2t2 ' P ARM YARD MANURE [chap 



where four crops in rotation are grown after each 

 application of farmyard manure, out of 207 lb. "of 

 nitrogen supplied as dung made from roots and hay 

 alone 144 lb, were recovered in the three following 

 years, and of 257 lb, supplied as cake-fed dung 158 lb. 

 were similarly recovered. 



The extremely lasting character of those nitrogenous 

 compounds in farmyard manure which are not recovered 

 in the first year is illustrated in an exceptional manner 

 in the Rothamsted experiments. On the grass land, 

 for example, one plot received 14 tons of dung per 

 acre per annum for eight years (1856-63) and then was 

 left unmanured. Table LXV. shows that it has con- 

 tinued to give a larger crop than the unmanured plot 

 alongside for more than forty years. The table shows 

 that in the first year after the application of farmyard 

 manure had been stopped the plot with the residues of 

 the previous eight years' manuring gave double the yield 

 of the unmanured plot ; in the following year the yield 

 was still double ; but from that time its superiority has 

 slowly declined, though for the last ten years it has 

 still amounted to 1 5 per cent. 



A similar experiment was made on the barley plots, 

 one of which received 14 tons per acre of farmyard 

 manure for twenty years from 1852 to 1871, and has 

 since been left unmanured. Table LXVI. shows the 

 yield from this plot, from the unmanured plot, and from 

 the plot which has continued to receive 14 tons of 

 farmyard manure every year, for the years immediately 

 following the discontinuance of the dung and for 

 successive five-year periods since. It will be seen 

 that though the yield has fallen continuously to about 

 40 per cent, of that of the continuously dunged plot, 

 it still remains more than double that of the wholly 

 unmanured plot. 



