34 AGRONOM V 



through it readily. Sand contains very little plant food be- 

 cause this is so easily washed out by the rains. It is called a 

 light soil because it is so easily worked, though, bulk for 

 bulk, it is heavier than any other. The roots of plants pene- 

 trate sand without difficulty, but the readiness with which it 

 parts with its moisture renders it unsuitable for most crops. 

 Like clay, sand is of a variety of colors. Reds and yellows, due 

 to compounds of iron, are most abundant. 



Loam. A soil containing about equal parts of sand and 

 clay with some humus is called loam. If the sand is in excess, 

 it is called a sandy loam ; if the clay predominates, it is a 

 clay loam. Other constituents in the soil may modify it suf- 

 ficiently to entitle it to some other designation, as silt loam or 

 gravelly loam. Clay soils have from 80 to 100 per cent of clay ; 

 clay loams, from 60 to 80 per cent. Sandy soils have from 

 80 to 100 per cent of sand ; sandy loams, from 60 to 80 per 

 cent. The national Department of Agriculture is at present 

 analyzing and mapping the soils of the United States. As 

 fast as mapped, each type of soil is given a name to distin- 

 guish it. This is usually derived from some town located 

 upon the soil indicated, as Hammond silt loam, Hagerstown 

 loam, and Miami sand. 



Alkali soils. In various parts of the West the soils contain 

 an excess of the salts of sodium, magnesium, calcium, and potas- 

 sium, in which the ordinary cultivated plants will not grow. 

 Such soils are known as alkali soils. They usually occur 

 in regions deficient in rainfall, and the deposits are due to the 

 fact that the water from the scanty rains soon evaporates, leav- 

 ing on the surface the salts it has dissolved out of the soil. 

 Among these salts may be such familiar substances as common 

 table salt, Glauber and Epsom salts, and sal soda. Many 

 wild plants are not very sensitive to these salts and may 

 even thrive in such soils, but before the crops of the farmer 

 will grow, the alkali must be removed. In many soils this is 



