198 The Rothamsted Grass Experiments. 



more than from 10 to 15 per cent, of the nitrogen, supplied 

 in the farmyard manure, recovered in the increase of crop 

 during the years of application. 



In the case of the barley experiments, after the farmyard 

 manure had been applied for twenty years in succession, the 

 plot was divided. To one-half the dung was still annually 

 applied, but the other was now left without any further 

 manure. The result as to the recover} of the nitrogen of the 

 manure in the two cases is recorded in a table which is 

 not reproduced here. The figures indicate, however, that over 

 the twenty years of the application (on the whole plot) 10' 7 per 

 cent, of the supplied nitrogen is so estimated to be recovered 

 in i he increase of the crop ; over the next six years of the 

 continued application, on half the plot, 15*7 per cent ; and 

 over the total period of twenty- six years 11/8 per cent. On 

 the other half there was the 10'7 per cent, of the twenty 

 years' supply recovered during the twenty years, 2*9 per cent, 

 more of it during the next six years, and in all 13'6 per cent, 

 of the twenty years' supply recovered in the twenty-six years. 

 That is to say, of 40141 b. of nitrogen estimated to be supplied 

 in the twenty years, 86'4 per cent., or 34681b., remained 

 unaccounted for in the increase of crop at the end of the 

 twenty-six years. 



As only 2'9 per cent, of the original supply of nitrogen 

 was recovered in the first six years after the application of 

 the manure ceased, or, say, O5 per cent, per annum, it would 

 obviously take from one hundred and seventy to one hundred 

 and eighty years to recover the whole of the 89'3 per cent. 

 (=100 10*7) which remained, if at the same rate as during 

 the first six years. There can be little doubt, however, that 

 part of the unrecovered amount has been lost by drainage or 

 otherwise, arid that, whatever residue remains, a gradually 

 decreasing proportion of it will be annually recovered. 



With regard to the wheat plots, samples of the soils have 

 been taken, and their nitrogen estimated, with the view of 

 determining whether or not the whole of the unrecovered 



