THE COMPOSITION OF THE SOIL 119 



be set out in order of their calcium carbonate content by the 

 usual analytical methods, or of their lack of calcium carbonate 

 by one of the lime requirement methods. 1 Before any indi- 

 cation can be given of the amount of lime required for cultiva- 

 tion it is necessary to make field trials (p. 335). 



In general, sandy soils require only sufficient calcium 

 carbonate to prevent sourness, while clay soils need in addi- 

 tion enough to keep the texture good. Sands well supplied 

 with calcareous water and under ordinary arable cultivation 

 may get along with cri per cent, or even less calcium carbon- 

 ate. Many light soils that are intensively farmed respond to 

 dressings of chalk or of ground limestone, even though 0-2 

 or 0*3 per cent is already present. 0*5 per cent, of calcium 

 carbonate commonly proves insufficient for clay soils, and 

 even ro per cent, may not be enough in highly-farmed 

 districts, especially where cattle are fed on the land and tread 

 the soil into a somewhat sticky state. Further increases in 

 calcium carbonate over and above the proper amount are not 

 known to have any effect except to provide a margin of safety. 

 Considerable work has been done on the effect of lime on peat 

 soils, which seems to be more than a neutralisation of acidity. 

 Oden (218^) suggests that the calcium humate produced may 

 be directly beneficial to plants. 



Calcium carbonate is not a permanent constituent of the 

 soil, but changes into the soluble bicarbonate and washes out 

 into the drainage water ; the average loss per acre per annum 

 throughout England and Wales has been estimated at 500 lb., 

 and at Rothamsted on the arable land at 800 to 1000 lb. 

 (i2O<$). The rate of loss is influenced by the treatment, being 

 increased by the use of ammonium sulphate and decreased by 

 dung and by a growing crop ; it is much less on pasture than 

 on arable land. Repeated additions of calcium carbonate to 



1 Such as Veitch's (287) or Hutchinson and McLennan's (140^). L. J. Wild, 

 y. Ag. Sci., 1917, 8, 154, shows that the latter when modified by a correction 

 factor of 0*1 per cent, proves helpful in the study of New Zealand soils. For 

 a critical account of the various methods see Ames and Schollenberger (4) and 

 E. A. Fisher (99). It is hardly necessary to point out that the " lime require- 

 ment" measures something entirely distinct from- the PH value (p. 115). 



