 

 ness to allow the water to drain through freely. 



Simultaneously workers at the Agricultural Experiment 

 Stations of Purdue University and New Jersey devised a 

 fourth method, used commercially quite frequently, employ- 

 ing a fine gravel or cinders in place of the sand. The gravel 

 is too coarse for water to move rapidly by capillarity, there- 

 fore the gravel is flooded two or more times each day to keep 

 it wet and allowed to drain back to a storage tank. The solu- 

 tion is kept in a tank beneath the gravel plant beds, and 

 electric pumps, controlled by time clock switches, work auto- 

 matically. This method gives the maximum of aeration and 

 for large installations a minimum of labor. The solutions 

 are tested two or three times each week and supplied with 

 needed elements. 



The writer made use of methods one, three, and four in 

 the greenhouse with very simple, inexpensive equipment, as 

 shown in the photograph (Plate XIV). Tomatoes, buck- 

 wheat, and corn all grew to maturity, the latter with a height 

 of more than ten feet. Two problems — the nitrogen was too 

 abundant and the pH too high — offered some difficulty, but 

 both were later regulated satisfactorily. The pH must be 

 kept below 6.5 if the solution is warm, to keep the iron in 



