48 VEGETABLE FORCING 



it contains. Classification is based upon mechanical 

 analyses, excluding stones, gravel and fragments of rocks 

 which do not pass through a 2-millimeter sieve. 



Classification of soil material 



The figures in the following classification,* represent 

 per cent; the minus sign ( ) less; plus sign (+) more; 

 the hyphen (-) when used between two numbers, as 20-50, 

 should read from 20 per cent to 50 per cent. 



Soils containing 20 silt and clay : 



Coarse sand: 25-}- fine gravel and coarse sand and less than 



50 any other grade. 

 Sand: 25+ fine gravel, coarse and medium sand, and less 



than 50 fine sand. 

 Fine sand : 50+ fine sand, or 25 fine gravel, coarse and 



medium sand. 



Very fine sand : 50+ very fine sand. 

 Soils containing 20-50 silt and clay : 



Sandy loam : 25+ fine gravel, coarse and medium sand. 



Fine sandy loam: 50+ sand, or 25 fine gravel, coarse and 



medium sand. 

 Sandy clay: 20 silt. 

 Soils containing 50+ silt and clay: 

 Loam : 20 clay, 50 silt. 

 Silt loam : 20 clay, 50+ silt. 

 Clay loam : 20-30 clay, 50 silt. 

 Silty clay loam : 20-30 clay, 50+ silt. 

 Clay: 30+ clay. 



It is seen from the foregoing classification that soils 

 vary greatly in the proportion of the different-sized 

 mineral particles. In the coarse sand the particles are the 

 largest ; in the clay they are the smallest. 



The proper soil texture is an exceedingly important 

 matter with reference to the production of crops under 

 glass. The heavier types, such as the loams, silt loams 

 and clay loams, are universally regarded as pre-eminently 

 adapted to the culture of the staple farm crops. Like- 

 wise, the value of the sandy types has been recognized for 

 trucking and market gardening, although many classes of 



* Bulletin 78, Bureau of Soils, United States Department of Agriculture. 



