66 BREEDING CROP PLANTS 



The grouping of varieties and strains so that those of similar 

 habits of growth appear side by side removes to a considerable 

 degree the evil effects of competition. The most effective means 

 of overcoming competition is by the use of sufficiently wide 

 borders which are discarded at harvest. 



10. Results of field tests vary from year to year because of 

 changing weather conditions, and for this reason it is necessary 

 to extend a test over a period of several years. For varietal trials 

 a minimum of three years is recommended. 



