ix.] LIMING 307 



action of lime as a liberator of potash is illustrated 

 by the effect of a dressing of chalk applied in 1881 

 to part of the permanent grass plots at Rothamsted ; 

 by 1884 differences began to be manifest, the chalk 

 caused a change in the herbage of those plots which 

 had been receiving potash each year for twenty-five 

 years previously, increasing the production as a whole, 

 and particularly increasing the proportion of leguminous 

 plants in the herbage. On the plots, however, which 

 had been receiving no potash, and therefore contained 

 no recently accumulated reserves of this material, the 

 chalk had practically no effect, either in the weight or 

 character of the crop. 



To some extent lime seems able to act as a liberator 

 of phosphoric acid in the soil. As pointed out by 

 Thenard, lime is able to act upon the very insoluble 

 phosphates of aluminium or iron which are present in 

 many soils, and, by converting them into phosphate of 

 lime, renders the phosphoric acid more available for 

 the plant. 



Besides its specific actions in thus rendering more 

 soluble the soil constituents which nourish the plant, 

 lime exerts a very beneficial action by maintaining 

 the neutral reaction of the soil ; it neutralises the acids 

 produced by the decay and nitrification (see p. 197) of 

 the organic matter in the soil. Again, as has been 

 shown already, it is necessary as a base to satisfy the 

 requirements of artificial manures like sulphate of 

 ammonia, superphosphate, and kainit (see p. 252), or 

 to prevent the soil being invaded by such organisms as 

 the destructive fungus causing " finger-and-toe " (see p. 

 244). It must, however, be clearly realised that lime 

 is wanted as a base, not as a compound of calcium, 

 necessary though calcium itself may be to the economy 

 of the plant ; and that only carbonate of lime (chalk, 



