24 SOILS 



uneven and jagged, packing together tightly, like 

 the crushed rock of a macadamized road. 



The spaces between the soil particles differ in 

 size and shape, according to the size and shape of 

 the grains. I have met a farmer who could not 

 quite see how a soil could contain air at a depth 

 of four feet, yet he admitted that there must be 

 air at the bottom of his wheat bin. The trouble 

 was he looked upon the soil as a solid mass, since 

 he could not see the spaces between the grains 

 with his naked eye as he could in wheat. 

 If he would think of his soil as a bin of wheat, 

 with the kernels about one-millionth as large, 

 he could see how it is that air and water pass freely 

 through all ordinary soils, and to a great depth. 



It is of practical as well as of scientific interest 

 to know about the size of the grains of a soil, and 

 the size of the spaces between them. The value 

 of a soil for certain crops depends quite largely 

 upon just such factors. With the refinement of 

 soil surveys and methods, soil experts assure us 

 that they will be able to tell us with a fair degree of 

 certainty that soils containing, for example, from 

 250,000,000,000 to 350,000,000,000 particles per 

 ounce are adapted for potatoes; soils containing 

 350,000,000,000 to 450,000,000,000, for onions, 

 and so on. At present we classify soils and judge 

 their adaptability for certain crops in grosser terms ; 

 we say potatoes do best on a sandy loam, and that 

 an alluvial clay loam is excellent for onions. There 

 are limits to the practical value of this informa- 

 tion, for the fineness of the soil is but one of many 

 factors that determine the adaptibility of a cer- 

 tain soil for a certain crop; yet this one point is 

 extremely valuable to know when selecting land 

 for special crop farming. 



