852 



HOETICULTURE 



December 14, 1912 



SOILS. 



(Read by Alfred Burton, before the 

 Florists' Club of PbiladelpUia.) 



What Is soil? Soil is the home of 

 the roots of the plant. Soil is the store- 

 house for that part of the food which 

 the plant takes in through its roots. 

 Soil is the laboratory or kitchen where 

 the food is prepared. And this work 

 goes on unceasingly. Lastly soil is a 

 support to hold the plant firmly in its 

 place. 



But what is soil? Soil is finely di- 

 vided rock as can be readily seen with 

 a microscope, clay being the finest 

 and sand and gravel the coarsest of 

 the divisions. In between the sand 

 and the clay, we have what are gener- 

 ally known as loamy sand, sandy 

 loam, loam, clayey loam, loamy clay 

 and clay. 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 unnum- 

 bered variations of soils. 



Now if we consider soils as broken 

 and decomposed rock, the first ques- 

 tion that comes to our mind is, how 

 and when were the rocks which origi- 

 nally covered the face of the earth 

 converted into soil. Certainly ages and 

 ages before man appeared on the earth. 

 In fact before animal life of any kind 

 could exist there must have been vege- 

 tation; and vegetation of the higher 

 forms could not exist on bare rocks. 

 Probably the commencement of the 

 disintegration was coincident with the 

 appearance of plant life in the lowest 

 form. 



Geologists tell us that the earth was 

 once a molten mass, also that the 

 water which now composes the oceans, 

 was probably in the form of a dense 

 vapor which surrounded the red hot 

 earth. Naturally, the earth began to 

 cool, and as it cooled, it contracted. 

 The result of this was that the surface 

 subsided in some places and wrinkled 

 in others, thus producing the sea 

 basins, valleys and hills. When the 

 surface had cooled sufficiently, (and 

 this cooling was hastened by the vapor 

 in the air) the vapor condensed and 

 fell as rain or snow, and thus began to 

 wear or weather the rock. Frost and 

 heat assisted the water In disintegrat- 

 ing and breaking up the surface. Some- 

 time after the surface had cooled suf- 

 ficiently vegetation began its existence. 

 First in almost microscopic forms, the 

 mosses and lichens which are able to 

 extract nourishment from almost any 

 rock. These by their death and decay 

 formed a very thin film of vegetable 

 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 vegeta- 

 tion, and so on till grass, shrubs and 

 even trees were able to exist. This de- 

 cayed vegetable matter in the soil is 

 called humus. And this humus helps 

 to disintegrate the rock by holding 

 moisture and by supplying acids which 

 increase the solvent powers of the 

 water on the rock. When a soil con- 

 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 matter 

 that has only partly decomposed under 

 water is called peaty soil. Such soils 

 are found in swamps and bogs and are 

 generally 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 debatable 

 question whether plants derive any 

 nourishment from it direct, it is of 

 great importance in enabling the soil 

 to hold water, in making the soil more 

 triable and easily worked, and in sup- 

 plying carbonic acid which feeds the 

 plant, and acts on the soil dissolving 

 and making available other foods such 

 as soda, potash and magnesium which 

 are held in an insoluble state in the 

 soil. Humus also gives the dark color 

 to the soil which enables it to ab- 

 sorb the best rays of the sun more 

 readily and thus warm up more quickly 

 in the spring. 



True clay is composed of silicate of 

 alumina but the term clay in agricul- 

 ture is employed rather loosely, being 

 given to soils that contain a large per- 

 centage of impalpable rock dust with 

 very little of the true clay present. 

 Some authorities give the following 

 percentage composition of the various 

 soils: 



Clay or 

 Impalpable 

 matter. Sand. 



Per cent. Per cent. 



Heavy clay contains 75 to 90 10 to 25 



C'ay loam " 60 to 75 25 to 40 



Loam " 40 to 60 40 to 60 



Sandy loam " 25 to 40 60 to 75 



Light sandy loam 10 to 25 75 to 90 



Sand contains to 10 90 to 100 



These percentages are by weight of 

 the dry soil. We hear the 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 condition. A light 

 soil is one that contains considerable 

 sand, falls apart and works easily. A 

 heavy soil is one that is stiff and 

 tenacious, with more clay than sand. 

 It is a fact that a heavy soil actually 

 weighs less than a light one. 



A tenacious or adhesive clay soil can 

 be greatly improved by the addition of 

 sand, lime or vegetable matter, which 

 tend to separate the particles of clay. 

 It is this adhesiveness of clay which 

 causes heavy soils to crack when dry- 

 ing. Clay expands very much more 

 than light soils when wet and shrinks 

 upon drying and owing to the adhe- 

 siveness of the particles of which it is 

 composed, the shrinking causes the 

 cracks to appear. These cracks are 

 naturally injurious to the roots of the 

 plants, breaking and pulling them 

 apart. Sand does not change its bulk 

 by wetting or drying. Likewise a sandy 

 soil can be improved mechanically by 

 the addition of clay, lime or vegeta- 

 ble matter. Lime has the peculiar 

 power of lightening heavy soils and 

 also of making light soils hold to- 

 gether better. Bringing the two ex- 

 tremes to a happy mean as it were. 



The general chemical composition of 

 soils is extremely similar, owing to 

 the general mixing of the soil ingre- 

 dients that has been going on since 

 soil first began to form. Through the 

 action of water dissolving and carry- 

 ing material from place to place, 

 through the action of streams, floods 

 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 in- 

 gredient both by volume and weight 

 of all soils. It is a combination of sili- 

 con and oxygen. Aluminum probably 

 comes next in abundance, being a fun- 

 damental constituent of true clay, feld- 



spar and ice mica. Some of the other 

 elements in the soil are oxygen, which 

 occurs free and in combination with 

 nearly all the other elements. Carbon 

 occurs as part of the humus, also 

 united with calcium and magnesium in 

 the form of carbonates; also as car- 

 bonic acid gas which plays such an 

 important part in the solution of plant 

 food. Sulphur occurs as sulphates. 

 Hydrogen is united with oxygen in the 

 water. Chlorine occurs in limited 

 quantities generally in the form of 

 common salt sodium chloride. It seems 

 to be in some way essential to plant 

 life. Phosphorus is never found in 

 nature in a tree state but always com- 

 bined with some other substance. It 

 is very generally distributed through 

 the soil but in small quantities and is 

 very essential to plant life. Nitrogen 

 is found in the soil in a combined form 

 in the humus and the vegetable and 

 animal matter, which upon decaying 

 give up the nitrogen in the form of 

 ammonia, which is turned into nitric 

 acid by bacteria. The nitric acid 

 unites with potash, soda or other soil 

 ingredients and is taken up by the 

 plant as a nitrate. Nitrates are ex- 

 tremely soluble and easily washed out 

 of the soil. Calcium and magnesium, 

 in the form of carbonates compose the 

 limestone beds of the earth. Both cal- 

 cium carbonate or lime, and magnesia 

 are necessary plant foods, and both are 

 generally present in the soil in suffi- 

 cient quantities to supply the plant 

 with the required amount. Potassium 

 is another element found in soils which 

 is very necessary. It is widely dis- 

 tributed as a constituent of some feld- 

 spars and micas. Sodium, which is the 

 base of common salt is also widely dis- 

 tributed, it very much resembles potas- 

 sium as a chemical element, but can 

 in no sense take its place in plant life. 

 Iron is always present in the soil in 

 sufficient quantities for the plant. 



It would be supposed, that to find, 

 what foods were necessary for soils,, 

 all that would be necessary would be 

 a chemical analysis of the particular 

 soil. Then if any element was found 

 to be lacking in sufficient quantity, the 

 addition of this or these elements, 

 would give the desired results. But 

 chemical analysis of the soil as they 

 have been made, unfortunately can and 

 do throw but a very dim and uncertain 

 light upon either the condition of the- 

 amount of plant food a soil may con- 

 tain. 



It is true that the results of these 

 analyses show a marked difference in 

 soils, but from the data at hand, these 

 variations may reasonably be supposed 

 to be due more to the relative size of 

 the soil grains than to any chemical 

 differences in the composition of the 

 soil. Taking an average of different 

 analyses of soils, the following has 

 been stated by one writer. On a farm 

 where a three year rotation composed 

 of corn, clover and oats was followed. 

 The corn and oats being sold, and the 

 straw, fodder and clover returned to- 

 the ground, the soil would contain pot- 

 ash enough to last 1521 years, soda 

 4050 years, magnesia 3300 years, lime 

 4367 years; phosphoric acid, only 542^ 

 years, sulphuric acid 292 years, and 

 soluble silica 17,650 years. 



These amounts of plant food are 

 what chemical analyses have told us 

 were in the top foot of soil, and we 

 know that plants send their roots for- 



