66 CHAPTER V 



Tropical Soils. — It may not be going too far to say that the tropical soils 

 'upon which the sugar cane is grown fall into two great divisions — those 

 'derived from acidic rocks of very ancient formation, and those derived from 

 >basic rocks due to comparatively recent volcanic agency. The former 

 class includes most of the continental areas where the cane is grown, and 

 here belong the regions derived from the Andes, Peru, and the north-eastern 

 part of South America which has been built up by the Amazon, the alluvial 

 plains formed by the Nile, and by the Mississippi and the Red River, and the 

 central or Mackay district of Queensland. In much of Java, too, andesite 

 formation is dominant, although recent basaltic rocks also occur. In the 

 other formations fall most of the insular areas formed by comparatively 

 recent volcanic action, and here are included the chain of the West Indian 

 Islands, the islands of Mauiitius and Reunion, the Phihppines and the 

 Hawaiian Archipelago. The Bundaberg district of Queensland is of this 

 formation also. This distinction, which is broad rather than particular, is 

 open to modification in many ways, the most important being the frequent 

 occurrence of limestone rocks, whether of coralline or other formation. 

 Tertiary limestone formations are characteristic of Cuba, and they also modify 

 the soil type in Java and in the Philippines ; the island of Barbados is an 

 instance of an essentially unmodified limestone formation. 



A peculiar type of soil especially connected with the tropics is that 

 known as a laterite. This term derived from latus, a brick, was originally 

 used in connection with certain brick-red formations, forming a super- 

 ficial covering over a great part of India. These soils are essentially derived 

 from basaltic rocks, and are characterized by a very high percentage of iron 

 and alumina. When wet they resemble a typical clay, but differ therefrom 

 in not adhering after drying ; they are extremely hygroscopic, and when air- 

 dry contain as much as 20 per cent, of water. Besides occurring in India, 

 the red soils of Cuba and other parts of the West Indies, and a great 

 portion of those of the Hawaiian Islands, are typical laterites ; they also 

 occur to a considerable extent in the sugar-producing areas of Brazil. 



Yet another distinction may be made between soils as they occur in 

 the tropics, based on the climatic conditions obtaining over the epoch 

 of their formation. They fall into the arid and humid types ; the former 

 are often red in colour, and the latter are generally black. The colour in 

 the latter case is due to the large proportion of organic matter present, and 

 this forms the main distinction between the two types, since climatic condi- 

 tions do not affect the composition of the soil, as derived from its rock 

 origin. This distinction into red and black soils is very common ; it appears 

 in the Hawaiian Islands, the upland soils formed in a zone of heavy rain being 

 black, while the arid littoral formation affords a typical red laterite. The 

 Cuban soils are also classed as red and black soils, the same distinction 

 obtaining in Barbados. This difference is also recorded in Grainger's 

 didactic poem " The Sugar Cane," written in 1768. 



Analysis of Soils. — Many years ago the composition of the soil, as obtained 

 by analysis, was thought to be the dominant factor in determining its fer- 

 tility. With added experience it has come to be recognised that other 

 factors such as physical condition, tilth, drainage, bacterial activity, and 

 the presence of relatively small quantities of obnoxious substances, have 

 at least an equal importance. The productivity of a soil is, however, not so 

 xnuch governed by the combined effect of all the controlling factors as by 



