32 The Rothamsted Wheat Experiments. 



the use of artificial nitrogenous manures, under the circum- 

 stances and in the degree in which they are generally 

 employed in the ordinary course of agriculture in this 

 country, remains to be considered. But it seems desirable 

 to notice here what is said on the subject of the unexhausted 

 residue of manures in the report of the second twenty years' 

 experiments, for which the results obtained on plots 16a and 

 166 afford the necessary data. From 1852 to 1864 inclusive, 

 these plots received mixed mineral manure and 8001b. of 

 ammonia-salts per acre per annum, containing 1721b. of 

 nitrogen. It is very rarely that a sufficiently large crop of 

 wheat is grown to remove one-half of this quantity of 

 nitrogen. In 1863 and 1864 the seasons were highly favour- 

 able for the growth of wheat ; and, as the size of the crop is 

 regulated very much by the amount of nitrogen at its 

 disposal, the two seasons were well adapted for ascertaining 

 how much of this very large application would be employed 

 in the growth of the crop. In 1863, plot 16 gave 56 bushels 

 per acre ; in 1864, 51 bushels per acre. But plots Sa and 86 

 produced 56 bushels and 50 bushels in the same two years, by 

 means of an application of 6001b. of ammonia-salts ; and, as 

 the additional 200lb. supplied to 16a and 166 only added one 

 bushel to the crop, it was quite evident that the possible 

 limits of growth on 8a and 86, even in seasons so favourable, 

 had been reached. All further manuring was, therefore, 

 stopped after 1864, with the view of obtaining information, 

 which might prove to be very valuable, in regard to the 

 unexhausted residue of the manure employed. 



Table III. shows the produce of plot 16 for the last two 

 years during which it received manure, and for the nineteen 

 succeeding years during which it was unmanured ; also for 

 comparison there is given the produce of plot 5, which 

 received an annual dressing of minerals alone over the whole 

 period. 



It will be noticed that in the first year after the manures 

 were stopped, the produce of plot 16 was 18 bushels more 



