FORTY-SECOND ANNUAL REPORT. 



133 



total amount of plant-food contained in one acre, to any given depth. 

 Likewise, knowing the amount of plant-food removed by the crops grown, 

 also revealed by chemical analysis, the multiplication table will tell us 

 how many years our soil should be able to support a crop and also what 

 amounts of plant-food should be returned to the soil each year that the 

 fertility may be indefinitely maintained. Could anything be more sim- 

 ple? As you will readily perceive this view of the soil makes the amount 

 of the mineral plant food element (nitrogen, phosphoric acid and 

 potash) the index of fertility and they have very naturally been con- 

 sidered by many as the very foundation stones upon which successful 

 agricultural practice rests. No doubt every one of you have heard 

 these three plant-food elements, many times, extolled as the tripod of 

 agriculture. Consequently the scheme of practically all investigations, 

 until comparatively recently, has been with a view to ascertaining the 

 amounts of these elements in the soil and the amounts removed by 

 crops. 



With this view of soils it becomes quite imperative that we have 

 some standard by which a soil may be judged as good, bad or indiffer- 

 ent. Many persons have attempted to establish such a standard, but 

 strange to say, the various standards fail to agree. The one most gener- 

 ally referred to is that proposed by a German chemist. 



The only serious objection to such a standard is that the facts, as 

 revealed by actual experience do not, in a great many cases, conform 

 with these figures. It is also very evident that the man who proposed 

 this standard failed to recognize the fact that some crops are especially 

 adapted to certain kinds of soil, and that they will do far better upon 

 the particular kind of soil fitted to their needs, by nature, regardless 

 of its plant-food content, than upon any other kind of soil. 



According to this classification the great majority of the agricultural 

 soils of Michigan would be classified as good or rich, although we know 

 from actual experience that many of them are not up to, what we may 

 call, their normal productive capacity. 



The following table gives the analyses of a few soil samples that have 

 been made in our laboratory during the past few weeks. 



