324 NATURE AND PROPERTIES OF SOILS 



fairly reliable guide in some cases to the fertility of the soil 

 under specific consideration. 



Although the relationship of organic matter and nitrogen 

 to soil fertility is so close that certain generalized tables x may 

 be cited for the interpretation of chemical data, no close cor- 

 relation is possible, especially where soils of markedly different 

 character are compared. So many other factors may enter 

 that practically no opinion can be formed regarding the prod- 

 uctivity of a soil unless other and more detailed data are 

 available. 



An interesting example of where the nitrogen content fails 

 to indicate the relative fertility of two soils is found in certain 

 unpublished data from the Cornell Agricultural Experiment 

 Station. Two soils are being studied in the lysimeter tanks — 

 Dunkirk silty clay loam and Volusia silt loam. In Table 

 LXXIII is given the nitrogen and calcium content of these 

 soils and the pounds of nitrogen removed to the acre by maize, 

 oats, and barley, respectively, for the years 1915, 1916, and 

 1917. The treatment and handling of the soils compared has 

 been the same. 



While the nitrogen, phosphoric acid and potash contents of 

 these soils are about the same, a marked difference is noted in 

 their productivity. This may be due, at least partially, to 

 the calcium content, which is rather high in the Dunkirk, 

 especially in the subsoil. In comparing soils over wide areas 



1 The following tentative classification of soils on the basis of their 

 percentages of organic matter and nitrogen is offered for generalized 

 field use: 



Description 



Percentage of 

 Organic Matter 



Percentage of 



Nitrogen 



Low 



Medium. . . 

 High .... 

 Very high 



.0- 3.0 



3.0- 6.0 



6.0-10.0 



above 10.0 



.00- .10 



.10- .25 



.25- .40 



above .40 



