'Vhv follinviiit: tr;i 

 iltra. — .S. I'tafni.- 



<!' 



soil tu he 

 TliL- term 

 nsive w;l\- 



SOBRALIA 



9. L6wii, Knife. An imperfeetly known species in- 

 tr<Mlu.'ea aliout 18'J'J from (.'oiumbiu. It .L^rows abi>nt 

 1 'o ft. high ami has fls. of a hrii;hc uniform purple. 



im^s -AVi' ncit a^'ruuiit-.'(l lor: ^ 

 ynu/lls. 



IIeinkkii Hassi-:lbkini;. 



SOIL. The soil is a .supcrflcial covcrin.Lr of the earth's 

 erust, more or less wt- 11 adapted to the yruwth of plants. 

 It is usually only a frw inches thiek. Below this is a 

 subsoil often differing:, espue tally in liumid olimati-s, 

 from the soil pru|Mr in color, trxturr. or rlM-mirid r<mi- 

 positiou. A vi-ry smkin:; ilL'tiiiitmu has hi 

 hy Sir John H. Lawrs. win. lMn"^ldl'^^d t 

 r.jtten subsoil, and the sul;soil rutriiii;' !••><■ 

 Si.ul is oeeasioually used in a nmri- fcuiiir 

 to iuclude l">oth the s^dl and tho suhsuil. 



The soil adapted to tht- Lcrowth <>( tlir lii-iier plants 

 consists of fratrments of rocks or minerals, organic 

 matti^r. soil solution, and a soil atm-'sphore. The 

 mineral fragments vary in size from the iinest clay 

 particles to gravel and even bouhh-rs. Tim organic 

 matter is derived from li>w organisms, frcnii previous 

 vegetation, or from growing' plants; a-; aN.. frnm stable 

 manure, and oeeasioually lish or animal nuirter added 

 to the soil by man. The soil SidutiMU C"n->i-.ts r*f water 

 carrying dissolved substances derived from the soil 

 strains and from the organic matter, a'-; wi.'ll as from 

 fertilizing materials artiticially applie<l. and constitutes 

 a nutrient solution from which the plant derives its 

 mineral constituents. The S(.)il atmosphere ditfers from 

 the ordinary atnu'sphere al'i.>ve the sidl in being richer 

 in carbon dioxid and nitn.tgeu. an<l containing more 

 water vapi.'r and le--s cix>"gen. 



lu origin there are two main chissi-s of si.ils: seden- 

 tary soils, forme<l by the disintegrath'U and decomposi- 

 tion (>t rocks in {ilace: and transported snils, incdndiug 

 tlio-^e of alluvial, glacial and aeotjan Mri-'in. The word 

 alluvial is here used to inchnle all water-trans]iorted 

 material ; the term i-.. 1m ^wever. frei(\iently used in a 

 more speciftc sense to indicate the recent tlond deposit 

 of rivers. 



Soils are classified according to tlieir orJLrin and their 

 mechanical and chemical c.impM.^ition aiirl ]iroperTies. 

 Genetically, they are classified nccoi-dim;- to the rock 

 from which they are derived, as granite soil, lime- 

 stone; or according to tin- nnaini 

 alluvial, lacustrian lU- drift. 31i 

 classitied broadly info stony, ur 

 loam, loam, clay loam, tdaw ad 

 aecordim: to ~nnie otlo-r i^hy^ical i 

 into calcare'.ms, Innnus, alkali, an 

 striking chemical feature--. In t| 

 U. S. Department of Agrii'ulture a 

 for each type under wdiich tin- s[ 

 given; examples of this are Hart] 

 folk sand, San .Joa^juin ad-be. (Tiendale U.-'-^-. 



The physical properties of smUs runcei-u the size and 

 arrangement of the partich-'s. and the relation of tiie^e 

 to eacli other and to the m-ganic matter; also the soil 

 atnnosphere, the soil moi--tnre. and the jilivsical forces 

 of heat antl gravitation. In these there is an intimate 

 relation with ]d^ysiography or the fMrni and e\p<isnre of 

 the siirfaci- of the land, as well as to climatoioi,^-. 



Then- are undMubte.Uy c-nsttuit physical chan-es 

 going on in the soil, as well lis chemical changes, which 

 have much to do with the lie-^t development "t vegeta- 

 tion. The soil moisture may be looke(l upon as a 

 nutrient solution dissolving its material from the ilitll- 

 cultly soluble compounds in the soil uwd from fertilizers 

 artificially applied. The amount of suhstaic'es jn solu- 

 tion varies with the moisture content and with the way 

 raoistui'e is supplied to the soil. The dis~(i|\-ed sub- 

 stances, naturally ]>reseut in the soil or derived from 

 fertilizers, influence the solubility of thi- soil coni])o- 

 nents, rendering them more or less soluble according: to 

 their nature and existing conditions. It is prohal)le 

 that there is a normal weatherinjg of the soil material 

 which produces a certain concentration in the soi) solu- 

 tion which will be maintained on the gradual witlnlrawal 

 of nutrient material by the plant. However, this 

 natural weathering is often not sutJicient in an)0unt to 

 produce the yield and quality i.f crops desired, and this 

 mav be increased bv methods of eu[tivati<ta and fertili- 



SOIL 



1G75 



zation so that cro]ts nuiy annually remove larger ipuui- 

 tities of mitrienl sulistances without any jiarticular 

 exhaustion to the soil. 



It is certain that these nutrient ]naterials do not a<.'- 

 (nimulate to any c'onsiderahle extent In soils in humhl 

 countries, as tliey are lialde to he leaciied awa\- and also 

 to recomldue, forming dilhcultly s<duble compounds 

 with the material of the soil grains. A soil is in good 

 heart or good condition when the physical conditions, 

 such as tlie water sup|il>", soil atmosj'here and reniijei-a- 

 ture relati<ins, are favorai)le, and when the weatliering 

 of the nuiterial is sullicient to furnish an abundant and 

 constant nutrient si.dution in the soil mcdsturc. 



One of the most ]M.teut agents in the weathering of 

 soils is the (.ir^anic ]naterial contained. This is um|Ues- 

 tionaldy due largely to the amount of •■arbon dioxid 

 formed, which renders many of the nutrieid nnitter-s 

 much more soluble. Moreover, the organic jnatter forms 

 a culture medium for bai-teria. ferments and the vari- 

 ous organized an<l unorganized agents which assist in 

 breaking ilown the organic nuiterial, an<l facilitate as 

 well the wi-athering (d' tin- other soil comp(.rients. Soils 

 in general haxe remarkalde i>ower cd' absorlnngon the 

 surface of the soil grains vast quantities of c;irbon 

 dioxid. annu'iida and other g.-ises, and of other nutrient 

 materials, winch while sohibh- and actually dissolved, 

 do not readil}- diffuse out into the solution between the 

 soil grains. 



The influence of fertilizers is therefore twofohl: the 

 direct addition of plauT-food for the immediate use of 

 plants, and the aidion of the fertili/.ing components 

 u[ion the solubility of the otherwise difliculrly soluble 

 ci.nnpi.iunds in the soil. There are other ot^ces which 

 are very strikingdy shown in the case of lime. This 

 substance when in the form of either causti'' or slaked 

 lime correids tin- acidity wliich is ver}' often ju'esent in 

 soils. It changes the structure of soils. It renders 

 some of the soil comi)oneuts much more solulde. espe- 

 cially when the lime is in the form of the sulfate or 

 gypsum, and it has nndouhtedly a ]ihysiologii;al role 

 which enables the plant to assimilate larger quantitii-s 

 'if otln-r nutrient matters even in aimamts which \\"'.mld 

 be iletriun.'Utal if the lime salt were not present in ex- 

 cess. 



The princijial oliject^^ ot the cultivation of the soil are 

 to secure in-oi»er a>Tatiim, to conserve the moisfuri- sup- 

 ph', ami t<> inipro\-e tlie drainage. The irrigation and 

 artificial draimige of soils are U-eated els^.\vhere. 



2333. How the gardener makes his soil, by letting- it 



decay in piles. 



The larger pile is coini>osed ot ^^ods. 



The 



■ater 

 atio 



iihysical proj.erties <.f texture am.l structure, that 

 size and arrangement <d' the soil grains, have a 

 er practical importance with field crops and the 

 d' crops to soil under extensiv*' cultivation than 

 upon horticultural crops either in the tield (U- green- 

 house, where intensive methods are used. Particularly 

 in the eastern states, where t)ie natural rainfall is re- 

 ipon for the wat^n■ su)iply. these physical ]irop'-r- 

 lave great influence in determining the relation of 

 . to soils. This is due in large part to the intiuem-e 



lied 



