58 THE SOIL OF THE FARM. 



afford a reasonable amount of work for the tackle, it will 

 cultivate at a less cost per acre than the single engine tackle. 



Depth of Cultivation. — The proper depth at which to 

 cultivate must depend chiefly upon the nature and con- 

 dition of the soil, though partly also upon the kind of crop 

 to he grown. ^Vet lands should not be plowed deep 

 until they have been thoroughly drained. Alluvial soils 

 and deep clay loams, where the surface and subsoils do not 

 materially differ, can scarcely be tilled too deep. Thin 

 soils, however, should not for present profit be plowed 

 below the layer of mould; but their ultimate fertility 

 and capacity may be greatly increased by subsoiling and 

 heavy manuring for a series of years. It takes twice as 

 much manure to fertilize land Avhen it is plowed to a 

 depth of ten inches as when it is plowed five inches ; 

 and the converse is equally true — that by plowing only 

 five inches the soil will be exhausted much quicker than 

 when the plowing is ten inclies. But whether it in- 

 volves the necessity of additional manure or not, a tillage 

 depth of six to ten inches is vastly preferable to a less 

 depth. Von Thaer estimated that each inch of mould 

 between six and ten inches increased the value of the soil 

 eight per cent. 



The importance of deep tillage may be inferred from 

 the great depth to which the roots of some plants will 

 penetrate the soil, when conditions favor their doing so. 

 And a deep soil is as beneficial for the supply of moisture 

 during dry weather, as to give room for the roots of plants 

 to extend themselves. Further, the deeper stratum not 

 only renders the soil less subject to drouth, but it makes 

 it a better retainer of heat, and furnishes abetter medium 

 for the action of all the agents engaged in promoting the 

 vigorous growth of plants. 



Deep and thorough tillage, tlierefore, is to be extolled as 

 a general principle. Still, while it is useful to all crops, 



