PENNSYLVANIA FIELD EXPERIMENTS 



431 



TABLE 81. PENNSYLVANIA EXPERIMENTS : FOUR- YEAR ROTATION 

 Summary of Financial Results from Soil Treatment in Four-year Rotation 



with yields of the unfertilized land during the previous 12 years. 

 By this means only are we able to avoid the exaggerated influ- 

 ence which is always credited to the soil treatment when com- 

 parison is made with the decreasing productiveness of unfertilized 

 check plots. 



