October. 1913. 



THE GARDEN AND FIELD. 



214 



What is Soil. ? 



Soil is the home of the roots of 

 the jilant. Soil is the store-house 

 for that part of the food which the 

 plant takes in throujf'hv its roots. 

 Soil is the laboratory or kitchen 

 where the food is prepared. And 

 this work <^oes on iinceasinglv. 

 Lastly, soil is a support to hold 

 the plant firmly in its place. 



But what is soil ? Soil is finely 

 divided rock as can "be readily seen 

 with a microscope, clay being the 

 finest and sand and gravel the 

 coarsest of the divisions. In be- 

 tween the sand and the cla}", we 

 have what are generally known 

 as loamy sand, sandy loam, loam, 

 clavey loam, loamy clav and clav. 

 These divisions are based upon the 

 size of the soil grains and the 

 different percentages of each size 

 in a given soil. , They are, of 

 course, not arbitrarily fixed, there 

 being unnumbered variatijns of 

 soils. 



N'ow if we consider soils as bro- 

 ken and decomposed rock, the 

 first question that comes to our 

 mind is, how and when were the 

 rocks which originally covered the 

 face of the ' earth converted into 

 soil. Certainly ages and ages be- 

 fore man appeared on the earth. 

 In fact liefore animal life of any 

 kind could exist there must have 

 been vegetation ; and vegetation of 

 the higher forms could not exist 

 on - bare rocks. Prol)ably the 

 commencement of the disintegra- 

 tion was coincident with the ap- 

 pearance of plant life in the lowest 

 form. 



— In the Beginning. — 



(icologists tell us that the earth 

 was once a molten mass, also that 

 the water which now coimposes the 

 oceans, was i)roljably in the form 

 of a dense vapor which surrounded 

 the red hot earth. Naturally, the 

 earth began to cool, and it is cool- 

 ed, it contracted. The result of 

 this was that the surface subsided 

 in some places and wrinkled in 

 others, thus ])roducing the sea 

 basins, valleys and hills. When 

 the surface had coolf.'d sulliciently 

 (and this cooling was hastene<l liv 

 the vapoT in the air) the vapor 

 condensc-d and fell as rain' or snow, 

 and thus began to wear or 

 weather the rock. Frost and heat 

 assisted the water in disinteg- 

 rating and breaking up the surface. 

 Some time after the surface had 

 coole<l su/ncientlv vegetation began 

 its existence. First in almost mi- 



croscopic forms, the mosses and 

 lichens which are able to extract 

 nourishment from almost any rock. 

 These by their death and decay 

 form.ed a very thin film of veget- 

 able matter on the rock and a 

 stronger growth took place which 

 in turn died, decayed, and gave 

 way to ' a still stronger and higher 

 form of vegetation, and so on tdl 

 grass, shrubs, and even trees were 

 able to exist. This decayed veget- 

 able matter in the soil is called 

 humais. And this humus helps to 

 disintegrate the rock by holding 

 moisture and b)^ supplying acids 

 which increase the solvent powers 

 of the water on the rock. When 

 a soil ccn tains much of this 

 humus, it is called a vegetable 

 mold. Rich garden soils are good 

 'representatives of this class. A 

 soil that contains vegetable mat- 

 ter that has only partly decom- 

 posed under water is called peaty 

 soil. Such soils are found in 

 swamps and bogs and are gener- 

 ally sour and need to be aerated 

 and limed before using. 



While organic matter or humus 

 is by no means indispensable to 

 plant life, and though it is a de- 

 liatable ^iuestion whether plants de- 

 rive any nou-rishment from it di- 

 rectly, it is of great importance m 

 making the soil more friable and 

 easily worked, and in supplying 

 carbonic acid which feeds the plant,, 

 and acts on the soil dissolving 

 and making available other foods 

 such as soda, potash and mag- 

 nesium which are held in an in- 

 soluble state in the soil. Humus 

 also gives the dark color to the 

 soil which enables it to absorb the 

 best ra}'s of the sun more readily 

 and thxis warm up mo're quickly in 

 the spring. 



— Clay. — 



True clay is composed of silicate 

 of alumina but the term clay in 

 agriculture is employed rather 

 loosely, being given to soils that 

 contain a large percentage of im- 

 palpable rock dust with very little 

 of the true clay present. 



We hear rather misleading terms 

 light and heavy applied to , soils. 

 These terms have no reference to 

 the weight of the soil but are used 

 in reference to the mechanical con- 

 dition. A light .soil is one that 

 contains considerable sand, falls 

 ai)art and works easily. -A heavy 

 soil is one that is stiff and tenaci- 

 ous, with more clay than sand. It 

 is a fact that a heavy soil actual- 

 ly weighs less than a light one. 



A tenacious or adhesive clay soil 

 can be gneatly improved by the 

 addition of sand, lime or vegetable 

 matter, which tend to separate the 

 particles of clay. It is this ad- 

 hesiveness of clay which causes 

 heavy soils to crack when drying. 

 Clay expands very much more 

 than light soils when wet and 

 shrinks upon drymg and owing to 

 the adhesivfeness of the particles of 

 which it is composed, the shrink- 

 ing caus'es the cracks to appear. 

 These cracks are naturally injuri- 

 ous to the roots of the plants, 

 breaking and pulling them . apart. 

 Sand does not change its bulk by 

 wetting oi" drying. Likewise a 

 sandy soil can be improved me- 

 chanically by the addition of clay, 

 lime or vegetable matter. 'Lime 

 has the pecidiar power of lighten- 

 ing heavy soils and also of making 

 light soils hold together better. 

 Bringing the two extremes to a 

 happy mean as it were. 



— Chemical Composition. — 



The general chemical composition 

 of soils is extremely similar, ow- 

 ing to the general mixing 'of the 

 soil ingredients that has been go- 

 ing on since soil first began to 

 form. Through the action of 

 water dissolving and carrying ma- 

 terial from place to place, through 

 the action of streams, Hoods and 

 glaciers, of burrowing animals, 

 worms, etc., of the wind and even 

 plants. Silica or quartz, because 

 it is so hard and insoluble, is the 

 chief ingredient both by volume 

 and weight of all soils. Aluminium 

 prol)ablv comes next in abundance, 

 being a fundamental con.stituent of 



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