74 



THE PRINCIPLES OF AGRICULTURE 



which is turned out of the furrow is a furrow-slice. In common 

 speech, however, the word furrow is often used for the furrow- 

 slice. 



91&. The accompanying pictures, adapted from Roberts' 

 "Fertility of the Land," illustrate different types of plow-work. 

 Fig. 19 shows the furrow-slice completely inverted, This kind of 

 plowing looks well, but it is not desirable unless the object is to 

 bury weeds or a green- crop. The furrow- slices are not broken. 



Fig. 23. A subsoil plow. 



Fig. 24. A smoothing harrow. 



and pulverized, and they are in such position that the harrow 

 cannot tear them to pieces. Fig. 20 represents work which is 

 better, for most conditions, although the slices are not pulverized. 

 Fig. 21 shows ideal plowing. 



91c. The ideal plow for general farm work, in Roberts' 

 opinion, is shown in Fig. 22. Observe the "quick" or sharp 

 curve of the moldboard. ' For an excellent sketch of the develop- 

 ment of the plow, consult Chapter ii. of Roberts' "Fertility of 

 the Land." 



93a. About 12 to 20 per cent of moisture in the soil is the 

 ideal condition for most plants. Let the pupil figure out what the 

 percentage will be after a rainfall of one inch on soils that are 

 four inches deep and eight inches deep. Consult Roberts, "Fer- 

 tility of the Land," pp. 77 to 79. 



94a. By hard-pan is meant very hard and more or less 

 impervious subsoil. Some subsoils are rbose ; others are so hard 

 as to prevent the downward movement of water and roots (79<z). 



