WHEAT. 191 



0.140. Then, referring to the results obtained in the wheat- 

 field itself, it is seen that after growing wheat with full 

 mineral and nitrogenous manure since 1843-44, the percen- 

 tage of nitrogen in the dry sifted surface-soil was — in 1865, 

 0.1230, and in 1881, 0.1264; but with mineral manure 

 without nitrogen, it was — in 1865, only 0.1119, and in 1881, 

 0.1012 per cent; and lastly, without manure from the com- 

 mencement it was — in 1865, only 0.1090, and in 1881, 0.1045 

 per cent. That is to say, with mineral and nitrogenous 

 manure, the percentage of nitrogen was the highest, and 

 rather higher at the later than at the earlier date ; the 

 result being due, as has been proved, not to the accumula- 

 tion of manure-residue, but of crop-residue. On the other 

 hand, with mineral manure without nitrogen, or without any 

 manure at all, the percentage of nitrogen was lower than 

 when nitrogenous manure was also used, and in each case 

 it was lower at the later date — that is, as the exhaustion 

 progressed. 



On a consideration of these various results, it may perhaps 

 fairly be concluded that the percentage of nitrogen in the 

 surface-soil of the wheat-field at the commencement was 

 certainly higher than in 1865 or 1881, under the conditions 

 of nitrogen-exhaustion with mineral manure alone, or with- 

 out any manure at all ; and that it was about as high as 

 where nitrogenous as well as mineral manure had been 

 annually applied ; probably, therefore, from 0.1250 to 0.1300 

 per cent, and probably nearer the lower than the higher 

 figure. 



Looking to the other results in the table relating to 

 Eothamsted soils, it is seen that with barley, as with wheat, 

 when grown year after year with mineral manures alone, the 

 percentage of nitrogen in the surface-soil was low, with a 

 tendency to decline from time to time ; and lastly, after roots 

 grown with mineral manure alone, the percentage is lower 

 still — indeed lower than has been found where any other crop 

 has been grown under similar conditions. Then it is further 

 seen, that in the case of various arable fields laid down to 

 permanent grass, the percentage of nitrogen increased more 

 or less according to the time it had been laid down — the 

 figures at the different periods being 0.1235, 0.1509, 0.1740, 

 0.2057, and 0.1943 ; whilst the percentage in very old grass- 

 land was 0.2466. 



Next, in various arable soils in Great Britain, the percen- 

 tage of nitrogen in the surface-soils ranged from 0.107 to 0.220. 

 Compared with these, the percentage in various United States 

 and Canadian prairie soils ranged from 0.187 to 0.618 ; the 

 greater number showing about 0.30 per cent. Lastly, a num- 



