BACTERIA IN THE SOIL l6l 



some of the nitrogen drained from it. But such manuring 

 cannot keep pace, according to Sir W. Crookes, with the 

 present loss of fixed nitrogen from the soil. We have al- 

 ready referred to several ways in which " loss " of nitrogen 

 occurs. To these may well be added the enormous loss oc- 

 curring in the waste of sewage when it is passed into the 

 sea. As the President of the British Association pointed 

 out, 1 the more widely this wasteful system is extended, 

 recklessly returning to the sea what we have taken from the 

 land, the more surely and quickly will the finite stocks of 

 nitrogen, locked up in the soils of the world, become ex- 

 hausted. Let us remember that the plant creates nothing 

 in this direction ; there is nothing in wheat which is not 

 absorbed from the soil, and unless the abstracted nitrogen 

 is returned to the soil, its fertility must be ultimately ex- 

 hausted. When we apply to the land sodium nitrate, sul- 

 phate of ammonia, guano, and similar manurial substances, 

 we are drawing on the earth's capital, and our drafts will 

 not be prepetually responded to. 2 We know that a virgin 

 soil cropped for several years loses its productive powers, 

 and without artificial aid becomes unfertile. For example, 

 through this exhaustion forty bushels of wheat per acre 

 have dwindled to seven. Rotation of crops is an attempt 

 to meet the problem, and the four-course rotation of turnips, 

 barley, clover, and wheat witnesses to the fact that practice 

 has been ahead of science in this matter. 



The store of nitrogen in the atmosphere is practically 

 unlimited, but it is fixed and rendered assimilable only by 

 cosmic processes of extreme slowness. We may shortly 

 glance at these, for it is upon these processes, plus a return 



* British Association for the Advancement of Science, Bristol, 1898, Presi- 

 dential Address. 



2 Sir John Lawes and Sir Henry Gilbert (Times, December 2, 1898), have 

 pointed out that the addition of nitrates only would be of no permanent use to 

 the wheat crop. They rely upon thorough tillage and proper rotation of crops 

 as the means of improving the nitrogen value of the soil. 



