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Show AGRONOMY i . Edited by Prof. J. C. Hogenson. A. C. U. SOIL FORMATION. Function. Soils arc the outer cov-cring cov-cring of the earth in which plants grow. They arc storehouse of moisture moist-ure and plant food and the medium in which plants place their roots so as to enable them to stand erect. Formation: Most soils arc complex com-plex material consisting of a mixture mix-ture of ground, rock, decayed plants and the remains of Insects and animals. ani-mals. Sands arc almost entirely particles par-ticles of rocks, while ipeat soil is almost entirely decayed plants. Geologists tell us that at first the surface has slowly been worked upon by a number of powerful agents until we have the soil formed as wc find it today. Among these agents wc may mention, (1) heat and cold, (2) water, frost, and ice, (3) vegetable life, (4) animal life, (5) air and wind. r Nearly all rocks arc made up of fragments or crystals of various stzts and shapes, these arc usually held together by some cementing material or else by direct cohesian when sufficient suffi-cient pressure has been exerted. Rocks arc never so closely grained, however, but that water can and is absorbed. In granite perhaps three pounds of water for one hundred pounds of stone. Heat and cold always al-ways work together. Nearly alt bodies expand or ibecome larger on being heated and contractor become smaller upon cooling. Jlhcse early rocks in the earth's formation were hot and as thcoutsidc crust cooled it contracted. This broke many of therpeks up into pieces and here and there left cracks. In these cracks water collected and froze and as freezing the water into ice causes great expansion this still further broke up the rocks. The s ,1ir, pieces were again acted upon in thST same way and arc still being acted upon. This action is still made SjjP-cr SjjP-cr when the rocks are made up or different kinds of crystals which do not all expand at the same rate This unequal expansion and contraction tends to loosen fragments and thus break the. rock down ond thus form 4 soil. A change of temperature of 150 J degrees F. will cause a granite rock J one hundred feet in diameter to expand ex-pand or contract one inch. Most people think of the soil merely mere-ly as dirt, as something unclean and undesirable. They think of it as a fixed thing unchangeable. That' the soil they walk upon today is the same as it was two hundred years ago, they have not noticed the slow but certain changes that arc going on about them. The mountains wearing away, and enriching the valleys, the filling j of. the swamps, whole mountain chains 1 have disappeared. The Appalachian Mountains have already lost, ly weathering and erosion as much as 1 now remains. Running water is a powerful soil former and soil destroyer. Notice a m t stream after a rain storm, its waters arc muddy. Soil is being carried from higher to lower levels. If you will ' notice even a clear stream as it ripples rip-ples over the uneven bottoms, little sand grains and gravel arc tumbled m and rolled along the bottom, at each U bend of the strcami soil is ibeing tak- F ... from the concave side and carried m onward to "the sea-while on the op- W. positc side 'new soil jisgjijg formed jj from that dragged along thc bottom, jt It is in this way the broatrjiver val- W leys arc formed. Most of the sod It carried by the rivers is deposited at y their mouths forming the deltas. It 1 is estimated that the Missippi carries 1 each year to the ocean enough soil to cover , one square mile 268 feet f deep. v ' j Ice has been al great factor in soil formation. At one time most of the upper part'of North Amcricawas cov-cred'lna cov-cred'lna vast sheet of ice. This was packcuf up in mountainlikc masses. .After a time some change in climate J Caused these mountains of ice to break i and begin to move south and west. M These great moving" masses carried W rocks and frozen capth along with W them and'1' ound them info powder. M exerting a pressure in some places ot jA two hundred thousand pounds per V square inch. "When the ice melted the ra great "mass of soil material hcy con- w taincd dropped. II v Ait, moisture n- l frost; conjointl; J I I I . formed another soil forming agent. r You may have noticed the outside of I certain rocks begin to crumble, this is called weathering and is due, largc- f ly to certain compounds in the air, acting upon the compounds of which the rocks arc composed, breaking them down, and also to the changing of temperature and the expanding and contracting . of the moisture. Upon this cumblcd rock mass low vegetable life first finds its home, the decay of these plants generation after generation gen-eration add fertility to the soil so that more highly developed or cx- tensive plants can grow there. The roots of plants in penetrating into the soil and crevices in the rocks help to split up the rocks. In due time animal life comes, to live upon the I plants, these animals iby their bur- ! rowing into the soil and allowing the air to enter and also by their constantly con-stantly mixing up the soil and sub-l sub-l soil and finally by their death aid still K more in bringing about our fertile soils. Swamp or marsh soils arc formed I almost entirely of vegetable matter V which has been slowly decaying un- f( dcr water, our lakes, ponds and swamps are being filled not 'alone by ,'J soil but also by plants whichthrivc n in water. a Tthc wind is 'both a soil builder and SyT tT soil rcjnjO.vcr especially when the n soils arc dry and loose. Valuable B soils arc sometimes totally destroyed' IT and covered by drifting sands. K& The soil is not dead ibut is teeming I ' with life. Countless tiny living or- f ganisms arc constantly at work i breaking down certain compounds, ancl building up others. Some arc bencfiicial, some arc hanmless and someja rh a r m f ul . lJt jg to yj&advantagcof the farmer ' therefore, to become sjfamiHar with Ir the various agencies at vxrk upon & his farm and turn them to his profit. Jr His soil is constantly changing, swept I by r wind worn and transported jby Sf1 water, refined by frost and air, loos- I ened and punched by plants and ani- r '(Continued on page 7) SOIL -CULTURE. (Continued from .pagcijV i- - A mals and worked upon by countless J bacteria. 2 Kinds. f There arc four general classes of j soils. 1st. Sand. Which is any rock r fragments ranging from .5 to .05mm mi diameter. .02 to .002 inch in diameter. dia-meter. It is distinguished from other soils by its large particles which arc non-cohesive. Each Grain is always separate from every other grain. It isof little agricultural value when purdVsand, but when mixed with a certain proportion of other soils becomes be-comes a valuable light agricultural soil. The xoarscr sands .are compos-ed compos-ed largely of quartz particles. 2nd . Guy. Soil particles less thaiv.005 --. mm in diameter .0002 inch, denotes a clay irrespective of the chemicak composition of the particles. It will hold a large per ccntagc of water and is usually cold and hard to work. If worked when too wet the texture is I oken down and puddling is the result. When clay soil dries it shrinks to a certain extent and so leaves the soil full of cracks. 3rd. Loarra of Silt. These names arc applied to soilshav-ing soilshav-ing soil particles whose sizes range between the sand and the clay. They usually contain considerable decayed vegetable matter and form our best agricultural soils as well as the most jfertile ones. 4. Humus soils arc soils that arc formed almost entirely of decaying organic matter in swamps, They arc usually light and loose, and ihave no body and no real agricultural valine va-line until mixed with a certain amount of mineral matter when they become rich and valuable soils. We may have and often do have mixtures of all three classes of soils, so that we have sandy loams, clay loams, etc. as a result. fj |