SUB-SOILIXG, TREJ^CH PLOWIXG, TILLAGE. 59 



it is of more direct imj)ortance to some j^lants than to 

 others. Root and green crops are the ones which benefit 

 most directly by deep cultivation of the soil. As these 

 crops usually follow grain crops, it thus becomes desirable 

 to give the deepest tillage on the grain stubbles. When 

 the land has been plowed or cultivated deej) in preparing 

 for the green crop, deep stirring for the subsequent crops 

 of the rotation may be not only unnecessary but often in- 

 jurious, as being unsuited to the habit of growth of the 

 plant under cultivation. 



Amount of tillage requisite. — Good husbandry gives 

 to every soil and crop its proper tilth. The stiffest and 

 poorest soils require the greatest amount of tillage. Light 

 soils, however, are rarely over-cultivated. As Tull, in his 

 philosophy of tillage, has pointed out, much plowing and 

 pulverizing of a naturally light soil will not make it more 

 loose and open, but have the contrary effect, making its 

 natural porousness less, and its density greater. 



It is possible, of course, to have a soil too loose, for it 

 must have a certain consistency to retain moisture and 

 support plants ; but too great looseness is a rare fault, and 

 one not without its remedy. By harrowing the land while 

 it is still damp, and by heavy rolling as it becomes drier, 

 the necessary degree of firmness may always be obtained. 



The soil is more frequently too open ; but that indicates 

 either a want of sufficient tillage or an injudicious apj)li- 

 cation of it. In dry weather clay soils are brought to the 

 finest tilth with the least labor, by harrowing immediately 

 after plowing or cultivating, and accompanying this op- 

 eration, when necessary, with the use of the roller. In a 

 similar season, lio-ht and drv soils must be sown and fin- 

 ished up as quickly as possible after plowing. In a wet 

 season, the best tilth is obtained by harrowing when the 

 soil IS in the stage *' twixt wet and dry." 



The mechanical condition of a good seed-bed should be 



