32 VERMONT AGRICULTURAL REPORT. 



the relation to its micro-org-anic life, are recognized today as im- 

 portant. 



I. Chemical Composition. 



Soils vary greatly as to chemical composition, and naturally 

 so. The product of disintegrated rock and decayed vegetable 

 matter, they partake of the nature of the materials from which 

 they are formed, mineralogically as well as chemically. Slate and 

 limestone, for instance, are highly unlike, and soils derived there- 

 from are similarly unlike. Then, too, the natural processes of 

 rock disintegration, the uneven weathering of rocks of varying 

 types, the mechanical and chemical action of water, eroding here, 

 dissolving there, have made gravel pits and sand banks, clay de- 

 posits and ox bows, have denuded the mountain slopes and en- 

 riched the valleys, have rearranged, sifted and sorted the various 

 materials once distributed with some uniformity, but now in 

 many cases concentrated. Moreover, throughout New England, 

 soils have been profoundly affected and modified by glacial action, 

 enriched here, impoverished there. Soils, then, are chemically 

 unlike because of their varied origins and processes of formation. 

 None of them contain the essential elements of plant food in the 

 proportions in which plants use them. A large part of the soil 

 performs no chemical function, but is simply a mechanical support 

 and anchorage, a theatre for biological activities, a reservoir for 

 water and for heat. It is the relative shortage of nitrogen, phos- 

 phoric acid, potash and lime in the soil, and their relatively large 

 usage by plants which gives them their prominence. It does not 

 follow, however, that soils containing equal amounts of these con- 

 stituents, even though all conditions are similar, would possess 

 equivalent crop producing powers. Their ultimate origin, 

 whether from rocks which were dense and hard, or from those 

 which were easily disintegrated, would be a factor in the case. 

 The one soil would yield up its plant food reluctantly, the other 

 readily ; yet chemical analysis would indicate essentially equivalent 

 crop producing powers.^ 



2. Physical Characteristics. 



Soils contain not only nitrogen, phosphoric acid and potash 

 in sundry combinations, but also air, water and heat. The proper 

 aeration of the soil, its adequate moisture content, its warmth, are 

 as essential to plant growth as is fertility, using the word in the 

 narrow sense. They contribute to its development in that they are 



'See in this connection Vt. Sta. Bui. 116, p. 183 (1905). 



