Introductory Soil Science PDF

I 2 Introductory Sot , science f o the soil, · and tfte other, b Y :__.ae. its classjfication aqd. its, descripVon~ h---...

I 2 Introductory Sot , science f o the soil, · and tfte other, b Y :__.ae. its classjfication aqd. its, descripVon~ h--- d hologist wh1c covers -. the ~tudy of soil in relation to growth, nutrition and yield of crops... that - -- - ---- --. - - -.. t view pomt is In this text book both branches are being discussed but the qomman of the edaphologist. Definition of Soil , ·.. k.s 1 Generally soil refers to the lose surface of the earth as 1dentt. "fi1ed f rom the ot1gmal roe and minerals from which_ it is derived through \Yeath~ring proce~ses. " Sotls. are apphed. solely to those supetfi~1al.. or nearly'-supe. rfi1c1a. 1 horizons ,.. of rocks,. that have been more or less m~dified, n1turally by the intdaction of water, a~r and vano~s kinds of organisms, either living or dead; this being reflected in a certam manner m composition, structure and colour of such formations. Where this conditions are absent, there are no natural soils, but either artificial mixtures or rocks." -Dokuchaev ~ oil is a natural body developed by natural forces acting on natural materials._ It is usually differentiated into horizons from mineral and organic constituents of vanable depth which differ from the parent materfal below in morphology, physical properties and constituents, chemical properties and composition and biological characteristics." · -Joffe and Marbut "Soil is the more or less loose and crumby part of the outer earth crust in which; by means of their roots, plants_may or do find foot hold and nourishment as well as all other conditions essential to their growth." -Hilgard Soil may be defined as "A dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms." · -Buckman and Brady So, in a generalised fonn soil may be defined as an accumulation of natural b d" which h has been synthesized in profile form from a diversified mixture of disint do ies d weat ere mmer s an ecaymg organic matter w 1c covers the surface of the earth and. al d d.. h" h egrate which supphes, when contatmng the optimum amounts of air and water, mechanic ' and and sustenance for plants. · a support 1 Components of Soil Soils consist of four major components viz., (i) mineral matter C-) ·. (iii) water and (iv).air-All these components cannot ·be s e p ~ ' t h ll 0 £gill:l!S:-mmter. beca~ey are present very intimately.mixed with each other. The 1. much sattsfaction the bulk of soil solids and a very small amount of the soil solids occ _mdineraI matter forms twi sby orgaruc Physically, the soil consists of ~tones, large pebbles, dead plantup1e. matter. other parts of the plants, fine sand, silt, clay and humus-derived f g ' roots, leaves a d organic matter. rom the d ecornposition nof In the organic matter portion of the soil, about ha1f of the total. · h ·11·, · II of the dead remams oft e soi 1ie m a stages of decomposition d organic n..0 atter corn. the organic matter in the soil is alive. · an the remaining hPnsed. alf of t Concept of Soil 3. The living Part _o f ~he organic matter copsists of plant roots, bacteria, earthworms, algae, fungi, nematodes, actinon,.y~etes and many other living organisms. Volume Composition of Soil '· The volume composition of soil in optimum condition for the crop growth are as follows : , , · ;. VOLUME COMPOSITION 45 PERCENT MINERAL OF SOIL t------ SOLID S P A C E I,-- - - MATTER (50 PER CENT) _ ___ 5 PER CENT ORGANIC MATTER ,__ _ _ 25 PER CENT WATER TOTAL SPACE 1------ (50 PORE SPACE PER CENT) , , , , (100 PER CENT) , - 25 PER CENT AIR. Soil contains about 50 per cent ·solid space and ·50 per cent·pore space. The total solid spa~e of the soil is occqpied l;>y mineral matter and organic matter by about 45 per cent and 1 1 \ I t i ' 5 per: cent respec~tvely. ,The tot~ pore spa:ce of the. soil is ,occupied by air and water on 50 : 50 basis, i.e. in tris ca;se ~5-per cent air a11d ~5 1.J,~r cent water. 'I)ie pr,oportion of-air and water will vary under natural conditions depen