28 COBN CROPS 



but the permanent roots develop at about the same dis- 

 tance below the surface. 



12. The spread of the roots. — Root studies on maize 

 at the Wisconsin, Minnesota, Colorado, New York, and 

 North Dakota experiment stations indicate that the 

 permanent roots first spread laterally for about nine to 

 twelve days, when they will have reached a distance. 16 

 to 18 inches from the plant and will be confined mostly 

 to a zone between 3 and 6 inches below the surface. From 

 this time on, the root system rapidly extends downward 

 as well as laterally, at eighteen days reaching a depth of 

 about 12 inches and at twenty-seven days a depth of 18 

 inches, with a lateral extension of 24 inches. By the time 

 the maize plants are two months old, when they are 5 to 

 6 feet high and coming in tassel, the lateral spread of roots 

 has a radius of about 4 feet and penetrates the soil to a 

 depth of 3 to 4 feet. The number of roots continues to 

 increase until the plant is mature, when they fully occupy 

 the upper 3 to 4 feet of soil. 



The depth to which roots may penetrate is somewhat 

 dependent on the character of the soil, as is shown by the 

 Colorado station. In a black adobe soil, the roots were 

 limited mostly to the upper 12 inches, while on another 

 heavy soil containing much clay they penetrated only 24 

 inches. 



13. Distance from surface. — At a distance of 6 inches 

 from the plant the upper roots are usually about 3 inches 

 below the surface, sloping gently to 4 or 5 inches deep at a 

 distance of 2 feet from the plant. However, when there is 

 abundance of moisture in the surface, feeders may come 

 within 2 inches or less. Distance from the surface seems 

 to be controlled by the presence of sufficient moisture, and 

 also by the degree of shading, since roots are very sensitive 



