vm.] 



MAINTENANCE OF FERTILITY 



IS9 



the dormant stock of potash to obviate the necessity 

 of any specific potash manuring: on the light soils 

 200 lb. of kainit per acre once during the rotation would 

 repair all losses. As regards the nitrogen, however, the 

 figure we have obtained possesses very little value as a 

 guide to practice, because it ignores the whole group of 

 gains and losses of nitrogen which are due to bacteria in 

 the soil. For example, we have assumed that the 

 nitrogen contained in the clover crop has all been 

 derived from the atmosphere, so that this crop has 



Table XVI.— Fertilising Constituents per Acre Removed 

 DURING Four-Course Rotation. 



* Nitrogen drawn trom atmosphere and not added In. 



entailed no loss to the soil ; but we have very sound 

 evidence that the soil will have gained nitrogen after 

 the growth and removal of the clover crop. Moreover, 

 half the nitrogen in the clover-hay fodder is returned to 

 the soil in the dung, whereby the farm will have been 

 still further enriched by the growth and consumption of 

 clover. On the other hand, the soil suffers losses of 

 nitrogen which cannot be estimated — losses both by 

 drainage and by bacterial action — and these losses grow 

 larger the higher the level of richness at which the land 



