THE PRINCIPLES OF INTEBCULTUUE 



209 



available form is usually more limited than the water 

 supply, the consumption of plant food by weeds may be 

 even more injurious than the consumption of water. Only 

 when water and fertility are far in excess of the needs of the 

 crop could weeds do no harm. 



The effect of witch grass in reducing yield is illustrated 

 by data obtained at the New Hampshire station (Bulletin 

 71, page 55). Two plats of corn were treated in the same 

 manner and given good cultivation up to June 10. One 

 plat was hand-hoed four times after this date in order to 

 destroy the witch grass, while this was allowed to grow 

 in the other plat. 



TABLE XLIX 

 Effect of Witch Gbass in Corn 



We may conclude that, for corn, the principal object 

 of intertillage is to destroy weeds, and after this is accom- 

 plished, further tillage will not pay. 



The above does not apply to small tilled crops, as vege- 

 tables where the soil is exposed and the roots do not fully 

 occupy the surface soil. Here conditions approach those 

 obtaining on fallow soil. 



DEPTH AND FREQUENCY OF CULTIVATION 



145. Since intertillage in corn apparently serves no 

 important function beyond subduing weeds, it is to be 

 expected that no increase in yield will result from culti- 



