WHEAT. 177 



form of ammonium-salts is evident. In other words, nitrogen Ammon- 

 applied as ammonium-salts in any one year was practically iw f-aaU* 

 exhausted that year, in the crop, or otherwise ; leaving prac- inoneyear. 

 tically none for subsequent action. Lastly, in regard to plots 

 17 and 18, it is seen that the average produce over 40 years 

 of the ammonium-salts succeeding the mineral manure is 

 30^- bushels, or exactly twice as much as that of the mineral 

 manure succeeding the ammonium-salt. 



Again, plot 16 received annually for 13 years, 1852-64 Yiddfrom 

 inclusive, mixed mineral manure and ammonium-salts con- hea ?y " man ' 

 taming a double quantity (172 lb.) of nitrogen j then for 19 U 

 years, 1865-83, it was left unmanured ; and then, for the crop 

 of 1884 and each year since, it has received mixed mineral 

 manure and sodium-nitrate containing 86 lb. of nitrogen. 

 During the 13 years of heavy manuring there was a large 

 yield, in two cases exceeding 50 bushels, with an average for 

 the 13 years of 39| bushels. 



The first 3 of the succeeding years during which no manure Result of 

 was applied, the average yield was only 21 § bushels, a de- '>? ithhold - 

 crease of nearly one-half, followed in the succeeding two U re. 

 periods of 8 years each by average yields of 16f and llf 

 bushels ; against, for the corresponding periods on plot 3, con- 

 tinuously unmanured, 12£ and 10| bushels. Or, taking the 

 average of the 19 years of yield without manure on plot 16, 

 we have 14| bushels, against, over the same years, 13| 

 bushels on plot 5 with mineral manure only since 1852, and 

 llf bushels on plot 3, unmanured since 1839. It is fair to 

 presume, moreover, that some of the greater yields of plot 16 

 over that of plot 3 from 1865-83, were due to the residue of 

 the mixed mineral and excessive nitrogenous manure, but 

 perhaps mainly, as will be seen further on, to increased crop- 

 residue. 



Since the re-commencement of the manuring to plot 16 for Manuring 

 the crop of 1884, however, the plot has given some heavy resumed - 

 yields, notably in 1886 and 1891 ; and the average for the 8 

 years, 1884-91, was 37£ bushels, or only If bushel less than 

 on plot 2, which has received 14 tons of farmyard manure 

 per acre each year for the last 51 years. 



If, as the above results have demonstrated, there is practi- what be- 

 cally little or no available residue from previous application c ^^^ 

 of ammonium-salts, the question arises, What becomes of nitrogen? 

 the nitrogen of the manure not taken up by the immediate 

 crop ? This point is illustrated by the results given in Table 

 50 (p. 178). The plots there tabulated all received the same 

 amount of nitrogen in manure, but with different mineral 

 manures, and they are given in the order of their average 

 annual increased yield of nitrogen in the crops over plot 5, 



VOL. VII. M 



