238 



Phosphatic Fertilisers. 



[June, 



though the rainfall is not particularly high, slag has improved 

 the yield of hay, raising it from 10 cwt. per acre on the 

 unmanured to 20 cwt. per acre on the slagged land in 

 one of the poorest fields, and from 30 cwt. on the un- 

 manured to 40 cwt. per acre on the slagged land in one of the 

 best fields. Here also the chief improvement is in the type of 

 herbage ; the clover increases considerably, and the land is more 

 completely covered with vegetation, with the result that its tem- 

 perature is lower in summer, there is less wastage of water by 

 evaporation, and in consequence the crop has a larger available 

 supply of water. 



Basic slag does not produce these striking results on all types 

 of grass land. Where the herbage is already good enough to 

 carry three, four or more sheep per acre each season there is 

 less room for improvement; this is the case at Rothamsted. and 

 in consequence the grazing experiments are less impressive than 

 at Cockle Park. Similarly the yield of hay on the unslagged land 

 is above that on most Essex slagged plots; hence the improve- 

 ment is less marked. Further, on light land there is sometimes 

 only little improvement until kainit is added; the combination 

 of slag and kainit then gives a better herbage and larger yields, 

 but there is not always a profit. So on hill land the value of 

 the improvement effected by the slag does not always repay the 

 cost to the farmer; the fault here is not always with the slag, 

 but sometimes with the system of management of the grazing. 



On Arable Land. — Although basic slag is best known for its 

 effects on grass land it has in many cases proved useful on arable 

 land also. In the north of England and in Scotland it is recom- 

 mended for use on swedes and turnips, either in partial or com- 

 plete replacement of superphosphate, especially where finger- 

 and-toe is common. In the south and west of England it has 

 not generally given as large crops as superphosphate, though 

 under favourable conditions of price it has sometimes, proved 

 equally profitable. 



Types of Slag.— There are at present three types of slag on 

 the market. (1) The old Bessemer slag with which the Cockle 

 Park experiments were carried out. This contains total phos- 

 phorus equivalent to 38 to 42 per cent, of tricalcic phosphate, 

 with a solubility of 85 per cent, by the official citric acid test. 

 Nowadays this type of slag is not common, but a certain amount 

 is still produced in this country, and some is imported from 

 abroad. It seems, however, improbable that large supplies will 

 be maintained. 



