ii4 Conservation of the Fertility or the Soil, [may, 



THE CONSERVATION OF THE FERTILITY OF 

 THE SOIL* 



A. D. Hall, M.A., F.R.S. 



Director of the Rothamstea Experimental Station. 



In considering the value of various systems of farming it 

 becomes a matter of prime importance to get some idea of 

 how far the fertility of the land is being preserved, and 

 whether the succeeding generation of farmers is likely to find 

 the cropping power of the soil improved or deteriorated by 

 the treatment it has received. It is pretty clear that in many 

 parts of the world the natural riches contained in the virgin 

 soils are being rapidly depleted ; this may be deduced from 

 the constant westward movement of certain classes of farmers 

 in the United States and Canada, though in some parts of 

 America the soil seems to be able to yield good crops for an 

 indefinite period ; on the other hand, many European soils 

 have reached a sort of constant level of production, and get 

 neither richer nor poorer, although they have been in cultiva- 

 tion for many centuries. We also occasionally hear of worn- 

 out soils, but it would be more correct to say badly managed 

 or spoilt soils, because there is no evidence that the produc- 

 tivity of a soil ever declines under suitable treatment. 



In tracing changes in the fertility of soil, we may content 

 ourselves with following up the changes in the amount of 

 nitrogen present, because though phosphoric acid, potash, 

 and lime are important factors in plant nutrition, these 

 elements are not susceptible to the gains and losses from 

 external operations like cultivation, by which the stock of 

 nitrogen is so greatly affected. 



There are various processes at work which will diminish 

 or add to the stock of nitrogen in the soil, and these may be 

 summarised as follows : — 



(i) The growth of plants simply removes some of the 

 nitrogen that has reached an available form, and if the crop 

 is taken off at harvest, there is so much direct loss to the 

 soil. As it may also be accepted that the plant itself, apart 

 from bacterial action, neither converts any of the combined 

 nitrogen it obtains into gas, nor brings into combination any 

 of the free nitrogen of the air, there is neither gain nor loss 



* An expansion of a paper by A. D. Hall and E. J. Russell read at the Winnipeg 

 meeting of the British Association, 1909. 



