242 SOIL CONDITIONS AND PLANT GEO WTH 



Table LXV. — Lime Requirement as Related to Vegetation. 



Harpenden Common. Hutchinson and McLennan (1401^). 



Average Lime Requirement of Soil. 



Approx. o*22 per cent. CaCOj 

 0*26 ,, 

 o'3i ■, 

 0-39 

 o"43 



o'53 



Dominant Flora. 



Wild white clover 

 (Trifolium repens) 



Fescues (F. ovina and 

 rubra) 



Mixed, Yarrow, wood- 

 rush and moss 



Gorse 



Yorkshire fog. 

 Sorrel 



Woods. Salisbury, 242. 



Lime 

 Reqt. 



0*24 



0-52 

 0*62 



Mercurialis 



rHolcus, 

 \ Antkoxanthum, 

 ^Cnicus 

 (Holcus 

 \ Anenome 



Similarly there is a close relation between the micro- 

 organic flora and the sourness of the soil. Christensen {6ya) 

 found that azotobacter was especially sensitive, its occurrence 

 depending sharply on a sufficiency of base : so much so, 

 indeed, that he uses the presence or absence of azotobacter as 

 a test of the need of adding^lime to soil. The test is generally 

 adopted in Denmark. Some of his results are as folio ws : — 



Nitrifying organisms are also sensitive : they still occur 

 even in acid soils, but their activity becomes much more 

 marked after adding lime. Hall, Miller, and Gimingham^ found 

 nitrification going on slowly in the Rothamsted grass plots 

 receiving 600 lb. of ammonium salts annually, and now become 

 so acid that only a few species of plants survive. 



1 The culture solution contains no CaCO- but is inoculated with the soil 

 only. Hence the experiment demonstrates the sufficiency or otherwise of the 

 CaCO, in the soil for the needs of the organism. A parallel test is made using 

 the full culture solution so as to show whether the organism is present in cases 

 where negative results are obtained. 



"^Proc. Roy. Soc, 1908, 80 B, 196-212. 



