172 SCIENTIFIC AGRICULTURE. 



mold, is superior in all respects to to one composed of either of 

 these ingredients alone. 



Firmness and adhesiveness. Most soils become hard and 

 stiff in some degree, by the cohesion of their particles after 

 being thoroughly wet. Clay soils become hard and difficult to 

 pulverize when thoroughly dried, while pure sand soils scarcely 

 cohere at all. This varies according to the relative amount of 

 sand and clay or lime in the soil. The practical inference is, 

 that a sandy soil is improved by clay, and a stiff clay soil is 

 ameliorated by sand. 



The power of imbibing moisture is possessed by all fertile 

 soils. In dry weather, this quality in soils is highly important, 

 in order that moisture may be absorbed from the dews of the 

 night, to compensate to the roots of plants what they had lost 

 by exhalations from their leaves and evaporation from the soil, 

 during the day. 



During a night of twelve hours, when the air is moist, 

 according to Schubler, 



1000 pounds of perfectly dry quartz sand will gain Ibs. 

 " " Calcareous " " 2 



" " Loamy soil " 21 



" " Pure agricultural clay " 27 



" " Rich peaty soils, still more. 



Power of containing water, in dry climates, constitutes one 

 of the most important characteristics of arable soils. A good 

 soil for ploughing or tilling must be capable of containing from 

 30 to 70 per cent, of its weight of water: soils which allow 

 their moisture to sink down immediately after rains, below the 

 reach of the roots of plants, are valuable only " for pine plan- 

 tations or laying down to grass." [Johnston.] 



The following table from Schubler shows the relative capacity 

 of soils for containing water. By this, we mean, the amount 

 of water which a given quantity of earth will imbibe and 



