EXPERIMENT STATION BULLETINS. 



449 



crops produced. There are soils now practically sterile Avhich within 

 Ihe memory of the older inhabitants produced abundant yields of crops. 

 Assuredly this condition is not due wholly to the depletion of available 

 ])hosphorus, but that it is an important factor is evidenced by the bene- 

 iicial results received by many farmers who have made use of phosphatic 

 fertilizers. 



of phosphorus 



t~emove4 dnnual/y 



from /^ic/7iordn 

 Soils. 



of phosphorus 

 returnecl annua/Zy 



'3' 



Figure 13.- — If Michigan soils are to continue to be proiluctive or are to be increased in 

 productivity the use of the phosphorus must become general. 



The phosphorus situation on a given farm is governed largely by the 

 system of farming followed, the amount of feed purchased and the*^ care 

 of the manure produced. In the light of our present day knowledge the 

 conditions with respect to this element of plant-food on a dairy farm is 

 about as given in table 2. 



