PRINCIPLES OF PLANTING AND CULTIVATION 31 



The heavy frame was supposed to act as a clod crusher, and the 

 teeth were not only to loosen but to stir the soil. This heavy im- 

 plement, together with the tramping of the animals, had a tendency 

 to leave the soil somewhat compact. It is only within recent years, 

 however, that the importance of thoroughly compacting the lower 

 strata of the seed bed has been appreciated ; but since extensive 

 investigations in soil physics have been carried on, and the move- 

 ment of water in the soil is more fully understood, the importance 

 of this feature in cultivation has been emphasized and is pretty gen- 

 erally understood by cultivators at the present time. The compacting 

 of the soil in the seed bed may be effected by an ordinary land roller 

 or, better still, by a subsurface packing implement, one of the best of 

 which is shown in figure 7 and is constructed as follows : A series of 

 ten or twelve independent cast-iron wheels about 2\ feet in diameter 

 are provided with a rim about I \ inches wide, and along this rim are 

 placed offsets about I \ inches wide and 3 inches long. These are not 

 placed opposite one another but are arranged alternately at intervals 

 of about 2 inches along the rim of the wheel. This gives the cast- 

 ing a surface nearly 6 inches wide, of which only about one half is 

 actually occupied by iron. When these wheels, which are upon a 

 common axle, are made to pass over the soil, the implement, having 

 sufficient weight to crush the clods, leaves the surface of the soil 

 comparatively loose and slightly rough, but the underlying portions 

 of the seed bed are forced compactly together. By following this 

 implement with a spike-tooth harrow which will cut 2 \ to 3 inches 

 deep, an almost perfect seed bed can be obtained. The subsurface 

 packing closes up the capillary tubes in the soil ; that is, it forces 

 the particles of the soil close enough together so that a compara- 

 tively small amount of water is sufficient to cause an upward move- 

 ment in the soil beneath. This compacting brings that portion of 

 the soil which has been displaced by plowing and harrowing into 

 intimate relation with the very compact substrata which have not 

 been disturbed by cultivation, and sets up a movement of water from 

 a considerable depth ; this is carried toward the surface until it 

 comes in contact with the loose blanket of soil which has been pro- 

 duced by the spike-tooth or acme harrow, leaving a loose mulch 

 2 or 3 inches deep over the surface. This is the ideal way of 

 preparing a seed bed for general farm crops. For truck crops, 



