From the outer cortical myceliuni, again, branches pass through the epidermis and grow out in the soil, In stich cases the roots of the plants are usuall) found spreading in soils which contain a large amount of humus, or decaying vegetable matter.
The water content of the soil, its mineral content, its humus content, its temperature, and its physical characteristics, such as its depth and the size of its component particles are all edaphic factors.
Physically and physiologically dry habitats, with the accompanying plant communities of sand dunes and sandy heaths with little humus in the soil.
Mineral salts, especially calcium carbonate, often rich in acidic humous compounds, and characterized by oak and birch woods, siliceous pasture, and heaths with much acidic humus in the sandy soil.
Again, acidic humus does not form in calcareous soils; and hence one does not expect to find plants characteristic of acidic peat or humus on calcareous soils.
It is covered with a thick sheet of black earth, a kind of loess, that is mixed with humus.
Mosses and lichens are distinctive, as also are the birch, the dwarf willow and several shrubs; but where the soil is drier, and humus has been able to accumulate, a variety of herbaceous flowering plants, some of them familiar in W.
But it gave some impetus to the practice of green manuring with leguminous crops, which are equally capable with such a crop as mustard of enriching the soil in humus, whilst in addition they bring into the soil from the atmosphere a quantity of nitrogen available for the use of subsequent crops of any kind.
The result is a great destruction of the humus of the soil, and great leaching and washing, especially in the light loams of the hill country of the United States.
The exhaustion of the soil under cotton culture is chiefly due to the loss of humus, and nature soon puts this back in the excellent climate of the cotton-growing belt.
If the burningup of humus and the leaching of the soil could be prevented, there is no reason whyia cotton soil should not produce good crops continuously for an indefinite time.
This is especially true of the flood plains where the annual inundations prevent the formation of humus and retard forest growth.
It appears that with soils which are not rich in humus or not deficient in lime, calcium cyanamide is almost as good, nitrogen for nitrogen, as ammonium sulphate or sodium nitrate; but it is of doubtful value with peaty soils or soils containing little lime, nor is it usefully available as a top-dressing or for storing.
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.
Humus, the remaining constituent of soil, is the term used for the decaying vegetable and animal matter in the soil.
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 waterlogging, chalk enough to correct the tendency to acidity of the humus present, and would have within it various substances which would serve as food-materials to the crops.
025 or 03%, respond freely to applications of phosphates; probably in such cases even the weak acid is capable of dissolving out phosphates from the humus or other compounds which yield little or none to the roots of grasses and clovers.
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 change being effected by bacteria.
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 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 ammonia.
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 algae with which they live in close union.
Lime also assists in the decomposition of the organic matter or humus in the soil and promotes nitrification; hence it is of great value after green manuring or where the land contains much humus from the addition of bulky manures such as farm-yard dung.
This tendency to destroy organic matter makes the repeated application of lime a pernicious practice, especially on land which contains little humus to begin with.
The more or less dormant nitrogen and other constituents of the humus are made immediately available to the succeeding crop, but the capital of the soil is rapidly reduced, and unless the loss is replaced by the addition of more manures the land may become sterile.
When used on light dry land it tends to make the land drier, since it destroys the humus which so largely assists in keeping water in the soil.
The turf is taken off either with the breast plough - a paring tool pushed forward from the breast or thighs by the workman - or with specially constructed paring ploughs or shims. The depth of the sod removed should not be too thick or burning is difficult and too much humus is destroyed unnecessarily, nor should it be too thin or the roots of the herbage are not effectually destroyed.
It is best adapted for application to clays and fen lands and should not be practised on shallow light sands or gravelly soils, since the humus so necessary for the fertility of such areas is reduced too much and the soil rendered too porous and liable to suffer from drought.
On the light, poor sands of Saxony Herr Schultz, of Lupitz, made use of serradella, yellow lupins and vetches as green manures for enriching the land in humus and nitrogen, and found the addition of potash salts and phosphates very profitable for the subsequent growth of potatoes and wheat.
Rejecting the old notion that plants derive their nourishment from humus, he taught that they get carbon and nitrogen from the carbon dioxide and ammonia present in the atmosphere, these compounds being returned by them to the atmosphere by the processes of putrefaction and fermentation - which latter he regarded as essentially chemical in nature - while their potash, soda, lime, sulphur, phosphorus, &c., come from the soil.
Anelytropsis papillosus, of which only three specimens are known, from the humus of forests in the state of Vera Cruz.
The plain extending from Urfa to a dozen miles below Harran has a rich red-brown humus derived from the Nimrud Dagh east of Edessa.
Loamy soils contain a considerable quantity (30-45%) of clay, and smaller quantities of lime, humus and sand.
Vegetable soils or moulds, or humus soils, contain a considerable percentage (more than 5) of humus, and embrace both the rich productive garden moulds and those known as peaty soils.
Lime in the caustic state is beneficially applied to soils which contain an excess of inert vegetable matter, and hence may be used for the improvement of old garden soils saturated with humus, or of peaty soils not thoroughly reclaimed.
Hymenomycetes are a very large group containing over 11,000 species, most of which live in soil rich in humus or on fallen wood or stems, a few only being parasites.
Other species, especially the alligators, make a very large nest of leaves, twigs and humus, scraping together a mound about a yard high and two or more yards in diameter.
In the arctic zone they form to% of the flora; they will flourish in soils rich in humus which are too acid to support grasses.
Of Phanerogams, only the Dryas octopetala covers small areas of the debris, interspersed with isolated Cochlearia, &c., and, where a layer of thinner clay has been deposited in sheltered places, the surface is covered with saxifrages, &c.; and a carpet of mosses allows the arctic willow (Salix polaris) to develop. Where a thin sheet of humus, fertilized by lemmings, has accumulated, a few flowering plants appear, but even so their brilliant flowers spring direct from the soil, concealing the developed leaflets, while their horizontally spread roots grow out of proportion; only the Salix lanata rises to 7 or 8 in., sending out roots I in.
These soils are in general rich, but deficient in nitrogen and somewhat in humus; and in limited areas white alkaline salts are injuriously in excess.
In eastern Oregon the soils are of an entirely different type, being usually of a greyish appearance, lacking in humus, and composed of volcanic dust and alluvium from the uplands.