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century B.C . The valley of the Zerafshan about Samarkand retained even in the middle ages the name of the Soghd of Samarkand . Arabic geographers reckon it as one of the four fairest districts in the See also:

WORLD

world . substance which is stirred or tilled by implements such as ploughs and spades . Below this is the subsoil . The See also:

SOIL

soil through being acted upon by the See also:

air, See also:

HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat, See also:

frost and other agencies usually consists of finer particles than those comprising the bulk of the subsoil . It contains more roots, and as a See also:

RULE

rule, is darker in See also:

COLOUR (Lat. color, connected with celare, to hide, the root meaning, therefore, being that of a covering)

colour than the subsoil on See also:

account of the larger proportion of decaying See also:

VEGETABLE

vegetable See also:

MATTER

matter See also:

PRESENT

present in it: it is also looser in texture than the subsoil . 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

surface, must always be carefully considered .

At first sight few natural materials appear to be of less See also:

INTEREST

interest than the soil; yet its importance is See also:

MANIFEST (Lat. manifestus, clear, open to view)

manifest on the slightest reflection . From it, directly or indirectly, are obtained all See also:

food materials needed by See also:

man and beast . The inorganic materials within it See also:

SUPPLY (through Fr. from Lat. supplere, to fill up)

supply some of the See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief substances utilized by See also:

PLANTS

plants for their development and growth, and from plants animals obtain much of their sustenance . Origin of the Soil.—It is a matter of See also:

COMMON

common observation that stones of monuments, walls or buildings which are exposed to the air sooner or later become eaten away or broken up into small fragments under the See also:

INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence of the See also:

WEATHER (O. Eng. weder; the word is common to Teutonic languages; cf. Du. weder, Dan. veir, Icel. ve8r, and Ger. Wetter and Gewitter, storm; the root is wa- to blow, from which is derived " wind ")

weather . This disintegration is brought about chiefly by changes in temperature, and by the See also:

ACTION

action of the See also:

RAIN (O.E. regn; the word is common to Teutonic languages, cf. Ger. Regen, Swed. and Dan. regn; it has been connected with Lat. rigare, to wet, Gr. 13pixeav)

rain, the See also:

OXYGEN (symbol 0, atomic weight 16)

oxygen, and the See also:

CARBON (symbol C, atomic weight 12)

carbon dioxide of the air . During the daytime the surface of the See also:

stone may become very warm, while at See also:

NIGHT

night it is speedily cooled . Such alterations in temperature produce strains which frequently result in the chipping off of small fragments of the material composing the stone . Moreover the rain penetrates into the small interstices between its particles and dissolves out some of -the materials which bind the whole into a solid stone, the surface then becoming a loose powdery See also:

mass which falls to the ground below or is carried away by the See also:

wind . The action of frost is also very destructive to many stones, since the See also:

WATER

water within their cracks and crannies expands on freezing and splits off small pieces from their surfaces . In the See also:

case of See also:

lime-stones the carbon dioxide of the air in association with rain and See also:

dew eats into them and leads to their disintegration . 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)

production of soluble substances removable by rain, the insoluble parts being See also:

LEFT

left in a loosened See also:

state . These " weathering " agents not only See also:

ACT (Lat. actus, actum)

act upon stones of buildings, but upon rocks of all kinds, reducing them sooner or later into a more or less See also:

FINE

fine See also:

POWDER (through O. Fr. puldre, modern poudre, from Lat. pulvis, pulveris, dust)

powder .

The See also:

WORK

work has been going on for ages, and the finely comminuted particles of rocks See also:

FORM (Lat. forma)

form the See also:

main bulk of the soil which covers much of the See also:

earth's surface, the See also:

REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest of the soil being composed chiefly of the remains of roots and other parts of plants . If the whole of the soil in the See also:

BRITISH

British Islands were swept into the See also:

sea and the rocks beneath it laid See also:

BARE

bare the surface of the See also:

COUNTRY (from the Mid. Eng. contre or contrie, and O. Fr. cuntree; Late Lat. contrata, showing the derivation from contra, opposite, over against, thus the tract of land which fronts the sight, cf. Ger. Gegend, neighbourhood)

country would ultimately become covered again with soil produced from the rocks by the weathering processes just described . Moreover where there was no transport or See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of the soil thus produced it would necessarily show some similarity in See also:

composition to the See also:

rock on which it rested . The soils overlying red See also:

SANDSTONE

sandstone rocks would be reddish and of a sandy nature, while those overlying See also:

CHALK

chalk would be whitish and contain considerable amounts of lime . In many parts of the country soils exhibiting such relationships, and known as sedentary soils, are prevalent, the transition from the soil to the rock beneath being plainly visible in sections exposed to view in railway cuttings, quarries and other excavations . The upper layer or soil proper consists of material which has been subjected See also:

SWINE

swine, See also:

sus . " To See also:

sully," to besmirch, to See also:

COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover with " mire " (0 . Eng . sol cf . Ger siihkx) is a quite distinct word . 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 ")

cattle with See also:

green food such as vetches . This is from O .

Fr. saoler, saouler, mod. sotller, See also:

Lat. satullsts; full-fed (satur, satiated, satis, enough) . to ages of weathering; the bulk of it is composed of finely comminuted particles of See also:

sand, See also:

clay and other minerals, among which are imbedded larger or smaller stones of more refractory nature . On descending into the substratum the finer material decreases and more stones are met with; farther down are seen larger fragments of unaltered rock closely packed, and this brash or See also:

RUBBLE

rubble grades insensibly into the unbroken rock below . In many districts the soil is manifestly unconnected in origin with the rock on which it rests, and differs from it in colour, composition and other characters . There are transported or See also:

DRIFT (from "drive ")

drift soils, the particles of which have been brought from other areas and deposited over the rocks below . Some of the stiff See also:

boulder See also:

CLAYS, PAUL JEAN (1819-1900)

clays or " till so prevalent over parts of the north of See also:

England appear to have been deposited from See also:

ICE (a word common to Teutonic languages; cf. Ger. Eis)

ice sheets during the glacial See also:

period . Perhaps the See also:

MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of drift soils, however, have been moved to their present position by the action of the water of See also:

rivers or the sea . As fast as the rock of a cliff is weathered its fragments are washed to the ground by the rain, and carried down the slopes by small streams, ultimately finding their way into a See also:

RIVER

river along which they are carried until the force of the water is insufficient to keep them in suspension, when they become deposited in the river See also:

bed or along its See also:

banks . Such river-transported material or See also:

ALLUVIUM

alluvium is common in all river valleys . It is often of very mixed origin, being derived from the detritus of many kinds of rocks, and usually forms soil of a fertile See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character . Quality of Soil.—The See also:

GOOD, JOHN MASON (1764-1827)

good or See also:

BAD, BCD

bad qualities of a soil have reference to the needs of the crops which are to be grown upon it, and it is only after a See also:

CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration of the requirements of plants that a clear conception can be formed of what characters the soil must possess for it to be a suitable See also:

MEDIUM

medium on which healthy crops can be raised . In the first See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place, soil, to be of any use, must be sufficiently loose and porous to allow the roots of plants to grow and extend freely .

It may be so compact that See also:

root development is checked or stopped altogether, in which case the plant suffers . On the other See also:

hand it should not be too open in texture or the roots do not get a proper hold of the ground and are easily disturbed by wind: moreover such soils are liable to See also:

BLOW, JOHN (1648-1708)

blow away, leaving the underground parts exposed to the air and drought . The roots like all other parts of plants contain See also:

PROTOPLASM

protoplasm or living material, which cannot carry on its functions unless it is supplied with an adequate amount of oxygen: hence the See also:

NECESSITY (Lat. necessitas)

necessity for the continuous circulation of fresh air through the soil . If the latter is too compact or has its interstices filled with carbon dioxide See also:

gas or with water—as is the case when the ground is water-logged--the roots rapidly See also:

die of suffocation just as would an See also:

animal under the same conditions . There is another point which requires See also:

ATTENTION (from Lat. ad-tendo, await, expect; the condition of being " stretched " or " tense ")

attention . Plants need very considerable amounts of water for their See also:

NUTRITION

nutrition and growth; the water-holding capacity is, therefore, important . If the soil holds too much it becomes water-logged and its temperature falls below the point for healthy growth, at any See also:

RATE

rate of the kinds of plants usually cultivated on farms and in gardens . If it allows of too See also:

FREE

free drainage drought sets in and the plants, not getting enough water for their needs, become stunted in See also:

SIZE

size . Too much water is bad, and too little is equally injurious . In addition, the temperature of the soil largely controls the yield of crops which can be obtained from the See also:

LAND

land . Soil whose temperature remains See also:

low, whether from its northerly aspect or from its high water content or other cause, is unsatisfactory, because the germination of seeds and the See also:

general See also:

LIFE

life processes of plants cannot go on satisfactorily except at certain temperatures well above freezing-point . A good soil should be deep to allow of extensive root development and, in the case of arable soils, easy to work with implements .

Even when all the conditions above mentioned in regard to texture, water-holding capacity, aeration and temperature are suitably fulfilled the soil may still be barren: plant food-material is needed . This is usually present in abundance although it may not be available to the plant under certain circumstances, or may heed to be replenished or increased by additions to the soil of See also:

MANURES

manures or fertilizers (see MANURE) . Chief Constituents of the Soil.—An examination of the soil shows it to be composed of a vast number of small particles of sand, clay, chalk and humus, in which are generally imbedded larger or smaller stones . It will be useful to consider the nature of the four chief constituents just mentioned and their bearing upon the texture, water-holding capacity and other characters which were referred to in the previous See also:

section . Sand consists of grains of See also:

QUARTZ

quartz or See also:

flint, the individual particles of which are large enough to be seen with the unaided See also:

eye or readily See also:

FELT (cognate with Ger. Filz, Du. vilt, Swed. and Dan. fill; the root is unknown; the word has given Med. Lat. filtrum, " filter ")

felt as gritty grains when rubbed between the See also:

FINGER

finger and thumb . When a little soil is shaken up with water in a See also:

TUMBLER

tumbler the sand particles rapidly fall to the bottom and form a layer which resembles See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary sand of the seashore or river banks . Chemically pure sand is See also:

SILICON [symbol Si, atomic weight 28.3 (0= 16)]

silicon dioxide (SiO2) or quartz, a clear transparent See also:

glass-like See also:

MINERAL

mineral, but as ordinarily met with, it is more or less impure and generally coloured reddish or yellowish by See also:

OXIDE

oxide of See also:

IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron . A soil consisting of sand entirely would be very loose, would have little capacity to retain water, would be liable to become very hot in the daytime and cool at night and would be quite unsuitable for growth of plants . The See also:

TERM

term clay is often used by chemists to denote hydrated silicate of alumina (Al203.2SiO2.2H20), of which See also:

KAOLIN

kaolin or See also:

CHINA

china clay is a fairly pure form . This substance is present in practically all soils but in comparatively small amounts . 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)

diameter) of sand and other minerals derived from the decomposition of rocks, with a small amount of silicate of alumina .

The See also:

PECULIAR

peculiar character which clay possesses is probably due not to its chemical composition but to its See also:

PHYSICAL

physical state . When wet it becomes sticky and almost impossible to move or work with See also:

FARM

farm implements; neither air nor water can penetrate freely . In a dry state it becomes hard and bakes to a See also:

BRICK (derived according to some etymologists from the Teutonic bricke, a disk or plate; but more authoritatively, through the French brique, originally a " broken piece," applied especially to bread, and so to clay, from the Teutonic brikan, to break)

brick . It holds water well and is consequently See also:

COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold, needing the application of much heat to raise its temperature . It is obvious, therefore, that soil composed entirely of clay is as useless as pure sand so far as the growth of crops upon it is concerned . Chalk consists, when quite pure, of See also:

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

calcium carbonate (CaCO3), a See also:

white solid substance useful in small amounts as a plant food-material, though in excess detrimental to growth . Alone, even when broken up into small pieces, it is unsuitable for the growth of plants . Humus, the remaining constituent of soil, is the term used for the decaying vegetable and animal matter in the soil . A good See also:

ILLUSTRATION

illustration of it is See also:

PEAT (possibly connected with Med. Lat. petia, pecia, piece, ultimately of Celtic origin; cf. O. Celt. pet, O. Ir. pit, Welsh peth, portion)

peat . Its water-holding capacity is See also:

GREAT

great, but it is often See also:

ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid, and when dry it is See also:

LIGHT

light and incapable of supporting the roots of plants properly . 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)

garden crops; such blends are known as " foams,” those in which clay predominates being termed clay See also:

LOAN (adapted from the Scandinavian form of a word common to Teutonic languages, cf. Swed. Mn, Icel. lan, Dut. leen; the O.E. laen appears in " lend," the ultimate source is seen in the root of Gr. Xeiaecv and Lat. linquere, to leave)

loan's, and those in which the sand predominates sandy foams . " Stiff clays " contain over 5o% of clay; " light sands " have less than io % . In the See also:

MECHANICAL

mechanical See also:

ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis of the soil, after separation of the stones and fine See also:

GRAVEL, or PEBBLE BEDS

gravel by means of See also:

SIEVES

sieves, the See also:

REMAINDER, REVERSION

remainder of the finer earthis subjected to various processes of sifting and deposition from water with a view of determining the relative proportions of sand, silt and clay present in it . Most of the material termed " sand " in such analyses consists of particles ranging in diameter from •5 to .05 mm., and the " silt " from .05 to .005 mm., the " clay " being composed of particles less than .005 mm. in diameter . The proportional amount of these materials in a sandy soil on the Bagshot beds and a stiff See also:

Oxford clay is given below: Soil on Soil on Bagshot Beds . Oxford Clay . Coarse sand 1—•2 mm . . 32 % II % Fine sand .2–•04 mm . 40 ,' I1] ,, Silt •04–•01 mm . I2 „ 19 Fine silt .01–•004 mm . 8 „ 19 Clay below .004 mm . . 8 „ 40 ,, The See also:

PORE

pore-space within the soil, i.e. the space between the particles composing the soil, varies with the size of these particles and with the way they are arranged or packed .

It is important, since upon it largely depends the See also:

MOVEMENT

movement of air and water in the land . It is generally from 30 to 50 % of the See also:

TOTAL

total See also:

VOLUME

volume occupied by the soil . Where the soil grains are quite free from each other the smaller grains tend to fill up the spaces between the larger ones; hence it might be concluded that in clays the amount of pore-space would be less than in coarser sands . This is the case in " puddled'' clays. but in ordinary clay soils the excessively See also:

minute particles of which they largely consist tend to form See also:

groups of comparatively large composite grains and it is in such natural soils that the pore-space is largest . Chemical Composition of the Soil.—It has been found by experiment that plants need for their nutritive See also:

PROCESS

process and their growth, certain chemical elements, namely, carbon, See also:

HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen, oxygen, See also:

NITROGEN [symbol N., atomic weight 14.01, 0=16]

nitrogen, See also:

SULPHUR

sulphur, See also:

PHOSPHORUS (Gr. 4ws, light, sPEpety, to bear)

phosphorus, See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium, See also:

MAGNESIUM [symbol Mg, atomic weight 24.32 (0 = 16)]

magnesium, calcium and iron . With the exception of the carbon and a small proportion of the oxygen and nitrogen, which may be partially derived from the air, these elements are taken from the soil by crops . The following table shows the amounts of the chief constituents removed by certain crops in lb per See also:

acre: See also:

CROP (a word common. in various forms, such as Germ. Kropf, to many Teutonic languages for a swelling, excrescence, round head or top of anything; it appears also in Romanic languages derived from Teutonic, in Fr. as troupe, whence the English " crupper "

Crop . Nitro- Phos- Potash . Lime . Mag- Nitro- phoric nesia . gen . Acid .

See also:

Wheat . . . lb lb lb lb lb 5o 21 29 9 7 Meadow See also:

hay 49 12 51 32 14 Turnips to 33 149 74 9 Mangels . . 149 53 300 43 42 Plants also remove from the soil silicon, See also:

SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium, See also:

CHLORINE (symbol Cl, atomic weight 35`46 (0=16)

chlorine, and other elements which are, nevertheless, found to be unessential for the growth and may therefore be neglected here . Leguminous crops take some of the nitrogen which they require from the air, but most plants obtain it from the nitrates present in the soil . The sulphur exists in the soil chiefly in the form of sulphates of magnesium, calcium and other metals; the phosphorus mainly as See also:

PHOSPHATES

phosphates of calcium, magnesium and iron; the potash, soda and other bases as silicates and nitrates; calcium and magnesium See also:

CARBONATES

carbonates are also common constituents of many soils . In the ordinary chemical analyses of the soil determinations are made of the nitrogen and various carbonates present as well as of the amount of phosphoric acid, potash, soda, See also:

MAGNESIA

magnesia and other components soluble in strong hydrochloric acid . Below are given examples of the analyses of a poor sandy soil and an ordinary See also:

LOAM (O.E. lam; the word appears in Dut. leem and Ger. Lehm; the ultimate origin is the root lai-, meaning " to be sticky," which is seen in the cognate " lime," Lat. limus, mud, clay)

loam Poor sandy Soil Loam or on Bagshot Beds . See also:

LIAS

Lias . Nitrogen t9 % 17 % Phosphoric acrid . . . 18 „ •32 Potash . . .

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

WEIGHT

weight of the first See also:

FOOT

foot of soil over an acre is about 4,000,000 lb the poor sandy soil contains within it: Nitrogen 7,600 lb Phosphoric acid . . . 7,200 Potash 7,600 „ Lime 9,200 From the figures given previously of the amount of nitrogen, potash and phosphoric acid removed by a wheat or mangel crop it would appear that this soil has enough of these ingredients in it to yield many such crops; yet experience has shown that these crops cannot be grown on such a poor sandy soil unless manures containing phosphates, potash and nitrogen are added . Many attempts have been made to correlate the results of the analyses of a soil with its known cropping See also:

POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power, but there is yet much to be learnt in regard to these matters . A great proportion of the food constituents which can be extracted by strong hydrochloric acid are not in a See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition to be taken up by the roots of plants; they are present, but in a " dormant " state, although by tillage and weathering processes they may in See also:

time become "avail-able " to plants . Analyses of this character would appear to indicate the permanent productive capacity of the soil rather than its immediate power of growing a crop . Soils containing less than .25 % of potash are likely to need See also:

SPECIAL

special application of potash fertilizers to give good results, while those containing as much as •4 or •5"% do not usually See also:

RESPOND

respond to those manures . Where the amount of phosphoric acid (P2Os) is less than *05% phosphatic manures are generally found to be beneficial; with more than •1 % present these fertilizers are not usually called for except perhaps in soils containing a high percentage of iron compounds . Similarly soils with' less than '.t % of nitrogen are likely to be benefited by applications of nitrogenous „manures . Too much stress, however, cannot be laid upon these figures, since the fertility of a soil is very greatly influenced by texture and physical constitution, perhaps more so by these factors than by chemical composition . 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

species of plants differ somewhat in their power of absorbing these even from the same soil . The method introduced by See also:

Dyer of dissolving out the mineral constituents of th” soil with a 1% solution of citric acid, which represents about the See also:

AVERAGE

average acidity of the roots of most common plants, yields better results .

In the case of arable soils, where the amount of phosphoric acid determined by this method falls below •ot %, phosphatic manuring is essential for good crops . The writer has found that many pasture soils containing less than .025 or .03%, respond freely to applications of phosphates; probably in such cases even the weak acid iscapable of dissolving out phosphates from the humus or other compounds which yield little or none to the roots of See also:

GRASSES

grasses and clovers . In soils where the potash available to citric acid is less than '•005 %, kainit and other potash fertilizers are needed . Water in the Soil.—The importance of an adequate supply of water to growing crops cannot well be over-estimated . During the life of a plant there is a continuous stream of water passing through it which enters by the root-hairs in the soil and after passing along the See also:

STEM (O. Eng. staefn, stemn, cf. Du. stain, Ger. Stamm, &c., probably related to " staff ")

stem is given off from the stomata of the leaves into the open air above ground . It has been estimated that an acre of See also:

CABBAGE

cabbage will absorb from the land and transpire from its leaves more than ten tons of water per See also:

day when the weather is fine . In addition to its usefulness in maintaining a turgid state of the See also:

young cells without which growth cannot proceed, water is itself a plant food-material and as absorbed from the soil contains dissolved in it all the mineral food constituents needed by plants for healthy nutrition . Without a sufficient supply plants remain stunted and the crop yield is seriously reduced, as we see in dry seasons when the rainfall is much below the average . If one condition is more necessary than another for good crops it is a suitable supply of water, for no amount of manuring or other treatment of the soil will make up for a deficient rainfall . The amount needed for the most satisfactory nutrition varies with different plants . In the case of See also:

FAIR

fair average farm crops it has been shown that for the production of one•ton of dry matter contained in them from 300 to 500 toils of water has been absorbed and utilized by the plants . This may be more than the rainfall, in which case See also:

IRRIGATION (Lat. in, and rigare, to water or wet)

irrigation or special See also:

CONTROL (Fr. contrdle, older form contre rolle, from Med. Lat. contra-rotulus, a counter roll or copy of a document used to check the original; there is no instance in English of the use of " control " in this, its literal, meaning)

control of the water supply may be necessary .

The water-holding capacity of a soil depends upon the amount of free space between the particles of which it is composed into which water can enter . In most cases this amounts to from 3o to 5o% of the volume of the soil . When the pore-space of the soil is filled' with water it becomes water-logged and few plants can effect absorption by their roots, under such conditions . The root-hairs die from want of air, and the whole plant soon suffers . See also:

FIELDS, JAMES THOMAS (1817-1881)

Fields of wheat and other cereals rarely recover after a See also:

WEEK (from A.S. wicu, Germanic *wikon, probably=change, turn)

week's submergence, but orchards and many trees when at rest in See also:

winter withstand a flooded or water-logged condition of the soil for two or three See also:

WEEKS, EDWIN LORD (1849-1903)

weeks without damage . The most satisfactory growth is maintained when the amount of water present is not more than 40 to 6o% of what would saturate it . Under such conditions each particle of soil is surrounded by a thin film of water and in the pore-space. air can freely circulate . It is from such films that the root-hairs absorb all that plants require for their growth . The movement of water into the root-hairs is brought about by the osmotic action of certain salts in their See also:

CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell-See also:

sap . Crops are, however, unable to absorb all the water present in the soil, for when the films become very thin they are held more firmly or cling with more force to the soil particles and resist the osmotic action of the root-hairs . Plants have been found to See also:

WITHER, GEORGE (1588-1667)

wither and die in sandy soils containing II % of water, and in clay soils in which there was still present 8% of water . When a See also:

long glass See also:

TUBE (Lat. tuba)

tube open at both ends is filled with soil and one end is dipped in _a shallow See also:

basin of water, the water is found to move upwards through the soil See also:

COLUMN (Lat. columna)

column just as oil will rise in an ordinary See also:

LAMP (from Gr. Xag ras, a torch, Xaµaav, to shine)

lamp See also:

WICK

wick .

By this capillary action water may be transferred to the upper layers of the soil from a See also:

DEPTH

depth of several feet below the surface . In this manner plants whose roots descend but a little way in the ground are enabled to draw on deep supplies . Not only does water move upwards, but it is transferred by capillarity in all directions through the soil . The amount and See also:

SPEED, JOHN (1552–1629)

speed of movement of water by this means, and the distance to which it may be carried, depend largely upon the fineness of the particles composing the soil and the spaces left between each . The ascent of water is most rapid through coarse sands, but the height to which it will rise is comparatively small . In clays whose particles. are exceedingly minute the water travels very slowly but may ultimately reach a height of many feet above the level of the " water-table " below . While this capillary movement of water is of great importance in supplying the needs of plants it has its disadvantages, since water may be transferred to the surface of the soil, where it evaporates into the air and is lost to the land or the crop growing upon it . The loss in this manner was found to be in one instance over a See also:

pound of water per day per square foot of surface, the " water-table " being about 4 or 5 ft. below . One of the most effective means of conserving soil moisture is by " mulching," i.e. by covering the surface of the soil with some loosely compacted material such as See also:

STRAW

straw, See also:

LEAF (O. Eng. leaf, cf. Dutch loof, Ger. Laub, Swed. lof, &c.; possibly to be referred to the root seen in Gr. Ma-eta, to peel, strip)

leaf-refuse or See also:

STABLE

stable-manure . The space between the parts of such substances is too large to admit of capillary action; hence the water conveyed to the surface of the soil is prevented from passing upwards any further except by slow evaporation through the mulching layer . 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 and See also:

HARROW

harrow are therefore excellent tools for use in dry weather .

See also:

CONSTANT, BENJAMIN (1845-1902)

Constant hoeing or harrowing to maintain a natural soil mulch layer of 2 or 3 in. deep greatly conserves the soil water below . In certain districts where the rainfall is low a crop can only be obtained once every alternate year, the intervening See also:

SEASON (0. Fr. seson, seison, mod. saison, Lat. satio, sowing time, the spring, from serere, to sow; in Late Lat. the word is found with its present meaning, the spring being considered as particularly the season of the year)

season being devoted to tillage with.a view of getting the rain into the soil and retaining it there for the crop in the following year . Bacteria in the Soil.—See also:

RECENT

Recent See also:

SCIENCE (Lat. scientia, from scire; to learn, know)

science has made much progress in the investigation of the micro-organisms of the soil . Whereas the soil used to be looked upon solely as a dead, inert material containing certain chemical substances which serve as food constituents of the crops grown upon it, it is now known to be a place of habitation for myriads of minute living organisms upon whose activity much of its fertility depends . They are responsible for many important chemical processes which make the soil constituents more available and better adapted to the nutrition of crops . One cubic centimetre of soil taken within a foot or so from the surface contains from i z to 2 millions of bacteria of many different kinds, as well as large See also:

numbers of See also:

FUNGI (p1. of Lat. fungus, a mushroom)

fungi . In the lower depths of the soil the numbers decrease, few being met with at a depth of 5 or 6 ft . The efficiency of many substances, such as farm-yard manure, guanos, See also:

bone-See also:

MEAL

meal and all other organic materials, which are spread over or dug or ploughed into the land for the benefit of farm and garden crops, is See also:

BOUND, or BOUNDARY (from O. Fr. bonde, Med. Lat. bodena or butina, a frontier line)

bound up with the action of these minute living beings . Without their aid most manures would be useless for plant growth . Farm-yard manure, guanos and other fertilizers undergo decomposition in the soil and become broken down into compounds of See also:

SIMPLE

simple chemical composition better suited for absorption by the roots of crops, the changes involved being directly due to the activity of bacteria and fungi . 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)

top dressing to wheat or other plants is well known to farmers: It has long been known that when organic materials such as the dung and urine of animals, or even the bodies of animals and plants, are applied to the soil, the nitrogen within them becomes oxidized, and ultimately appears in the form of nitrate of lime, potash or some other See also:

BASE

base .

The nitrogen in decaying roots, in the dead stems and leaves of plants, and in humus generally is sooner or later changed into a nitrate, the See also:

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change being effected by bacteria . That the action of living organisms is the cause of the production of nitrates is supported by the fact that the change does not occur when the soil is heated nor when it is treated with See also:

DISINFECTANTS

disinfectants which destroy or check the growth and life of bacteria . The process resulting in the formation of nitrates in the soil is spoken of as nitrification . The steps in the breaking down of the highly complex nitrogenous proteid compounds contained in the humus of the soil, or applied to the latter by the See also:

FARMER, RICHARD (1735–1787)

farmer in the form of dung and organic refuse generally, are many and varied; most frequently the insoluble proteids are changed by various kinds of putrefactive bacteria into soluble proteids (peptones, &c.), these into simpler amido-bodies, and these again sooner or later into compounds of See also:

AMMONIA (NH3)

ammonia . The See also:

UREA, or CARBAMIDE, CO(NH2)2

urea in urine is also rapidly converted by the uro-bacteria into ammonium carbonate . The compounds of ammonia thus formed from the complex substances by many varied kinds of micro-organisms are ultimately oxidized into nitrates . The change takes place in two stages and is effected by two special groups of nitrifying bacteria, which are present in all soils . In the first See also:

STAGE (Fr. 6/age; from Lat. stare, to stand)

stage the ammonium compounds are oxidized to nitrites by the agency of very minute motile bacteria belonging to the genus Nitrosomonas . The further oxidation of the nitrite to a nitrate is effected by bacteria belonging to the genus Nitrobacter . Several conditions must be fulfilled before nitrification can occur . 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)

guano, See also:

fish-meal, sulphate of ammonia and other manures take place, and the constituents which they contain become available to the crops for whose benefit they have been applied to the land . Nitrates are very soluble in water and are therefore liable to be washed out of the soil by heavy rain . They are, however, very readily absorbed by growing plants, so that in summer, when nitrification is most active, the nitrates produced are usually made use of by crops before loss by drainage takes place . In winter, however, and in fallows loss takes place in the subsoil water . There is also another possible source of loss of nitrates through the activity of denitrifying bacteria . 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)

atmosphere . Many bacteria are known which are capable of denitrification, some of them being abundant in fresh dung and upon old straw .

They can, however, only carry on their work extensively under anaerobic conditions, as in water-logged soils or in those which are badly tilled, so that there is but little loss of nitrates through their agency . An important See also:

GROUP

group of soil organisms are now known which have the power of using the free nitrogen of the atmosphere for the formation of the complex nitrogenous compounds of which their bodies are largely composed . By their continued action the soil becomes enriched with nitrogenous material which eventually through the nitrification process becomes available to ordinary green crops . This power of " fixing nitrogen," as it is termed, is apparently not possessed by higher green plants . The bacterium, Clostridium pasteurianunz, common in most soils, is able to utilize free nitrogen under anaerobic conditions, and an organism known as Azotobacter chroococcum and some others closely allied to it, have similar See also:

POWERS, HIRAM (1805-1873)

powers which they can exercise under aerobic conditions . For the carrying on of their functions they all need to be supplied with carbohydrates or other carbon compounds which they obtain ordinarily from humus and plant residues in the soil, or possibly in some instances from carbohydrates manufactured by minute green See also:

ALGAE

algae with which they live in close See also:

union . Certain bacteria of the nitrogen-fixing class enter into association with the roots of green plants, the best-known examples being those which are met with in the nodules upon the roots of See also:

CLOVER

clover, peas, beans, See also:

SAINFOIN

sainfoin and other plants belonging to the leguminous See also:

order . That the fertility of land used for the growth of wheat is improved by growing upon it a crop of beans or clover has been long recognized by farmers . The knowledge of the cause, however, is due to modern investigations . When wheat, See also:

BARLEY (Hordeum sativum)

barley, turnips and similar plants are grown, the soil upon which they are cultivated becomes depleted of its nitrogen; yet after a crop of clover or other leguminous plants the soil is found to be richer in nitrogen than it was before the crop was grown . 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

host plants and ultimately stimulate theproduction of an excrescent nodule, in which they live . For a time after entry they multiply, obtaining the nitrogen necessary for their nutrition and growth from the free nitrogen of the air, the See also:

CARBOHYDRATE

carbohydrate required being supplied by the See also:

PEA (Pisum)

pea or clover plant in whose tissues they make a See also:

home . The nodules increase in size, and analysis shows that they are exceedingly See also:

rich in nitrogen up to the time of flowering of the host plant . During this period the bacteria multiply and most of them assume a peculiar thickened or branched form, in which state they are spoken of as bacteroids . Later the nitrogen-content of the nodule decreases, most of the organisms, which are largely composed of proteid material, becoming digested and transformed into soluble nitrogenous compounds which are conducted to the developing roots and seeds . After the decay of the roots some of the unchanged bacteria are left in the soil, where they remain ready to infect a new leguminous crop . The nitrogen-fixing nodule bacteria can be cultivated on artificial See also:

MEDIA

media, and many attempts have been made to utilize them for See also:

PRACTICAL

practical purposes . Pure cultures may be made and after dilution in water or other liquid can. be mixed with soil to be ultimately spread over the land which is to be infected . The method of using them most frequently adopted consists in applying them to the seeds of leguminous plants before See also:

SOWING (from "to sow," O. Eng. shwan, cf. Du. zaaijen, Ger. saen, &c.; the root is seen in Lat. severe, cf. "seed")

sowing, the See also:

SEED (from the root seen in Lat. serere, to sow)

seed being dipped for a time in a liquid containing the bacteria . 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