78 JoiTENAL OF THE DEPARTMENT OJF AgHICULTURE. J ULY, 1922. 



fanners were always iirg-ed to purchase only liigh soluble slag-, and 

 the grades sold by the best firms Lad a solubility of 80 per cent, and 

 upwards. During- the war the process of manufacture changed, and 

 it is an open secret that the experts are no longer so much in agree- 

 ment as they were in regard to the desirabiltiy of a high soluble 

 slag. Experiments have been initiated to obtain more definite infor- 

 mation, and until these are completed it is not possible to lay down 

 precise rules for the farniers' gui(hince. In the meantime it is wise 

 to assume that a high soluble slag will usually come into action more 

 quickly than one of low solubility, and that a larger return ma> 

 therefore be expected in the first season. It is possible, however, 

 that in later seasons the low soluble slag may grow in effectiveness, 

 and at the expiration of five years there may be little difference 

 l)etween the two ; in some experiments, e.g. in Essex, this is clearly 

 demonstrated. Until more definite evidence is forthcoming perhaps 

 the safest assumption the farmer can make is that high-soluble slag 

 may pay him interest on his outlay almost from the beginning, 

 while the returns from low-soluble slag may be deferred." 



By high-solubility and low-solubility in this quotation, it may 

 be explained, is meant the proportion of citric-soluble to total 

 phosphoiic (jxide in a slag, and not necessarily the high or low ])ro- 

 portion of soluble phosphoric oxide to llie slag as a whole. 



In the Essex experiments (•())iij)tivative tests were made of the 

 foUoAving two fertilizers: — 



Pruliui-tidii of Citric- Soluble 

 ( 'lass of Fertilizer. in Total 



Phosphoric Oxide. 



< )pen-lieurth basic slag 'JO ])er cent. 



High-grade basic slag 01 per cent. 



The produce of two types of soil sowji with clover resulted as 

 follows : — 



Clover ... 

 Grass 

 Weeds . . . 

 Bare 



Dr. Russell's comment on this was that " the crop returns show 

 that high-grade slag is, as a matter of fact, rather better than low- 

 grade, especially in improving the quality of the herbage. The 

 diSerence is not so great as would be expected from the difference in 

 solubility, and it seems clear that present-day analvtical methods do 

 not deal satisfactorily with present-day slags." 



Such then is the position to-day. We have not yet come to the 

 stage of finality in the matter. It is tiue that general buying condi- 

 tions on the basis of 16.1 per cent, citric-soluble phosphoric oxide 

 cannot now be reached, but then we do not ask for such a basis, even 

 in our existing unrelaxed regulations — " 12 per cent, of phosphoric 

 oxide soluble in citric acid " is the minimum limit laid down hv 

 Regulation No. 11. On the other hand, it must be borne in mind 



