152 Fertilisers [pt. hi 



Comparison of basic slag and superphosphate. On 

 heavy clays, on downland pasture and in wet situations 

 slag is generally better than superphosphate. For roots, 

 potatoes, hops and other short season crops superphos- 

 phate is usually better than slag. In Hendrick's swede 

 experiments! at Aberdeen there was little to choose 

 between them, though for equal amounts of phosphate 

 apphed superphosphate gave on the whole shghtly 

 larger increases in crop,' but where finger and toe was 

 prevalent it required the addition of lime. In the Irish 

 experiments equal weights of basic slag and super- 

 phosphate gave approximately equal results^. Some of 

 the Yorkshire experiments giving the same result are 

 set out on p. 162. From these and other experiments we 

 may conclude that the two fertilisers are nearly equally 

 effective and that the choice between them must turn 

 on special circumstances such as climate, the wetness, 

 heaviness, etc., of the land. It is not uncommon or un- 

 wise to apply both to the soil separately, not mixed. 



Other phosphates 



From time to time other attempts have been made to 

 utilise natural phosphates by converting them into more 

 readily soluble compounds, the most interesting of which 

 are those of Wilborgh and of Palmaer, both of the Poly- 

 technic Institute of Stockholm. Large quantities of im- 

 pure natural phosphates are obtainable from the North 

 of Sweden, which Wilborgh attempted to utilise by 

 fusing with sodium carbonate. The product was good, 

 but too costly. Palmaer adopted an electrolytic method, 



1 Aberdeen College, Bull. Nos. 1, 4 and 8, 1904, 1906, 1907. Also 

 Trans. Highland and Agric. Soc., 1906.' 

 * Journ. Dept. Agric, Ireland, 1913. 



