38 The Rothamsted Wheat Experiments. 



12 to 13 bushels per acre. As the Rothamsted soil certainly 

 contains a very much less stock of fertility than the soils 

 upon which wheat is extensively grown in other countries, 

 it is impossible to attribute the comparatively large yields 

 there to any other cause than to the clean state of the land. 

 The amount of food at the disposal of the crop is small, 

 but it is not shared to any great extent with other plants. 

 The large produce of both wheat and barley on the 

 unmanured land in the Woburn experiments also shows how 

 much the crops grown upon the ordiuary cultivated land 

 of this country are reduced by weeds. It is true that weeds 

 do not exhaust a soil, as, in their decay, the fertility which 

 they have taken up becomes again available ; but they take 

 up nitrates, which, during their growth, revert to the form of 

 organic nitrogen (that is, nitrogen, combined with carbon), 

 and this must undergo nitrification in the soil before becoming 

 again available as plant food. Considering the high price 

 paid for active nitrogen,' as in salts of ammonia or nitrate 

 of soda, a serious loss is incurred if this nitrogen goes to 

 promote the growth of weeds, as so much time must elapse 

 before it is again available as food for a future crop. 



CONTINUOUS GROWTH OF WHEAT UPON THE 

 SAME LAND WITH MINERAL MANURES 

 ALONE. 



The plot which received mineral manures alone next claims 

 consideration. Bearing in mind the fact that uniformity of 

 manuring was not resorted to on all the plots till after the 

 expiration of eight years, the remaining thirty -two years 

 of the total forty may be conveniently divided into four 

 periods of eight years each. In Table V. the corresponding 

 results on the unmanured plot are given for the sake of 

 comparison. 



During the first eight years (1844-1851) plot 5 received 



