178 



FOOD FOR PLANTS 



second than for the first 10-year period. With the 

 Nitrate of Soda, however, the figures are reversed 

 that is, the average yield for the second 10 years is 

 somewhat above that for the first 10 years. 



The question may well be raised as to why the 

 average yields on 4B, 17B and 18B should be less for 

 the second 10-year period than for the first, while 

 the yield on 8B has been well maintained for the 20 

 years. Since phosphoric acid and potash have been 

 supplied each year in liberal amounts, and lime has 

 been used at stated intervals, it would seem clear 

 that the falling off in yield must be due to a deficiency 

 of available nitrogen, notwithstanding the fact that 

 cylinders 17B and 18B receive each year just as much 

 nitrogen as SB, while 4B receives more than two and 

 one-half times as much as SB. 



TABLE 1 

 Yield of Dry Matter with Different Nitrogenous Materials. 



* Phosphoric acid, potash and lime, no nitrogen. 

 t First ten years. 

 t Second ten years. 



