88 FORMATION OF ACID IN SOIL. 



Supposing the doctrine to be sufficiently established by my own 

 proofs offered above, it may be useful to trace the formation and 

 increase of acidity in different soils, according to the views which 

 have been presented, and to display the promise which that quality 

 holds out for improving those soils which it has heretofore rendered 

 barren and worthless. 



Every neutral soil at some former time must have contained cal- 

 careous earth in sufficient quantity to produce the uniform effect 

 of that ingredient of storing up and fixing fertility. [It was then 

 a calcareous soil, however small might have been the proportion of 

 free carbonate of lime contained.] The decomposition of the suc- 

 cessive growths of plants, left to rot on the rich soil, continually 

 formed vegetable acid, which, as fast as formed, united with the 

 lime in the soil. At last these two principles balanced each other, 

 and the soil was no longer calcareous, but neutral. Instead of its 

 former ingredient, carbonate of lime, it was now supplied with a 

 vegetable salt of lime. This change of soil does not affect the na- 

 tural growth, which remains the same, and thrives as well as when 

 the soil was calcareous j and when brought into cultivation, the 

 soil is equally productive under all crops suited to calcareous soils. 

 If the supplies of vegetable matter continue, the soil may even be- 

 come acid in some measure, as may be evidenced by the growth of 

 sorrel but without losing any of its fertility before acquired. The 

 degree of acidity in any one soil frequently varies ; it is increased 

 by the growth of such plants as delight to feed on it, and by' the 

 decomposition of all vegetable matters. Hence the longer a poor 

 field remains at rest, and not grazed, the more acid it becomes ; and 

 this evil keeping pace with the benefits derived, is the cause why so 

 little improvement, or increased product, is obtained from putting 

 acid soils under that mild treatment. Cultivation not only pre- 

 vents new supplies, but also diminishes the acidity already present 



of course I oppose ; deeming all acid products of soil, alone, as injurious to 

 fertility and productiveness of the land for useful crops. 



Besides the state of carbonate, Johnston says that lime exists in fertile 

 soils as chloride of calcium (muriate of lime), as sulphate, phosphate, 

 silicate, or humate of lime. " In combination with humic acid, lime exists 

 most frequently in soils which abound in vegetable matter in peaty soils, 

 for example, to which lime or marl have been added. * * * Few in- 

 vestigations have as yet been made in regard to the proportion of lime 

 which exists in the soil in the state of humate. It has generally been taken 

 for granted, either that a soil was destitute of lime, if it exhibited no sensible 

 effervescence with dilute muriatic acid, or, when further research was 

 made, and the quantity of lime rigorously determined, that the icJwle of this 

 Kme must have existed in the state of carbonate. That this is not necessarily 

 the case, however, appears to be proved by some recent examinations of 

 certain soils in Normandy, which contain as much as 14 to 15 per cent. 

 of lime, and yet exhibit no effervescence, and contain no carbonate. The 

 whole of the lime is said to be in the state of humate. (p. 230-1. 1819.] 



