12 BULLETIN 143, U. S. DEPARTMENT OF AGEICULTUEE. 



Tables VI, VII, VIII, and IX show that in every case applications 

 of the slag fertilizer to the soils had a stimulating and beneficial 

 effect. 



The increase in growth caused by the citric soluble potash and 

 phosphoric acid in the slag was, as a rule, less than that caused by 

 the application of the equivalent quantities of these two fertilizer 

 elements in a water-soluble form, but this is to be expected in the case 

 of experiments carried on for such a short period of time. The tests, 

 of course, are not conclusive, but they indicate that good results may 

 be expected from the use of such a fertilizer. 



SUMMARY. 



A method of obtaining both potash and phosphoric acid in citric 

 soluble form has been devised. It consists of mixing together phos- 

 phate rock and feldspar with the addition of small quantities of the 

 oxides of iron and manganese to promote fluidity or lower the melt- 

 ing point of the slag, the mass being then heated to about 1,400° C. 

 for about 20 minutes. The resulting product is not only soluble in 

 a 2 per cent citric acid solution, but is also fairly soluble in water 

 saturated with carbon dioxide. Pot tests with typical soils showed 

 that the mineral increased the growth of wheat plants, but the bene- 

 ficial effect derived from such applications was not, on the whole, as 

 marked as it was when more soluble forms of phosphate and potash 

 were used. The indications are, however, that the slag product has 

 a distinct high fertilizer value. 



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