SOIL SANITATION 281 



This conclusion is borne out in actual farm 

 practice. The average farmer is familiar with 

 the curious phenomena of "sick" soils soils 

 that seem "sick" in so far as they refuse to 

 grow certain crops. Flax, it is generally as- 

 sumed, is wearing on soils subjected continu- 

 ously to its production. Those soils which tire 

 of growing flax are not deficient in the mineral 

 elements of fertility, as is easily proved by 

 planting them to other crops. The so-called 

 "clover-sick" soil is another instance. Almost 

 every farmer has seen within his own experi- 

 ence a plot of land that once grew clover well 

 suddenly become sterile as regards this plant. 



Reclaimed swamp soils seem particularly 

 susceptible to this so-called "sickness." In the 

 corn belt it is not unusual to see such soils 

 break down in the course of two or three years' 

 continuous cropping of corn, yet it is known 

 that their innate fertility measured in minerals 

 is high. In California reclaimed soils that 

 grew mammoth crops of potatoes at first 

 have frequently become unprofitable for 

 potato culture. Yet they respond admirably 

 to other crops. 



In the laboratory tests, the task of restor- 

 ing this sick soil to its original fertility as 



