242 SOIL CONDITIONS AND PLANT GRO WTH 



TABLE LXV. LIME REQUIREMENT AS RELATED TO VEGETATION. 



Similarly there is a close relation between the micro- 

 organic flora and the sourness of the soil. Christensen (670) 

 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 2 found 

 nitrification going on slowly in the Rothamsted grass plots 

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

 so acid that only a few species of plants survive. 



1 The culture solution contains no CaCO 3 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. 



