SUB-SOILING, TRENCH PLOWING, TILLAGE. 55 



in spring, and break up the weathered pan upon the 

 surface. 



The usual direction of harrowing after seed is sown is 

 first along the furrows, then across, and finally along 

 again. The quantity of land harrowed in a day depends 

 in a measure on the kind of harrowing as well as on the 

 kind of harrow used, and on the nature of the soil. A 

 two-horse set of ordinary harrows covers, usually, a width 

 of seven and a-half feet. That is equal to ten nine-inch 

 furrows with the plow ; so that if the teams trayelled at 

 the same pace, a pair of horses ought to harrow as much 

 land in one day as they could plow in ten. But horses, 

 as a rule, travel a good deal faster, and consequently 

 farther when harrowing than when plowing. It follows, 

 therefore, that if a plow, travelling at the rate of eleven 

 miles a day, with a nine-incli furrow, turns over exactly 

 one acre of land, a set of harrows, covering ten times the 

 width of a nine-incli furrow, and travelling one-fourth to 

 one-third faster than the plow, must get over twelve or 

 thirteen acres a day : that is, when giving one turn of the 

 harrow, or a single tine, as it is called. With a double 

 turn, only half that quantity of land would be covered in 

 a day. These are average quantities on average land. 



Rollin.!^ (1) breaks those clods or lumps which have 

 resisted the action of the harrow ; (2) it presses down 

 surface stones, etc., so as to be out of the way of the 

 scythe or reaping machine ; (3) it gives a greater degree 

 of compactness to soil which is too light and friable, 

 making it firmer around the roots of plants, and at the 

 same time a less favorable breeding-ground for many 

 kinds of insects ; while the smoother surface presents 

 fewer points of .evaporation ; (4) it presses down and 

 makes firm the ground about newly-soon seeds ; and some- 

 times (5), when very small seeds are to be sown, it is well 

 to roll the ground first, so as to level it thoroughly and 



