210 



ANNUAL R5:rORT OF THE 



Off. Doc. 



tbe plow slice? Yet if one field is underlain with a stiff, impervious 

 clay while another has a bed of sand it may make the most striking 

 difference in '-rop adaptation or yields. What the hand lens is to 

 the botanist, what the agar is to the bacteriologist, what the 

 chemical balance is to the chemist, the soil iiUiiw is to (he soil ex- 

 pert. Each helps to widen our field of knowledge. The man with 

 an auger who has taken the place of the men with the hoe in maga- 

 zine literature can pass rajiidly ovj^r thf' tiold and bring to view 

 a section of soil to the depth of three feet or even to six feet, if 

 necessary. He is thus able to explain almost instantly many differ- 

 ences in crop adaptation or yield that may have puzzled the farmer 

 for years. It is certainly somewhat remarkable how accurately 

 properly trained men can identify and map the different soil types. 

 I once described to a man who was personally acquainted with a 

 region the characteristics of that region. The soil was described, 

 the relative occurrence of different crops, the difficulties farmers had 

 in raising certain crops in that region, even the character of farm 

 imi>rovemeut was mentioned. When I was through with my de- 

 scription the man replied that it was exactly as he had observed it. 

 As a matter of fact I had not seen the region I was describing. 1 

 had simply looked at a soil map, knowing that certain conditions 

 existed elsewhere on this soil type, I described these observations. 

 The problem of the soil survey is to correlate and classify soils. 

 Th(i ni( thod of classification thus far worked out is first to estab- 

 lish different soil series in the different physiographic divisions of 

 the Uniied States. Each series is given a genus or surname as, for 

 example, Norfolk, Hagerstown, Dunkirk, or ]\Tiami. The Norfolk 

 series represents a group of soils of the coastal plain region, stretch- 

 ing along the Atlantic and Gulf States from Boston, 

 Massachusetts to Gralveston, Texas. The Hagerstown series in- 

 clude? the residual soils of limestone valleys occurring from 

 Pennsylvania to Tennessee. The Dunkirk series includes drift soils 

 redeposited by lake action occurring in the vicinity of the Great 

 Lakes, while the Miami series represents the upland types of drift 

 soil throughout the great Mississippi Valley. These soils are men- 

 tioned simply as striking examples of soil series. These soil series 

 are further divided into types based largely npon their physical pro- 

 perties and are designated by adding a specific or Christian name. 

 In order to understand fully the significance of the classification 

 into soil types, it is desirable to consider briefly the mechanical 

 analysis of soils. The soil particles are given names according to 

 their size (diameter in millimeters), as follows: 



1. Fine gravel, ... 



2. Coarse sand, .. 



3. Medium sand, . 



4. Fine sand, 



5. Very fine sand, 



6. Silt 



7. Clay 



mm. 

 2-1 1 

 1-.5 )• 

 .5-. 25 j 

 .25-.! 1 

 .1-.05 J 

 .05-. 005 

 .005-0 



Coarse sand 



Fine sand, . 



Silt 



Clay 



2-. 25 



.25-. 05 



.05-.0O5 

 .005-0 



These different sizes of soil particles occur in the different soils 

 in an endless variety of combinations and give to the soil in con- 

 nection with the organic matter, its chief physical properties and 

 to a gr'^at extent, at least, its crop adaptation. Based upon me- 



