SOBRALIA 



9. L6wii, Rolfe. Au imperfectly known species in- 

 troduced about 1892 from Colombia. It grows about 

 VA ft. high and has fls. of a bright uniform purple. 



The following trade names are not accomited for : S. mag- 

 nifica.—S. Pfaiiii.—a. virgindlts. 



Heinriuh Hasselbking. 



SOIL. The soil is a superficial covering of the earth's 

 crust, more or less well adapted to the growth of plants. 

 It is usually only a few inches thick. Below this i.s a 

 subsoil often ditTi-riiii.'. espii-ially in humid climates, 

 from the soil propi i- in .-"l.ir, trxturi-, nr i-liemical com- 

 position. A very siiikiii- .iiliiiiti..,, lias l..-i-n suggested 

 by Sir John B. L:i\v.s. hIi.. nmM.l.icd tlie soil to be 

 rotten subsoil, and lln.^ sutsuil rutting ruck. The term 

 soil is occasionally used in a more comprehensive way 

 to include both the soil and the subsoil. 



The soil adapted to the growth of the higher plants 

 consists of fragments of rocks or minerals, organic 

 matter, soil solution, and a soil atii...s|,li.n-. The 

 mineral fragments vary in size trcMii tlir liiiivt I'lay 

 particles to gravel and even bouldci-. I'hr ..ricanic 

 matter is derived from low organisms, fruiii pnvious 

 vegetation, or from growing plants; as also from stable 

 manure, and occasionally fish or animal matter added 

 to the soil by man. The soil solution consists of water 

 carrying dissolved substances derived from the soil 

 grains and from the organic matter, as well as from 

 fertilizing materials artificially applied, and constitutes 

 a nutrient solution from which the plant derives its 

 mineral constituents. The soil atmosphere differs from 

 the ordinary atmosphere above the soil in being richer 

 in carbon dioxid and nitrogen, and containing more 

 water vapor and less oxygen. 



In origin there are two main classes of soils: seden- 

 tary soils, formed by the disintegration and decomposi- 

 tion of rocks ill |.Ia.-,-: and Iraiisi.uii,.! s..ils, iiirlinling 



alluvial is Iktu iis<mI tu iii<-luiif all w al.i-lran~|N)i-ted 

 material; tlic ii-rm is, li..w.-vi'r, fri'.|u.-utly ummI in a 

 more specific sunsu tu indicate the recent tiuuii deposit 

 of rivers. 



Soils are classified according to their origin and their 

 mechanical and chemical composition and properties. 

 Genetically, they are classitii-d accurdiiii; to the rock 

 from which they are denvid, ,i- :;raiiit.- soil, lime- 

 stone; or according to tli. - ■ : ■ r . : i ,. ir origin, as 

 alluvial, lacnstriaii or .In!' M. ,!lv. they are 



classified broadly iiit,. si..i, _; -andy, sandy 



loam, loam, clay luani, rla\, a! . ■ I waw. "i. 

 according to some ..ili.r |ili\ si, -al |a-..i. ^ . ., . " 

 into calcareous. Ininius. alkah. an-i a -i : ■ ■ ■ r 



striking chemical f.aiuns. In ili. -■ ,i ,i , , ■ iii> 

 U. S. Department of AKrifuUure a lu.al nana i- au-ia. .1 

 for each type untler which tlie speciiia rliaiaii, is arr 

 given; examples of this are Hartford saiulv iMam. Xur 

 folk sand, San Joaquin adobe, CTlendali- jurss. 



The physical properties of soils cuiiia-ni tlii> si/,' ami 

 arrangement of the particles, and the relation ,'i iIh-si- 

 to each other and to the organic matter; als,. th, sml 

 atmosphere, the soil moisture, and the pliysi.al fur, as 



zation so that crops may annually remove larger quan- 

 tities of nutrient substances without any particular 

 exhaustion to the soil. 



It is certain that these nutrient materials do not ac- 

 cumulate to any considerable extent in soils in humid 

 countries, as they are liable to be leached away and also 

 to recombine, forming diflficultly soluble compounds 

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

 heart or good condition when the physical conditions, 

 such as the water supply, soil atmosphere and tempera- 

 ture relations, are favorable, and when the weathering 

 of the material is sufficient to furnish an abundant and 

 constant nutrient solution in the soil moisture. 



One of the most potent agents in the weathering of 

 soils is the organic material contained. This is unques- 

 tionably due largely to the amount of carbon dioxid 

 formed, which ren<lers many of the nutrient matters 

 much more soluble. Moreover, the organic matter forms 

 a culture medium for bacteria, ferments and the vari- 

 ous organized and unorganized agents which assist in 

 breaking down the organic material, and facilitate as 

 well the weathering of the other soil components. Soils 

 in general have remarkable power of absorbing on the 

 surface of the soil grains vast quantities of carbon 

 dioxid, ammonia and other gases, and of other nutrient 

 materials, which while soluble and actually dissolved, 

 do not readily diffuse out into the solution between the 

 soil grains. 



The influence of fertilizers is therefore twofold: the 

 direct addition of plant-food for the immediate use of 

 plants, and the action of the fertilizing components 

 upon the solubility of the otherwise difficultly soluble 

 compounds in the soil. There are other offices which 

 are very strikingly shown in the ca.se of lime. This 

 substance when in the form of either caustic or slaked 

 lime corrects the acidity which is very often present in 

 soils. It chan-is tin-' siructure of soils. It renders 

 some of the suil , ,.iii|.umiits much more soluble, espe- 

 cially when tin- liini- is ill the form of the sulfate or 

 gypsum, and it lias umluulifedly a physiological role 

 which enables the plant to assimilate larger quantities 

 of other nutrient matters even in amounts which would 

 be detrimental if the lime salt were not present in ex- 

 cess. 



The principal objects of the cultivation of the soil are 

 to secure proper aeration, to conserve the moisture sup- 

 ply, and to improve the drainage. The irrigation and 

 artificial drainage of soils are treated elsewhere. 



of heat 



In fin 



cultly 



s.iliitiuii .iissolyim; its material from tin 



lnl,l ipuuials in the soil and from fert 



ly appliiil. The amount of sulistama-s ir 

 ies with the moisture content and with th 

 'i is supplied to the soil. The ,liss,,l\,, 

 naturally present in the suil ui- ,1, riy, ,1 

 fertilizers, influence the solubility of tia- suil ,■ 

 nents, rendering them more or less suliilih- a,a-,ii,l 

 their nature and existing conditions, li is pi, 

 that there is a normal weathering uf tin- s,,il m; 

 which produces a certain concentratiun in th, s,>i 

 tion which will be maintained on the (gradual with, 



natural wi-ath.-rins,' is ,,fti-n la.t siitli,-i,-iit in .amu 



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



decay in piles. 



The larger pile is composed of sods. 



The physical prujierties of texture and structure, that 

 is, the sizu tiial arraiiL-, i:a lit uf the soil grains, have a 



i;rfafcr ]ira,(i i ,■ >■ with field crops and the 



lahitiun (,f , I, 1 , i,r extensive cultivation than 



iipun hurti, iilini ,1 , i,>|i~ .itlii-r in the field or green- 

 house, where uiti-nsiit- nuihuds are used. Particularly 

 in the eastern states, where the natural rainfall is re- 

 lied upon for the water supply, these physical proper- 

 ties have great influence in determining the relation of 

 crops to soils. This is due in large part to the influence 



