vni] RECLAMATION OF THE MOOR 121 



and has thus opened up the possibility of raising 

 potatoes and cereals more cheaply than before. 



An interesting piece of reclamation went on under 

 Nilsson's direction in Gothland, Sweden. More than 

 30,000 hectares of the island consisted of barren 

 swamps, and yet the soil was rich both in lime and 

 in nitrogen. Nilsson showed that the limiting factor 

 was lack of phosphorus. The ground was therefore 

 drained and treated with phosphatic manure ; it then 

 yielded excellent crops of corn, rape and sugar beet. 

 Instead of depending wholly on foreign supplies of 

 phosphates, investigation was made by Wiborgh of 

 the iron ore occurring in Northern Sweden and known 

 to contain calcium phosphate : a method of extraction 

 was devised and quantities of this Wiborgh phos- 

 phate were produced at Lulia. Subsequently a 

 cheaper process was worked out by Palmaer. 



In the Isle of Ely phosphates are also found to be 

 the limiting factor and dressings of superphosphate 

 result in marked crop production ; elsewhere, however, 

 potassium compounds constitute the limiting factor. 

 A well-known example is furnished by the Momence 

 experimental field set out by Dr Cyril Hopkins in 

 Illinois, where potassic fertilisers yield good crops but 

 other fertilisers prove useless. Dr Hopkins 1 tells 

 a pathetic story of a settler who spent years of un- 

 availing labour on some of this black soil and did not 



1 The Story of the Soil, Boston, 1912. 



