3o6 SOIL CONDITIONS AND PLANT GROWTH 



is that two conditions come in : wetness and acidity — from 

 both of which chalk soils are free ; the so-called calcicolus 

 plants will, however, grow elsewhere if these conditions are 

 absent ; thus he finds beech on non-calcareous soils on the 

 continent so long as these soils are dry. Dr. Brenchley finds 

 that the calcifuges of the West of England are not all calci- 

 fuges in the Eastern counties, while Massart ^ showed that 

 the typical calcifuge, Calluna vulgaris , grows on the " lime- 

 stone pavements " of the West of Ireland. 



The fact that a calcareous rock lies beneath is no proof 

 that the soil itself is calcareous : on the contrary, the soil may 

 often contain practically no calcium carbonate, either because 

 it has become decalcified by rain, or because it really represents 

 some deposit of wholly extraneous origin. 



The agricultural value of chalk soils depends very largely 

 on their depth, and is much greater in valleys where the soil 

 and water collect than on the higher ground where the soil is 

 thinner. The two defects most in need of remedy are the lack 

 of organic matter and the tendency to become light ; these 

 are met by additions of dung or other organic manures, by 

 rolling and. cultivating with heavy instruments, and above all 

 by feeding animals on the land with the crops actually growing 

 there and with purchased food, a process known as "folding". 

 Heavy wooden ploughs are still in use, and until recently 

 were worked in many places by large teams of heavy oxen. 

 Sheep are by far the most suitable animals to be fed on the 

 land, and they form the centre round which the husbandry of 

 chalk districts has developed ; indeed, so important are they 

 that each chalk region has evolved its own breed of sheep 

 — South Downs, Hampshires, etc. As fertilisers potassic 

 manures, especially kainit, are generally profitable ; superphos- 

 phate is needed for turnips, and in wet districts basic slag is 

 useful on the grass land. Skilful cultivation is always neces- 

 sary, or the soil dries into hard, steely lumps that will not 



^ Brit. Assoc. Report, 1911, 564. The case of Calluna is discussed by M. C. 

 Rayner in Annals of Botany, 1915, 29, 97-133, and Sphagnum by M. Skene, 

 ibid., 191 5, 29, 65-87. 



