H. B. Hutchinson and K. MacLennan si 



Part II. Lime Requirements for Neutralisation Purposes. 



By far the most frequent purpose for which lime is employed in 

 agricultural practice is the correction of ''soil acidity," whether this is 

 due to the presence of purely mineral soil constituents, to the application 

 of acid artificial fertilisers, or to the accumulation of organic residues 

 evidenced by more or less pronounced peat deposits. The condition is 

 indicated in the field by the occurrence of certain " calcif ugous " 

 plants, e.g. Rumex acetosella. Chrysanthemum segetum, Spergula arvensis, 

 and Scleranth'us annuas, by the repeated failure of leguminous 

 crops such as clover and lucerne, or by the incidence of "finger 

 and toe" in cruciferous croiDS. Dechuing fertiUty of the soil gradually 

 becomes evident, although this is subject to variation with the different 

 crops — such crops as barley, wheat and clover being more, and oats, 

 rye, millet, buckwheat and potatoes less sensitive, to soil acidity. 



In the laboratory various tests have been employed for indicating 

 the desirabihty of lime applications, and these may be divided into two 

 classes according as to whether they indicated (a) the presence of a 

 sufficiency of bases, usually calcium, or {h) lack of bases or soil acidity. 



General Methods for indicating Lime Reserves m the Soil. 



Of the various methods designed to indicate the presence of an 

 adequate supply of base, those for the determination of free carbonates 

 have been most generally adopted. These methods have, however, 

 often diftered greatly in procedure and the results do not admit of 

 direct comparison in the majority of cases. Neglecting this fact, certain 

 standard carbonate contents have been suggested, but the evidence in 

 favour of these is very meagre, resting as it does chiefly on the observed 

 fact that soils containing 0-5-1-0 per cent, calcium carbonate are 

 generally fertile, other conditions being normal, although closer inquiry 

 shows that many soils are devoid of carbonate and are still quite pro- 

 ductive. The method has the advantage, however, of indicating the 

 amount of hme present in a form capable of limiting soil acidity, whilst 

 this can by no means be claimed for other methods where the amount 

 of Hme extractable by various solvents is calculated as carbonate. 

 HoUemann (7) proposed extraction of the soil with water saturated with 

 carbon dioxide and estimation of the lime removed ; where the amount 

 of Ume thus extractable from a clay soil fell below 0-15 per cent. (CaO) 

 a benefit might be expected from Hming. 



Joum. of Agrio. Sci. vii 6 



