180 LECTURES ON 



shallow m the main, and our agricultural journals arc often occupied 

 with discussions as to the advantage or disadvantage of deep culture. 



There are. indeed, some instances in which deep ploughing is in- 

 jurious, either permanently, or as most generally happens for a short 

 period. In the latter case the temporary injury most often turns out' 

 to be a lasting benefit. 



Where a thin surface soil of fair quality rests upon a gravel or other 

 leachy stratum, too deep ploughing may, so to speak, knock the 

 bottom out of the soil, i. e., by breaking through into the open sub- 

 soil, may injure the retentive capacity of the upper soil for water and 

 manures. In case the sub-soil is of a "cold" ochery, noxious char- 

 acter, the bringing it to the surface may occasion detriment for the 

 time. 



The plough is the instrument most extensively employed for tillage, 

 and the one to which recourse must be had whenever large fields are 

 to be broken up. In ordinary ploughing the soil is inverted, and ac- 

 cording to its texture more or less pulverized and mellowed to a depth 

 of from three to six inches. Trench ploughing consists in a similar in- 

 versing of the soil to a considerably greater depth, as far as one foot or 

 more, and is practiced to advantage where the soil is good to this 

 depth, especially with the view of bringing up manures which are sup- 

 posed to descend and accumulate below. Sub-soil ploughing is intended 

 merely to break up and loosen the lower soil without bringing it to the 

 surface. The sub-soil plough is merely a narrow share or wedge that 

 follows the furrow of the common plough, and disturbs the ordinary 

 plough bed to the depth of several inches. Its employment is expen- 

 sive and less in vogue than it was a few years ago. It is mainly 

 useful where the sub-soil is with difficulty penetrable to water. 



In garden culture, or even in field culture in certain countries, as 

 in parts of Italy where labor is cheap, spading and forking are em- 

 ployed instead of ploughing, and with great advantages in heavy soils, 

 because the tread of beasts ol' draught is entirely avoided, and the 

 soil is much more throughly pulverized, intermixed and loosened up. 



After ploughing and if need be cross-ploughing, the harrow, 

 scarifier or cultivator, some form of toothed implement, is drawn over 

 the field to accomplish a sufficiently perfect comminution and levelling 

 of the surface for the seed-bed. On heavy clays which, especially 

 in vet weather, are thrown up by the plough in tenacious lumps that 

 further harden in the wind and sun, the clod crusher, a system of 

 toothed disks revolving at a little distance from each other on a com- 

 mon center, at right angles to the line of draught is employed. 



On very light soils the roller is used to make the earth more com- 

 pact, especially above the seed. 



In late years a countless number of modifications and not a few 

 improvements in the implements and methods of tillage have been 

 suggested, and to a greater or less degree employed, in practical agri- 

 culture; but it is not the place here to enter further into details. 



In certain localities, tillage may completely and profitably replace 

 all other means of improving the soil. 



It is obvious that with each harvest there is removed from the soil 



