206 



NITROGEN, PHOSPHORUS AND POTASSIUA1 



No farmer, however successful, should ever think of trying to 

 maintain the fertility of his soil through the use of commercial 

 fertilizers alone. Legumes, grass, green manuring crops and barn- 



FIG. 137. Four rows without fertilizer in the drill. To the lett and right 125 pounds 

 of a 1-8-1 mixed fertilizer were applied per acre in the drill with a fertilizer attachment 

 on the planter. (See Fig. 138.) 



FIG. 138. An eighty-one per cent increase in silage corn at harvest time. To left, unfer- 

 tilized, 8.7 tons per acre; to right, fertilized, 15.8 tons per acre. A long-cropped soil. 



yard manure are indispensable. Except for truck crops and pota- 

 toes, it is wise economy to use commercial fertilizers in a definite 

 plan of more permanent soil improvement and fertility mainte- 

 nance rather than to make light applications mainly to stimulate 



