See also:

• SOGDIANA (Sugdiane, O. Pers. Sughuda)

The subsoil not unfrequently contains materials which are deleterious to the growth of crops, and roots descending into it may absorb and convey these poisonous substances to other parts of the plant or be themselves damaged by contact with them. On this account deeper tillage than usual, which allows of easier penetration of roots, or the carrying out of operations which bring the subsoil to the See also:

• SURFACE

The oxygen of the air may also bring about chemical changes which result in the See also:

• PRODUCTION (Lat. productionem, from producere, to pro-duce)

Lastly there is a form " soil," used by agriculturists, of the feeding and fattening of See also:

• CATTLE (Norman Fr. catel, from Late Lat. capitale, wealth or property, a word applied in the feudal system to movable property and particularly to live stock, and surviving in its wider meaning as " chattel " or " chattle ")

Quality of Soil.—The See also:

• GOOD, JOHN MASON (1764-1827)

Soil whose temperature remains See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

Even in the soils which farmers speak of as stiff clays it is rarely present to the extent of more than I or 2 °'°. The word " clay " used in the agricultural sense denotes a sticky intractable material which is found to consist of exceedingly fine particles (generally less than .005 mm. in See also:

• DIAMETER (from the Cr. &a, through, µErpov, measure)

Few of the commonly cultivated crops can live in a soil consisting mainly of humus. From the above account it will be understood that not one of the four chief soil constituents is in itself of value for the growth of crops, yet when they are mixed, as they usually are in the soils met with in nature, one corrects the deficiencies of the other. A perfect soil would be such a blend of sand, clay, chalk and humus as would contain sufficient clay and humus to prevent drought, enough sand to render it pervious to fresh air and prevent water-logging, chalk enough to correct the tendency to acidity of the humus present, and would have within h. various substances which would serve as food-materials to the crops: Generally speaking, soils containing from 30 to' 50% of clay and 5o to 6o%, of sand with an adequate amount of vegetable residues prove the most useful for ordinary farm and See also:

• GARDEN (from O. Fr. garden, mod. Fr. jardin; this, like our words " garth," a paddock attached to a building, and " yard," comes from a Teutonic word for an enclosure which appears in Gothic as gards and O. H. Ger. gart, cf. Dutch gaarde and Ger. .garten)

8 „ 19 Clay below .004 mm. . 8 „ 40 ,, The See also:

• PORE

gen. Acid. See also:

• WHEAT
• WHEAT (Triticum)

18 „ •32 Potash . . . • 19 „ • 57 Carbonate of Lime .23 „ I.22 „ Since the dry See also:

• WEIGHT

At present it is not possible to determine with accuracy the amount of immediately available plant food-constituents in a soil: no doubt the various See also:

• SPECIES

In the case of See also:

• FAIR

Plants have been found to See also:

• WITHER, GEORGE (1588-1667)

A loose layer of earth spread over the surface of the soil acts in the same way, and a similarly effective mulch may be prepared by hoeing the soil, or stirring it to a depth of one or two inches with harrows or other implements. The See also:

• HOE (through Fr. houe from O.H.G. houwd, mod. Ger. Haue; the root is seen in " hew," to cut, cleave; the word must be distinguished from " hoe," promontory, tongue of land, seen in place names, e.g. Morthoe, Luton Hoo, the Hoe at Plymouth, &c. ; this is t
• HOE, RICHARD MARCH (1812-1886)

To prevent this various implements, such as disk harrows and specially constructed rollers, may be used to consolidate the upper stirred portion of the soil and place it in close capillary relationship with the See also:

• LOWER

Much of the work carried On by these organisms is not clearly understood; there are, however, certain processes which have been extensively investigated and to these it is necessary to refer. It has been found by experiment that the nitrogen needed by practically all farm crops except leguminous ones is best supplied in the form of a nitrate; the rapid effect of nitrate of soda when used as a See also:

• TOP (cf. Dan. top, Ger. Topf, also meaning pot)

In the first place an adequate temperature is essential; at 5° or Er' C. (40°–43° F.) the process is stopped, so that it does not go on in winter. In summer, when the temperature is about 24° C. (75° F.), nitrification proceeds at a rapid rate. The organisms do not carry on their work in soils deficient in air; hence the process is checked in water-logged soils. The presence of a base such as lime or magnesia (or their carbonates) is also essential, as well as an adequate degree of moisture: in dry soils nitrification ceases. It is the business of the farmer and gardener to promote the activity of these organisms by good tillage, careful drainage and occasional application of lime to soils which are deficient in this substance. It is only when these conditions are attended to that decay and nitrification of dung, See also:

• GUANO (a Spanish word from the Peruvian huanu, dung)

These organisms reduce nitrates to nitrites and finally to ammonia and gaseous free nitrogen which escapes into the See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

This is due to the nitrogenous root residues left in the land. Upon the roots of leguminous plants characteristic swollen nodules or tubercles are present. These are found to contain large numbers of a bacterium termed Bacillus radicicola or Pseudomonas radicicola. The bacteria, which are present in almost all soils, enter the root-hairs of their See also:

• HOST

In this manner organisms obtained from red clover can be grown and applied to the seed of red clover; and similar inoculation can be arranged for other species, so that an application of the bacteria most suited to the particular crop to be cultivated can be assured. In many, cases it has been found that inoculation,. whether of the soil or of the seed, has not made any appreciable difference to the growth of the crop, a result no doubt due to the fact that the soil had already contained within it an abundant supply of suitable organisms. But in other instances greatly increased yields have been obtainedwhere inoculation has been practised. More or less pure cultures of the nitrogen-fixing bacteria belonging to the Azotobacter group have been tried and recommended for application to poor land in order to provide a cheap supply of nitrogen. The application of pure cultures of bacteria for improving the fertility of the land is still in an experimental stage. There is little doubt, however, that in the near future means will be devised to obtain the most efficient work from these minute organisms, either by special artificial cultivation and subsequent application to the soil, or by improved methods of encouraging their healthy growth and activity in the land where they already exist. Improvement of Soils.—The fertility of a soil is dependent upon a number of factors, some of which,. such as the addition of fertilizers or manures, increase the stock of available food materials in the soil (see MANURE), while others, such as application of clay or humus, chiefly influence the fertility of the land by improving its physical texture. The chief processes for the improvement of soils which may be discussed here are: liming, claying and marling, warping, paring and burning, and green manuring. Most of these more or less directly improve the land by adding to it certain plant food constituents which are lacking, but the effect of . each process is in reality very complex. In the majority of cases the good results obtained are more particularly due to the setting free of " dormant " or " latent " food constituents, and to the amelioration of the texture of the soil, so that its aeration, drainage, temperature and water-holding capacity are altered for the better. The material which chemists See also:

• CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

Carbonate of lime is also a constituent to a greater or lesser extent in almost all soils. 'In certain sandy soils and' in a few stiff clays it may amount to less than 1%, while in others in See also:

• LIMESTONE

The lime causes the minute See also:

• SEPARATE

Land which contains less than about 1% of lime usually needs the addition of this material. The particular form in which lime should be applied for the best results depends upon the nature of the soil. In practice the proximity to chalk pits or lime kilns, the cost of the lime and cartage, will determine which is most economical. Generally speaking light poor lands deficient in organic matter will need the less caustic form or chalk, while See also:

• QUICK

It contains a certain amount of unaltered caustic lime and slacked lime, along with sulphates and sulphides of lime, some of which have an evil odour. As some of these sulphur compounds have a poisonous effect on plants, gas-lime cannot be applied to land directly without great See also:

• RISK

In some cases as little as 40 loads per acre have been used with benefit, in others 18o loads have not been too much. The material is dug from neighbouring pits or sometimes from the fields which are to be improved, and applied in autumn and winter. When dry and in a crumbly state it is harrowed and spread and finally ploughed in and mixed with the soil. On some of the strongest land it was formerly the practice to add to and plough into it burnt clay, with the See also:

• OBJECT

The turf is taken off either with the See also:

• BREAST (a word common to Teutonic languages, cf. the Ger. Brust, possibly connected with an O. Sax. brustian, to bud)

Many of the mineral plant food-constituents locked up in the coarse herbage and in the upper layers of the soil are made immediately available to crops. The chief disadvantage is the loss of nitrogen which it entails, this See also:

• ELEMENT (Lat. elementum)

Green manures are crops which are grown especially for the purpose of ploughing into the land in a green or actively growing state. The See also:

• OMEN (a Latin word, either connected with os, mouth, or more probably with auris (Gr. ois, ear; apparently, meaning " a thing heard " or " spoken ")

The best time for the operation appears to be See also:

• LATE

Some sands contain as much as 50% of air of nearly the same composition as atmospheric air. The oxygen, however, decreases with the depth, while the carbon dioxide increases. 351 Among the most noteworthy workers at the problems involved in the question of the influence of soil in the production of disease we find von Foder, See also:

• PETTENKOFER, MAX JOSEPH VON (1818-1901)

In the laboratory See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

Certain disease-producing organisms, such as the bacillus of See also:

• TETANUS (from Gr. rei:vw, I stretch, on account of the tension of the fibres of the affected muscles), or LOCKJAW