PHOSPHORUS FOR SOILS. 187 



Eiver are nearly all of them deficient in phosphorus, 

 if we buy it and use it on alfalfa meadows, then 

 feed the alfalfa hay and put back the manure, we 

 are steadily adding to our capital of fertility; not 

 much is lost, only we sell away in the bones of our 

 cattle, pigs and sheep a part of it and in their flesh 

 and blood a little more. An alfalfa farm may thus 

 become a great laboratory of fertility gathering, 

 provided the crops are fed on the farm. When they 

 are sold off the story is different. 



How Much Phospliorus? — In England it is the 

 custom to apply very large amounts of basic slag to 

 their meadows and pastures far in excess of what 

 the plants can take up, and they seem to get large 

 profit from so doing. There is lack of careful ex- 

 periment to show us what amounts of phosphorus 

 will pay best sown with or on alfalfa. The require- 

 ments of the plant, that is, the amounts actually 

 taken away from the soil, are as follows : 1,000 lbs. 

 of alfalfa hay contains 5 lbs. of phosphoric acid; 4 

 tons, or 8,000 lbs., would then contain 40 lbs. of 

 phosphoric acid. Two hundred and fifty pounds of 

 16% acid phosphate would contain that amount, 

 and should make good what was removed from the 

 soil by the 4 tons of hay. That there should be abund- 

 ance in supply the writer advises the use of 300 

 lbs. annually of 16% acid phosphate, or propor- 

 tional amounts of the stuff, if a different percent- 

 age is bought. Thus if only 10% of available phos- 

 phoric acid is present one would need to use 400 

 lbs. or more. So it is cheaper and better to use only 



