270 



SCIENCE 



[N. S. Vol. XXVI. No. 661 



their share of work towards a complete and 

 correct soil diagnosis. We can not stay 

 now to consider how far our methods to- 

 day are satisfactory towards that end ; we 

 all admit they are far from perfect. 

 Nevertheless, there has been a marked ad- 

 vance during the past ten years, and there 

 are at the present time earnest and skilful 

 workers engaged in this research whose 

 labors are yearly adding to our store of 

 knowledge on this important but exceed- 

 ingly difficult and complicated subject. 



Our own work in this matter has been 

 more particularly in tracing the relation 

 of organic matter and its concomitant, 

 nitrogen, to crop-producing power. 



1. Very early in our soil studies I was 

 impressed by the fact that our virgin soils 

 of great productiveness were invariably 

 characterized by large percentages of or- 

 ganic matter and nitrogen, and that, on the 

 other hand, worn soils resulting from con- 

 tinuous grain growing or other irrational 

 systems, and soils from naturally poor 

 areas, showed meagre amounts of these 

 constituents. If we except soils from the 

 semi-arid districts of the west, and the 

 muck soils of the east, these statements 

 will apply, more or less strictly, to all 

 types of soils, from heavy clays to light 

 sandy loams. 



2. We found, further, that in those soils 

 from humid districts there was a relation- 

 ship between the organic matter and the 

 nitrogen — that what affected or destroyed 

 the former dissipated the latter; while, on 

 the other hand, the methods that led to 

 an increase of the organic matter also 

 raised the nitrogen content. Undoubtedly 

 these two constituents stand and fall to- 

 gether. 



3. Another feature of importance was 

 that accompanying a fair organic content 

 there was usually a goodly proportion of 

 available phosphoric acid, potash and lime : 



that is, according to the Dyer method of 

 determination. 



4. Lastly, it was evident that the propor- 

 tion of organic matter present influenced 

 in a marked degree the capacity of the soil 

 for holding moisture, and in several other 

 important particulars affected the me- 

 chanical condition. 



We have not been able to study the effect 

 of the organic matter and nitrogen content 

 on bacterial life, but I believe it will be 

 shown that, other conditions being equal, 

 there is a distinct relationship between 

 these important factors, the latter being 

 determined by the former. Further, that 

 fertility will be found largely dependent 

 upon the rate of nitrification during the 

 growing season, which, though largely 

 regulated by temperature and moisture, 

 must be materially affected by the amount 

 of the food supply that the microorganisms 

 find in the form of partially decomposed 

 nitrogenous organic matter. 



Another matter closely connected with 

 nitrification is the liberation in available 

 forms of mineral plant food. Is it not 

 more than probable that the two processes 

 are coexistent and interdependent — pos- 

 sibly identical? 



As the years went by and our data in- 

 creased it became ever more and more plain 

 that in the semi-decomposed organic mat- 

 ter and its nitrogen we had factors of 

 primary importance and of the greatest 

 diagnostic value— that from them we could 

 obtain a fairly clear insight into the char- 

 acter of the soil— chemical, physical and 

 biological. 



Since, then, we have reason to believe that 

 the percentage of nitrogen is directly and 

 indirectly a measure of the soil's fertility, 

 and that this percentage is largely influ- 

 enced by the treatment the soil receives, 

 we may consider the data from one or two 

 series of experiments to show the rate of 



