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PRINCIPLES OF AGRICULTURAL CHEMISTRY 



being grown on one of the four fields every year. There are at 

 least four plots of the same treatment, one in each field. The 

 fertilizer is applied to the corn and wheat only. 



Son, TREATMENT (PENNSYLVANIA). 



N stands for 48 pounds nitrogen, 2N for 96 pounds, 3N for 144 

 pounds per acre. Blood was used in the first 24 plots, except No. 

 n, Nitrate of soda in plots 26-7-8 (marked Na) and sulphate of 

 ammonia in plots 30-1-2 (marked SO 8 ). K signifies 160 pounds 

 muriate of potash, P for phosphoric acid in dissolved bone black. 

 Manure was used at the rate of 12, 16, and 20 tons per acre. 

 Plaster is 640 pounds land plaster (gypsum). CaO is 2 tons 

 caustic lime. Limestone is 4 tons ground limestone. Blood and 

 bone were used on plots 1 1 and 35 for nitrogen and phosphoric 

 acid, respectively. 



Comparative Effects of Different Plant Foods. In comparing 

 the results of plot experiments, it is important to determine the 

 effect of the individual fertilizing constituents, namely, of phos- 

 phoric acid, nitrogen, potash, or lime. The fertilizing constituents 

 exert some influence upon the relative action of each other, but 

 nevertheless it is often advisable to estimate the value of each in- 

 dependently. This can be done by subtracting the yield without 

 the constituent in question from that with it. Thus the yield with 

 phosphoric acid, potash, and nitrogen less that with phosphoric 

 acid and potash gives the effect of nitrogen; by subtracting the 

 yield with phosphoric acid and nitrogen we get the effect of 



