414 SCIENCE PROGRESS 



change the reaction of the soil solution from distinctly alkaline 

 to strongly acid, while in practically all cases extracts prepared 

 with neutral salt solutions showed a higher H-ion concentration 

 than extracts prepared with water alone. Moreover, if a soil 

 is extracted with Na-acetate solutions of varying concentration 

 it has been found that the amount of acetic acid liberated 

 increases, while the actual hydrogen ion concentration in the 

 resulting solution diminishes as the concentration of the 

 Na-acetate increases. If the extraction is carried out with 

 Na-acetate and NaCl solutions of equivalent strengths then 

 more titratable acid is hberated in the former case, but a 

 higher hydrogen-ion concentration is attained in the latter. 



Distinction between Acidity and Lime Requirements 



OF A Soil 



Evidently more factors than mere acidity are involved 

 here ; the absence or deficiency of certain bases from the soil 

 brings about a condition of infertility that cannot be accounted 

 for as being due directly only to a definite degree of acidity of 

 the nutrient soil solution. Such a condition of infertility is 

 remedied by a dressing of lime. But for the complete removal 

 of this condition an amount of lime is added in excess of that 

 required for neutralisation purposes, and it is generally assumed 

 that this excess of lime is necessary in order to neutralise any 

 acidity that may develop subsequently. It must be emphasised, 

 however, that this excess of free lime probably has certain bene- 

 ficial effects on the soil in addition to its effect on the reaction, 

 and it would appear that the presence of a free base — or rather 

 an available base, for lime quickly reverts to carbonate in the 

 soil, in which form it is certainly not a free base although it is 

 as available as though it were actually free — is of considerable 

 importance in maintaining soil fertility. 



Effects of Acidity and of Liming on the General 



Fertility of the Soil 



Thus the presence of an excess of free lime appears to have 

 a good effect on the physical condition of heavy soil due to the 

 flocculating action of CaH2(C03)2 or of Ca(0H)2. This effect 

 indirectly influences the regulation of the air and moisture 

 supplies, which in their turn affect the conditions underlying 

 the biological and chemical relationships : both nitrification 

 and nitrogen-fixation are promoted, the rate of oxidation of 

 organic matter is increased,^ and it is supposed by some that 



^ This is denied by Maclntire as a general proposition, although it may be 

 true in some cases. 



