109- 



. Color of soil. Cause, effect. 



Pure quartz, limestones, and similar soils ft re almost color- 

 less; white sands are good examples. A great variety of colors are, how- 

 evor, exhibited by most soils. These colorss are not usually the result 

 of the color of trie individual particles -which make up the bulk of the 

 material, but is rather the result of material which adheres to the par- 

 ticles. 



Color in soil is due to Uvo lu^in causes: iron compounds, and 

 organic nn.tl-:r. Iron ccMpoands produce reel, yellow, blue and gray col- 

 ors; organic mi r, an humus, produces a u- rk color, often acme shaae 

 of blnclc or brov/n. *$ien these are coi-i'oiiifcu, various intermediate tints 

 arc cbt , or ex^uple, ?;hen a rod soil is rich in decayed organic 

 r--] ~ .: e comes of r-, rich brown color. 



/ of organic matter will change a gay clay to a black 

 "waxy" l^.n; ; 11 amount will give a strong color. J&rown soils are 

 common over the 1 u L portion of the United States, ited soils are found 

 in the Jouth from Me--- "n^land to Texas, and also in arid countries and 

 in the tropic 3. Gr^y soilo are found in s e xndy lands, especially in the 

 far North-west, in regions of ^reot rnin. 



The color of soils, especially ae regards iron compounds, is not 

 fully understood, but it is safe to say that much color is the result 

 of different forms of iron in the soil. In the boulder clay of the gla- 

 ciateci nectiv-c;:.j a bluish color ia common, which seerr.s to i- due to the 

 presence of ;rotoxid of iron (I^eO), resulting from the ^r^at deficiency 

 n. ,re this cornes in contact with carbonated water, it may be 

 ch^n.rod to the car"= onnte of iron, which is gray, and consequently along 

 the .r.o,.Q t& line of roots and in the Dot torn of ponds this gray color may 

 bs f o . rid . 



Ihere there is an abundant supply of oxygen, the iron takes on 

 the seoquio, id (Fe^O^) form, which haa a deep red color, typified by 

 iron rust. Wuere the red soil stands much in contact with water, it may 

 become yellov by the hydration of the iron (Pe^G-j plus H^O). In many 

 regions a dark- colored soil is looked upon as a fertile soil. This rela- 

 tion has developed because of the association of a dark color with the 

 presence of organic .matter, with i,&fe all its beneficial effects, while 

 the lirjht color iridicp.tes its absence. This relation doew not nold uni- 

 versally, but it ia iuite a reliable guide. 



The only instances where the color of the particles themselves 

 give color to the uoil is in some of the clean quartz sands mentioned 



ve, Ther-i the white color of the dominant mineral gives color to the 

 maer>. In son.e dark elialey sands this same principle obtains. 



Soils may be classified by their color; color of soils is con- 

 nected with their temperature and physical condition; ihe&c two points 

 are useful in the field. To the experienced person, the color of the 

 soil is a valuable guide to its condition and productiveness. Bottled 

 anci uneven color, for instance, indicates poor aeration, frequently the 

 rerult of deficient drainage. 



