50 THE SOIL OF TKE FARM. 



ute to the nourishment of crops. Deep jilowing is also 

 useful on thin lands where the upper layer is too clayey 

 and comi^act, and rests upon a hed of sand or limestone. 

 By plownig deep, the sand or Hme is mixed with the clay 

 above, rendering it more fertile than it could be made by 

 any other means. There are, however, cases m which, 

 from the defective composition of the subsoil, or other 

 causes, it does more harm than good. Good effects can 

 only be obtained from trench plowing when the chemical 

 composition of the lower soil is such as to supj^ly m in- 

 creased quantity the essential constituents of plant 

 growth. 



Where the subsoil is inferior, the deejDening of the soil 

 must be made a gradual operation, and a very small 

 quantity of the raw material brought to the surface at a 

 time. The sub-soiler effects this object much better than 

 the trench plow, as in the former case the subsoil is 

 opened up and exposed to the weathering action of the 

 atmosphere without bringing it abruptly to the surface. 



ORDINARY TILLAGE OPERATIONS. 



"Whatever the physical or chemical properties of the 

 soil may be, it will produce but little if not well tilled. 

 And what is true in this respect of the best soil, applies 

 in far stronger terms to the worst. 



Apart from its immediate end, the provision of a 

 proper seed-bed, the objects and effects of tillage may be 

 enumerated thus : — 



(1) To stir and loosen the entire soil to a sufficient 



depth : so that the roots of i)lunts may freely 

 extend themselves in search of food. 



(2) To pulverize the soil and mix thoroughly its 



constituent parts, so as to increase its absor- 

 bent and retentive powers, and to effect an 

 c<|ual and economical distribution of manure. 



