300 THE SMALL GRAINS 



application of proper fertilizers (336), or, by a proper 

 system of rotation (342), to introduce crops having differ- 

 ent food requirements, or which may return to the soil 

 the very foods chiefly required by the preceding crop. 



326. Soil sanitation. Another possible injurious effect 

 of the crop upon itself, if grown several years in succession 

 on the same land, is the gradual accumulation of toxic 

 substances in the soil, resulting from the presence of im- 

 perfect fungi or other causes. These toxic substances 

 greatly reduce the yield (579). A kind of sanitation of the 

 soil in such a case is required which may be accomplished 

 by a complete reform in its treatment, involving thorough 

 cultivation using some intertilled crop and a good 

 crop rotation. 



