DEPTH OF CULTIVATION 77 



Experiments by Gates 3 and Cox, recently reported, verify in 

 general the above conclusions. 



Effect of Weeds. Weeds not only take up moisture but avail- 

 able plant-food as well. As the available plant-food in a soil is much 

 below the needs of the crop, all taken by weeds directly robs the crop. 

 Where weeds are allowed to grow the yield is almost nothing, while 

 simply scraping the weeds off, as indicated in above experiments, 

 results in yields comparable with thorough cultivation. The follow- 

 ing results for one year show effect of weeds : 



Reduced Yields Due to Weeds 



Weeds Weeds 



Place of experiment allowed scraped Shallow 



to grow off cultivation 

 New Hampshire Station (Bulletin 



71, 1900) 17 ... 80.0 



Illinois Station (Bulletin 31, 1894) none 28.7 36.1 



The function of interculture for corn then appears to be (1) 

 to conserve moisture and destroy weeds up to the time the plants pro- 

 tect the land, and after that (2) principally to destroy weeds. Broad, 

 flat shovels or shears that merely shave the surface are very effective 

 for killing weeds. 



The above principles apply to all cultivated crops. The more 

 nearly the field approaches a fallow field the more effective is cultiva- 

 tion for conserving moisture, while, on the other hand, the more 

 the condition approaches that prevailing in a wheat field, the 

 less need there is for conservation of moisture. For example, an 

 onion field is not only exposed but onion roots are very short, and 

 cultivation among onions is very important in conserving moisture. 

 The same is true of many vegetable crops. 



Depth of Cultivation. There is no real necessity of cultivating 

 deep if the work can be done while the weeds are small. Deep culti- 

 vation with wide shovels will often be necessary to cover up and 

 destroy large weeds. 



The depth of cultivation should be regulated so as not to destroy 

 corn roots (Fig. 29). In heavy soils and wet seasons roots are often 

 very shallow, from one to two inches below the surface ; in dry seasons 

 with loose porous soils, the upper roots will be three to four inches 



8 U. S. Bureau Plant Industry, Bulletin 257. 



