SOII, ANALYSIS AND INVESTIGATION 15 



practice, and a rotation should be followed and repeated several 

 times before conclusions regarding the productivity of the soil 

 are justified. If, however, the rotation has been well managed, 

 the cultivation, fertilizing and soil management generally been 

 well done for sixteen, twenty or more years, the soil has material- 

 ly changed, and there can be no assurance that the treatment 

 than best for it, is that which was best at the beginning of the 

 experiment. Therefore the method throws no certain light on 

 the productive power of the soil, or the availability of its 

 mineral plant-food constituents. Although much has been 

 learned from plot experiments, and especially from the better 

 controlled pot experiments, they are inadequate to meet the 

 fundamental problem of the relation of the chemical character- 

 istics of the soil to its crop-producing powers. 



