CHAPTER V 

 The Soils of the Cane-growing Regions 



The whole subject of the soil and of soils is one of such great magnitude 

 that no attempt is made here to treat the matter in any but the very barest 

 outline. Soil problems in their general significance are best studied in 

 specialized treatises of which many excellent examples are to be found ; 

 the principles there elaborated, though usually exemplified with reference 

 to the conditions and crops of temperate climates, are equally applicable 

 to the cane and tropical conditions. 



The cane itself is a plant that requires a large quantity of water, and 

 therefore a soil type that has a considerable water-retaining capacity is 

 preferable. Clay soils in general belong to this type, sandy soils l3ang at 

 the other extreme. The matter is, however, also influenced by the natiure of 

 the underlying stratum, by the height of the water table, and climatologically 

 by the rainfall and its distribution. Artificial factors come into play when 

 irrigation water is available in abundance, whereby the factor of water- 

 holding capacity is largely eliminated. 



Classification of Soils.— The classification of soils has been based by 

 students of the question on a variety of lines embracing the rock origin, 

 mode of formation, and physical structure. Based on rock origin, soils are 

 divided into two great classes : those derived from acidic, and those from 

 basic rocks. The former class includes those rocks that contain from 

 65 to 75 per cent, of silica, those with 40 to 55 per cent, being classed as basic 

 rocks. There is, however, no sharp line of cleavage, and one class passes' 

 insensibly into the other. MerriP gives the following examples of the 

 composition of typical rocks of the three types : — 



Acidic 



Intermediate 



Granite . . 

 Leparite . . 

 Obsidian 



f Syenite . . 

 I Trachyte 

 "1 Hyalotrachyte 

 I Andesite . . 



Silica per cent. 

 77*65 — 62-90 

 76*06 — 67* 71 

 82 -So— 71' 19 



72-20— 54-65 

 64 • 00 — 60 • 00 

 64-00 — 60-00 

 66-75—54-73 



Basic 



r Diabase .. 54* 00 — 48-00 



J Basalt .. .. 50-59 — 40-74 



1 Peridetite .. 42-65 — 33-73 



VPeridetite (Iron rich) 23-00 



The term andesite, which was used originally with regard to peculiar 

 formations in the Andes, seems to be used by some writers as almost synony- 

 mous with acidic. Generally the acidic formations are much older than are 



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