THE CAUSES OF LOW YIELDS 261 



seed on a healthy soil or by chemical or physical treat- 

 ment to destroy the bacteria or fungi present. 



212. Heavy Spring Frosts. In Western Canada most 

 of the grain crops must be sown before danger of spring 

 frosts is past. The only means of lessening the damage 

 from such late spring frosts as may come are, first, to 

 have seed of strong vitality in order that the young 

 plants may have the greatest possible chance to recover, 

 and secondly to have the soil in the best possible condi- 

 tion in order that the weakened plants may be well sup- 

 ported in their efforts to recover. 



Damage may be prevented to some extent by some- 

 what later seeding and by seeding the hardiest kinds 

 first and the tenderest last. But with grain crops 

 especially it is generally wise to risk the spring frosts 

 rather than to sow late and run the danger of fall frosts. 

 The latter do very great damage occasionally, but spring 

 frosts seldom do serious harm to cereals except when ac- 

 companied by a long period of dry weather or by soil 

 drifting. If the tender crown is exposed by blowing the 

 effect of spring frosts may be disastrous. 



In order of hardiness in spring the cereals rank as 

 follows : Rye, wheat, oats and barley. Flax is not less 

 tender than oats or barley, but if frosted, does not re- 

 cover so well on account of its habit of branching above 

 ground. It is therefore not usually sown until after 

 the cereals. Peas withstand spring frosts quite well but 

 if injured recovery is much slower and less complete than 

 with the grain crops. Corn and potatoes are very tender 

 but potatoes will recover from frosts that kill corn. 



213. Hail Storms. This is one of the factors affecting 

 crops that man has no power to control. The only way 

 in which he can play safe is by insuring his crop. It is 



