MANUAL FOR SUGAR GROWERS. 17 



this, though often rich in plant-food, requires skilled 

 management to keep it in good condition and ena- 

 ble it to produce large crops. 



Sand is the term applied to those soils possessing 

 but little coherence and very permeable by water ; the 

 mineral of which it is composed is frequently silica 

 or various silicious minerals. When the fragments 

 or individual particles are large, the term gravel is 

 employed. Pure sand, like pure clay and pure chalk, 

 is incapable of supporting vegetable life, so that nei- 

 ther of these substances in a pure state will consti- 

 tute what is generally understood by the term soil. 



A fertile soil consists of an admixture in varying 

 proportions of the three substances above named, 

 together with a suitable amount of vegetable matter 

 in a state of partial decay, and known as humus, 

 aiding the supply of nitrogen, and also such min- 

 eral matters as will supply the requisite potash, 

 phosphoric acid, lime, magnesia, iron, sulphuric 

 acid, and those mineral substances already referred 

 to ; for a soil to be fertile these must be in appro- 

 priate quantity, and in such condition that the grow- 

 ing plant constituting the crop can readily absorb 

 them, and the varying fertility of soils depends, 

 amongst other things, on the amount of available 

 plant-food present. These mineral matters are 

 usually present in the rocks from which the soils 

 are derived: thus volcanic rocks contain felspar, 

 whether whole or decomposed into clay ; and the soil 

 thus formed is generally rich in potash. Marls, or 

 chalky soils, frequently contain much phosphoric 

 acid, owing to the presence of that substance in the 

 2 



