SOIL RELATIONS ' 247 



omists themselves is either not extensive or not well de- 

 fined or harmonized. Field crop students have not 

 looked below sufficiently, but have made their studies 

 entirely above ground, as a rule, while the soil specialists 

 usually have not sufficiently connected their soil studies 

 with the crop as an index. An interesting fact brought 

 out in one's association with farmers, and in the general 

 literature of the country, is the prevailing emphasis 

 given to the food value of soils for certain crops. The 

 truth is that, in a given large area of country, the real 

 basis of comparative values in almost all cases is a ques- 

 tion of water supply. 



The ability of different soils to absorb and retain water 

 is dependent chiefly upon their mechanical structure, 

 though the presence of alkaline salts and possibly other 

 factors have influence. According to the soil classifica- 

 tion adopted by the United States Bureau of Soils, the 

 types of agricultural soils as to texture are as follows : 

 sand, fine sand, sandy loam, fine sandy loam, loam, silt 

 loam, clay loam, and clay. Water absorption and reten- 

 tion increase in proportion to the fineness of the soil. 



262. Sandy versus heavy soils. Of course any par- 

 ticular soil will have a mixture of several types and be 

 designated by the name of the preponderant type. In 

 common talk, soils are lumped into two general classes, 

 of light or sandy, and heavy or clayey soils. In the 

 southwestern plains the latter are usually called " tight 

 lands." As the heavy soils, composed of a larger per- 

 centage of finely divided particles, will absorb and retain 

 more water it might naturally be supposed that they 

 are the better soils. In actual farm practice there are 

 perhaps about as many advocates of sandy soils as of 

 heavy soils, so long as the former has not reached such a 



