The Temuka Leader TUESDAY, FEBRUARY 26, 1884. WHAT FARMERS OUGHT TO KNOW.

Temuka Leader, Issue 1145, 26 February 1884, Page 2

The Temuka Leader TUESDAY, FEBRUARY 26, 1884. WHAT FARMERS OUGHT TO KNOW.

AGRICULTURAL CHEMISTRY. IV. Soil, To continue our consideration of soil. The fertility of land depends on two things—(l) Its chemical composition ; (2) its mechanical texture. Before proceeding to raise a crop it is necessary to know that the land contains the essential elements of that crop ; thus, if we wish to produce a wheat crop, we know that silica must be present in the soil in comparatively large quantities, so that the crop may reach maturity and be a good yield ; if turnips are to be grown: potash, lime, soda, are necessary constituents ; if,barley : phosphoric acid, silica ; if outs; nitrogen matters ; if potatoes : potash, magnesia, soda, sulphuric acid. These of course do not comprise the whole composition of the respective crops, only the mineral matters present in most abundance. If the soil does not contain the various mineral constituents required by vegetable growth, then the land cannot be said to be fertile, nor will the crop be what it could and should be. When land gets exhausted, or, in other words, when so much of the essential components of vegetable growth is removed that it cannot supply grain with its necessary food, then these mineral and other matters that have been removed must be supplied to the land to make up the deficiency. Hence the employment of manures on worked out land. The mechanical texture of a soil is also a very important item in judging fertility,, and a knowledge of this can be gained by experience only, not by chemical analysis. We saw before that soil was chiefly composed of silica, alumina, carbonate of lime, potash, soda, magnesia, sulphur and chlorine. We now proceed to point out some of the more important properties of these substances and their use in soil. Silica. Silica (the oxide of silicon or silicum) forms a very large proportion of rocks and minerals. Sand is composed principally of this oxide ; in the white variety we see almost pure silica, in (he gray and red we hare it colored with oxido of iron, Sand, we know, is a bard gritty substance, and insoluble in water. In this state it is evident that it is almost useless as plant food, for it must be remembered that plants take up their mineral constituents in solution in water. We would naturally expect that some modification of silica, other than sand, must exist, for it is an essential component of wheat, barley, etc. And so there does. Silica is found, besides in the insoluble condition, also in a soluble one ; and, furthermore, the one plays just about as important a part as the other. The soluble variety is part of the direct food of many of the crops, while the insoluble one is one of the greatest acids in forming soil fit for agriculture, by improving its mechanical texture. Silica is found mostly in the straw of grain, as for instance in wheat, oats, barley, etc. One of the otfices of this glass-like compound is to strengthen the stem of the plant itself, thus making it more capable of bearing the weight of the grain. So important is the presence of various mineral substances in plants that it has given rise to a classification, based on the relative preponderance of any particular mineral in a plant. Thus we have “ silica ” plants, “ lime” plants, “ potash” plants. Alumina. Alumina (oxide of aluminum) is the chief constituent of clay. It combines with silica to form a salt, called silicate of alumina, silica playing ihe part of an acid, and alumina that of a base or alkali, described in a former article. This salt is pure clay. Colouring matter, however, is generally present, due to the oxide of iron mixed up with the clay. Clay is a smooth plaslic substance ; when wetted it can be made to assume any shape, and then dried it still remains that shape. One of the most important properties of clay is its power of retaining and holding water and salts. Clay, when rain falls, receives the water and holds it with a firm grasp against evaporation ; thus it takes much longer for drought to effect a clayey soil than a sandy one, or one with li .lccrno clay in it. Again, when manure is placed on land the rain soon dissolves out the soluble salts in it, and carries them into the ground ; were it not for the retentive power of clay the water, laden with valuable plant food, would soon trickle down into the sub-soil and below- it, where some of the salts would be deposited, and thus be lost to the soil or cultivable portion of the earth. Another property of clay is its power—like that of humus—to absorb and retain ammonia. OXIDES of iron. Three oxides of iron are also prevailing components of soil. Their names are,

protoxide (or the oxide that contains onealone of oxygen to the one of iron), sesquioxide (or that containing one and a-half times as much oxygen as iron) and the black or magnetic oxide. Now, each of these compounds gives rise to a different colour, and from this we can understand how soaie green clays turn brown and red. The protoxide gives rise to the green shades, sesquioxide to the brown reddish tints, and the magnetic to the black colour. Now, the protoxide contains the smallest amount of oxygen, and it has a tendency to absorb the gas. This it can do easily when exposed to air, and from the piotoxide it changes to the sesquioxide. But the protoxide is green and the sesquioxide red, so the colour changes also. The lowest oxide of iron possesses such a stroDg, tendency to absorb more oxygen that salts kept in the laboratory well bottled, are under- j going change, and if let stand long enough the whole solution becomes a higher salt. The magnetic oxide is also called the black, owing to its colour, which of course it imparts to the soil containing it. We can thus see how thesy three compounds of iron affect the soil in the matter of colour, and hew they tend to change their chemical composition, thus producing different tints. They have the power of absorbing ammonia from the atmosphere (like clay and humus). The red oxide appears to be productive of good in the soil, while the blue is not conducive to the growth of vegetation. The remedy for a blue or green coloured soil, is thus clear : to turn it over to the action of the atmosphere, the oxygen of which will soon convert the injurious green into the beneficial red compound. CARBONATE OF LIME AND LIME. \Ve have already seen, firstly that limestone or chalk is carbonate of lime—that is, a chemical combination of carbonic acid gas and lime ; secondly, that when limestone is fired carbonic acid is driven off and the rdmaining constituent, lime, is left ; thirdly, that in water, lime and carbonic acid gas can be made to unite, thus forming limestone. Having fired limestone, suppose, instead of adding carbonic acid to the lime produced, we add water, what takes place? The mixture rises in temperature, swells, cracks, steams, and finally falls as white powder. This is slaking lime. All these various performances are the result of the chemical union of water and lime. In a previous article, instances were quoted, shewing the liberation of heat when two compounds entered into chemical combination. The bulk is greater because of the absorption of water. Lime performs several functions in toil. It is a direct food of many plants, it corrects acidity, it turns up excess of organic matter, it helps germination by the liberation of heat when uniting with water and carbonic acid present in the soil, its uses, however, we will discuss more in detail under the heading of manures. It is a very essential constituent of ro6t and leguminous crops. The ash of the following crops, contains respectively the annexed percentage amount of lime. Swedes 11.82, yellow turnips 9.44 green top white turnips 6.73, barley straw about 9, pea aboht 6, oat straw about 8, wheat from 2to 4. It will be noted that these figures are the percentage amount of lime present in the ash. From these results some idea may be got of the value of liming land for the purpose of affording the plant direct food, not to speak of the many beneficial qualities this compound has on the land itself. Limestone itself is insoluble in water, and lime is. Little good can accrue from the application of limestone to land, if it is applied for any purpose, it should be in a state of exceedingly fine division. MAGNESIA, POTASH, SODA. These are three compounds that are essential to the growth of various plants, The two first have not yet been generally applied in manures, the third is applied in the form of common salt. PHOSPHORIC ACID. Phosphoric acid is a very necessary constituent in a number of plants. It oocurs generally as a phosphate. There are several phosphates of lime, some insoluble in water, others soluble. Superphosphate is a soluble one, and is prepared from bones, which contain the insoluble compound. It is essential in the food of man, to form bone, and thus vegetables containing a large quantity of it are said to be bone forming. This is a most important compound and will be considered at greater length with the manures. (To be Continued.)