KESIDUES LEFT BY MANURES 



205 



subsequent crops in each course being grown without further 

 manure. We thus obtain a means of ascertaining what residue 

 is left in the land after the removal of the crop to which the 

 manure has been applied. If, for example, we compare the 

 plots receiving minerals only with those receiving minerals and 

 nitrogen, on the fallow portion the addition of nitrogen produces 

 an increase of crop from 186 to 443 cwt. per acre, or of 131 

 per cent. This crop of roots is entirely removed, but the suc- 

 ceeding barley crop shows a total produce of 2783 Ib. on the 

 plot where nitrogen was applied to the roots, against 1970 Ib. 

 on the plot without nitrogen ; thus the residue of the nitrogen 

 in the ground after one crop had been grown and removed was 

 still able to increase the next crop by 41 per cent. 



The following Table (LXX.) shows the summarised results 



TABLE LXX. Crops grown in rotation, Agdell Field. Total produce per 

 acre. Mean of seven Courses, 1884-1911. Increase due to Nitrogenous 

 Manures applied to the Swede Crop only, and their Eesidues. 



for the last seven courses on both the fallow and the clover 

 portions. 



It will be seen that a nitrogenous dressing consisting of 

 rape cake and ammonium-salts leaves in the ground, after 



