27 



Two different effects of lime are studied^ its sterilising action and its 

 power of neutralising acidity. Sterilisation is effected when so much 

 lime has been added that an aqueous extract of the soil is alkaline to 

 phenolphthalein ; chemical, bacteriological and physiological tests 

 all closely agree. This can be effected by lime only ; the carbonate 

 is of no use for the purpose. 



Neutralisation, however, requires much less lime, and can equally 

 be brought about by the carbonate. The amount necessary is indicated 

 by the adsorptive capacity of the soil for calcium bicarbonate. 



A definite connection was traced between soil reaction and natural 

 flora on soils of the same type and similarly situated ; for example, in 

 making a close survey of Harpenden Common the following plants 

 were dominant in patches of differing lime requirements, clover appear- 

 ing only where the need for lime was small, Yorkshire fog and finally 

 sorrel where the need was great : — 



LIME REQUIREMENTS AS RELATED TO VEGETATION. 



Dominant Flora. 



Trifolium repens (wild white clover) 



Festuca ovina and rubra 



Mixed. Achillea Millefolium, Luzula 



and moss. 

 Ulex europcBus (gorse) 

 Holcus lanatus (Yorkshire fog) 

 Rumex Acetosa (sorrel) 



XIII. " The Effect of Removing the Soluble Humus from a Soil on 

 its Productiveness.'* William Weir. Journal of Agricultural 

 Science, 1915. 7, 246-253. 



A large quantity of soil was divided into two portions ; one was 

 treated with dilute hydrochloric acid and repeatedly extracted with 

 dilute caustic soda solution so as to remove soluble humus ; the other 

 was left untouched. Chalk was added to the treated soil to make the 

 carbonate content equal to that of the untreated soil ; the soils were 

 then put into pots and sown with four crops in succession : wheat, 

 mustard, rye, and finally mustard again. In each case the yields, 

 both of dry matter and of nitrogen, were approximately the same for 

 the untreated and the treated soils, in spite of the circumstance that 

 the extraction had removed 40 per cent, of the nitrogen from the soil. 



Laboratory experiments were also made to ascertain the effect of 

 the extraction on the production of ammonia and nitrates in the soil. 

 It was found that the extraction increased the bacterial numbers and 

 ammonia accumulation, but diminished nitrate production, though 

 the sum of ammoniacal and nitric nitrogen is usually less in the extracted 

 than in the untreated soil. These results agree with those obtained 

 by W. Buddin, when soils were treated with non-volatile antiseptics 

 (Report for 1914, p. 12), and they suggest that one result of the 

 extraction process is partially to sterilise the soil. 



