ARABLE LAND. 



ARABLE LAND. 



162 



according to their size ; and the finest siliceous sand, when examined 

 with a magnifying glass, has the appearance of irregular fragments of 

 stone without any cohesion between them. 



Siliceous sand holds water in its interstices by simple cohesive 

 attraction in proportion to its fineness. It heats and cools rapidly, 

 letting the water pass through it readily, either by filtration or evapo- 

 ration. Its use in the soil is to keep it open, to let the air and water, 

 as well as those other substances on which the growth of plants 

 depends, circulate through it. Unmixed, it dries so rapidly that no 

 vegetation can continue in it, unless a constant supply of moisture 

 be given by irrigation. A small portion of clay will much improve 

 light sands ; it takes a large quantity of sand to correct the tenacity of 

 clay. 



Lime in its pure state is familiar to every one as the basis of the 

 mortar used in building. It is produced by burning marble, chalk, 

 limestone, or shells, in a great heat. In the stones which are formed 

 principally of lime, it is combined generally with carbonic acid, which 

 separates from it by the operation of burning, in the form of an air or 

 gas, hence called fixed air, from its being thus fixed in a stone. These 

 stones, of various degrees of hardness, are now all classed under the 

 name of carbonates of lime. 



Lime unites readily with water, which it also absorbs from the 

 atmosphere. It then becomes dalcetl. By uniting with carbonic acid, 

 it returns to its former state of carbonate ; with this difference, that, 

 unless much water be present, it remains a fine impalpable powder. 

 Pure lime is soluble in water, though sparingly; a pint of water 

 cannot dissolve more than about twenty grains : the carbonate is not 

 soluble in simple water ; though in water containing carbonic acid, it 

 readily dissolves. Carbonate of lime has a powerful effect on the 

 fertility of a soil, and no soil is very productive without it. It is 

 consequently used extensively as an improver of the soil, otherwise 

 called a manure ; but its use in this respect, and the mode in which it 

 acts, will be given in the articles MANURE and LIME. 



Carbonate of lime, as an earth, is neither so tenacious as clay, nor 

 so loose as sand. In proportion to the fineness of its particles it 

 approaches to the one or the other, and when the parts are large and 

 hard it takes the name of limestone gravel. Its distinguishing feature 

 is its solubility in acids, which it neutralises, depriving them of their 

 noxious qualities in the soil. 



A proper mixture of these three earths, in a due state of mechanical 

 division, forms a soil well fitted to the growth of every species of 

 plants, especially those which are cultivated for food ; and nothing 

 more is required than a proper climate as to heat, a proper degree of 

 moisture, and sufficient nourishment, to make all the plants generally 

 ted thrive most luxuriantly in such a mixture, which is usually 

 called a loam. 



But there are some soils, which, besides a proper mechanical texture 

 and mixture of earths, contain a large proportion of a natural manure 

 which renders them extremely fertile. This is a substance produced 

 by the slow decay of animal and vegetable matter. It can be separated 

 from the other parts of the soil, and has been accurately analysed and 

 described by many of the most experienced chemists, particularly by 

 Fourcroy, Davy, Chaptal, and Theodore de Saussure. (See ' Recherches 

 Chimiques sur la Vegetation,' Paris, 8vo, 1804.) This substance has 

 been called rentable mould ; but, as this is not a very distinct term, 

 we shall, after Thaer and other eminent writers on agriculture, adopt 

 the name of humui when speaking of it. Humus is a dirk, unctuous, 

 friable substance, nearly uniform in its appearance. It is a compound 

 of oxygen, hydrogen, carbon, and nitrogen, which along with certain 

 mineral ingredients, are the elements of all animal and vegetable 

 substances. It is the result of the slow decomposition of organic 

 matter in the earth, and is found in the greatest abundance in rich 

 garden mould, or old neglected dunghills. It varies somewhat in its 

 qualities and composition, according to the substances from which it 

 has been formed and the circumstances attending their decay. By 

 bringing fresh portions of soil to the surface and permitting the 

 access of air to it, this half -decayed vegetable matter is made to undergo 

 still further changes resulting in carbonic acid and other substances in 

 a form adapted to the nourishment of the growing plant. Hence we see 

 the great importance of frequently stirring the surface of the earth 

 between cabbages and other vegetables. 



, We can now readily understand the great importance of humus, 

 and of those rich manures which are readily converted into it when 

 not immediately absorbed by plants. But this vegetable ingredient of 

 the soil has still another property, highly important to fertility : it 

 renders stiff clays porous, and consolidates loose eands. It does so 

 more than lime, or any other earth. Hence a soil with a considerable 

 proportion of humus is much more fertile than the quantity of other 

 substances in its composition would lead one to expect, as we shall see 

 when we come to the analysis of soils of known fertility ; and we see 

 the great advantage of animal and vegetable manures, not only as 

 nourishment to vegetables, but as mechanical improvers of the texture 

 of soils. 



The greatest enemy of humus is stagnant water; it renders it acid 

 and astringent, as we gee in peat ; and soils abounding with vegetable 

 matters, from which water is not properly drained, become sour, as is 

 Tery justly said, and produce only rushes and other useless and 

 unpalatable plants. The remedy is simple and obvious ; drain well, 



and neutralise the acids with lime ; by these means abundant fertility 

 will be restored. 



In very light soils humus is seldom found in any quantity, being too 

 much exposed to the air and rapidly decomposed; the extract is 

 washed through them by the waters, and as they waste manure 

 rapidly, they are called hungry. Such soils are very unprofitable 

 until they are improved and consolidated by clay or marl, which makes 

 them retain the moisture. 



With calcareous earths humus acta well, provided they are pulverised 

 and of sufficient depth. Some chalky soils are rendered very fertile 

 by judicious culture and manuring. 



In order to ascertain the probable fertility of a soil, it is very useful 

 to analyse it and find out the proportion of its component parts. To do 

 this with great accuracy requires the knowledge of an experienced 

 chemist ; but certain steps in the process of analysis may be easily 

 taken by any person possessed of an accurate balance and weights, and 

 a little muriatic acid. For this purpose, some of the soil, taken at 

 different depths, not too near the surface (from four to eight inches, if 

 the soil is uniform in appearance), is dried in the sun till it pulverises 

 in the hand, and feels quite dry : the small stones and roots are taken 

 out, but not minute fibres. A convenient portion of this is accurately 

 weighed : it is then heated in a porcelain-cup, over a lamp or clear 

 fire, and stirred till a chip or straw put in it turns brown. It is then 

 set to cool, and weighed ; the loss of weight is the water, which it is 

 of importance to notice. Some soils, to appearance quite dry, contain 

 a large proportion of water ; others, scarcely any. It is then pulverised 

 and sifted, which separates the fibres and coarser parts. The remainder, 

 again weighed, is stirred in four or five times its weight of pure water ; 

 after standing a few minutes to settle, the water is poured off, and it 

 contains most of the humus and soluble substances. The humus is 

 obtained by filtration, well-dried over the lamp, and weighed. The 

 soluble substances are obtained by evaporating the water ; but, unless 

 there is a decidedly saline taste, this may be neglected. The humus 

 may be further examined by heating it red hot in a crucible and 

 stirring it with a piece of the stem of a tobacco-pipe, when the vege- 

 table part will be consumed, and the earths remain behind ; thus the 

 exact quantity of pure vegetable humus is found. Some muriatic 

 acid, diluted with five times its weight of water, is added to the 

 deposit left after pouring off the water containing the humus and 

 soluble matter : the whole is agitated, and more acid added gradually, 

 as long as effervescence takes place, and until the mixture remains 

 decidedly acid, which indicates that all the calcareous earth is dissolved. 

 Should there be a great proportion of this, the whole may be boiled, 

 adding muriatic acid gradually, till all effervescence ceases ; what 

 remains, after washing it well, is siliceous and argillaceous earth. 

 These are separated by agitation, allowing the siliceous part to settle, 

 which it does in a few seconds. The alumina is poured off with the 

 water, filtrated, heated over the lamp, and weighed, the same with 

 the siliceous sand. The loss of weight is calcareous earth. In this 

 manner, but with greater care and more accurate tests, various soils 

 of known fertility have been analysed, of which we will give a few 

 examples. 



A very rich soil near Drayton, Middlesex, examined by Davy, con- 

 sisted of J of siliceous sand and of impalpable powder, which analysed, 

 was found to be composed of 



Ports. 

 Carbonate of lime ..... 28 



Siliceous earth 32 



Alumina ....... 29 



Animal and vegetable matter . . . 11 



100 



This is a rich sandy loam, probably long and highly manured, fit for 



any kind of produce, and, if deep, admirably fitted for fruit trees. 

 Another good turnip soil, also examined by Davy, consisted of eight 



parts of coarse siliceous sand, and one of fine earth, which, being 



analysed, consisted of 



Ports. 



Carbonate of lime 63 



Silica 15 



Alumina . . . . . . .11 



Oxide of iron 3 



Vegetable and saline matter ... 5 

 Water 3 



100 



This is a very light sandy soil, and owes its fertility to the fine division 

 of the carbonate of lime and the vegetable and saline matter. It may 

 probably have been limed or marled at some time or other. 

 The best loam in France, according to Mr. Tillet, consists of 



Fine siliceous sand 

 Coarse ditto . 

 Carbonate of lime 

 Alumina 



