CHAPTER XXI. 



SOILS OF ARID AND HUMID REGIONS (Continued]. 



SOILS OF THE TROPICS. 



WITHIN the ordinary limits of atmospheric temperatures, 

 and in the presence of adequate moisture, chemical processes 

 active in soil-formation are intensified by high and retarded by 

 low temperatures, all other conditions being equal. We can 

 usually artificially imitate, and produce in a short time by the 

 application of relatively high temperatures, most of the chemi- 

 cal changes that naturally occur in soil-formation. While it is 

 true that the changes of temperature are nearly as great in the 

 tropical as in the temperate climates, these changes all occur 

 at a higher level and within the limits favoring bacterial and 

 fungous action. 



This being true we should expect that the soils of tropical 

 regions should, broadly speaking, be more highly decomposed 

 than those of the temperate and frigid zones, and that the 

 intensified processes continue currently. This fact has not 

 been as fully verified as might be desirable, by the direct 

 comparative chemical examination of corresponding soils from 

 the several regions, owing to the want of uniformity in 

 methods and the fewness of such investigations in tropical 

 countries. Yet the incomparable luxuriance of the natural as 

 well as artificial vegetation in the tropics, and the long duration 

 of productiveness that favors so greatly the proverbial easy- 

 going ways and sloth fulness of the population of tropical 

 countries, offers at least presumptive evidence of the practical 

 correctness of this induction. 



In other words, the fallowing action, which in temperate 

 regions takes place with comparative slowness, necessitating 

 the early use of fertilizers on an extensive scale, is much more 

 rapid and effective in the hot climates of the equatorial rainy 

 belt; thus rendering currently available so large a proportion 



398 



