XI.] MANURES FOR SWEDES 313 



industries. The point may be illustrated from the 

 Rothamsted experiments on the Agdell field, where 

 crops are grown in rotation with the following average 

 results : — 



Unmanured 16 cwts. 



Mineral only — Superphosphate and 

 Sulphate of Potash . . . . 208 „ 



Complete Manure — Nitrogen, Super- 

 phosphate, and Sulphate of Potash . 400 „ 



Without manure the yield is trifling, but with the 

 mineral manures (and the phosphoric acid is the 

 effective factor) the yield rises to 208 cwts. per acre, 

 although the land had been continually cropped without 

 any nitrogen supply ; lastly, when nitrogen also is 

 added, the yield becomes that of a high average crop 

 for the south of England. In practice, however, it is 

 found that where the land has been kept in good con- 

 dition and there has been adequate preparation of the 

 seed-bed, little or no manurial nitrogen will be required 

 to supplement the nitrates produced from the soil 

 reserves, and that consequently the great increase due 

 to the nitrogen in the experiments quoted will not be 

 reproduced under ordinary conditions of farming. 



In a large co-operative series of trials undertaken 

 by the Highland and Agricultural Society over the 

 whole of Scotland it was found that 84 lb. per acre of 

 sulphate of ammonia, or its equivalent in i cwt. of nitrate 

 of soda, was as much nitrogenous manure as could be 

 profitably employed. About 5 cwts. per acre of super- 

 phosphate, or 4 cwts. of basic slag, or 2 cwts. of steamed 

 bone flour, according to the soil, were indispensable ; the 

 superphosphate being best on loams and calcareous 

 soils, the basic slag on clays and peaty land, and the 

 steamed bone flour on sands and gravels. 



