TOTAL VS. AVAILABLE PLANT-FOOD ELEMENTS 357 



FIG. 225.' Not a fertilizer test only a difference in plowing To left, clover sod was 

 fall plowed as in Figure 75. To right, same kind of plowing but done in the spring. To 

 left, nitrification was retarded. (See Fig. 226.) 





FIG. 226. Proper cultivation overcame conditions shown in Figure 225. No difference 

 in yield at harvest time. 



