616 
Rotation of Crops. 
besides a full supply of mineral constituents, about 140 lb. ot 
nitrogen ; at the average rate, therefore, of 35 lb. per acre per 
annum over the four years. But, in the case of the continu- 
ously grown wheat crops, not only a full supply of mineral 
manure, but 43 lb. of nitrogen as ammonium-salts, were directly 
applied every year. The fact of the greater amount of produce on 
the rotation plots would indicate, therefore, that notwithstanding 
the growth and removal of the intermediate crops since the ap- 
plication of the manure for the roots, there was more nitrogen, and 
more of other constituents also, in a condition of composition and 
of distribution available for the wheat, than in the case of the 
annual direct supply. 
Of course, the proportion of grain and of straw in a wheat 
crop varies, as it also does in barley, according to variety, soil, 
season, and other circumstances. It is seen that, in the experi- 
mental crops, whether grown in rotation or continuously, there 
was always much more of the produced dry matter accumulated 
in the straw than in the grain. Indeed, there was in some cases 
nearly twice as much. On the assumption, therefore, that as a 
rule the grain will be sold, and the straw retained on the farm 
as food and litter, very much more than half of the produced 
dry matter will be so retained. 
Comparing the amounts of dry matter accumulated in the 
different rotation crops, and taking as the most normal the 
quantities obtained under the influence of the mixed manure, 
including nitrogen, it is seen that, on the average, the two cereal 
crops — the barley and the wheat — produced approximately equal 
amounts ; and each considerably more than either of the fallow 
crops — the roots or the Leguminosae. 
The Amounts of Nitrogen in the Rotation, and in the Continuous 
Crops. 
Table YI . shows the average amounts of nitrogen per acre 
per annum, over the eight years, in the rotation, and in the con- 
tinuous crops, respectively : — 
The Nitrogen in the Root-crops. — Without manure, with 
extremely small crops, but very abnormally high percentage of 
nitrogen in them, the amounts per acre were, in the continu- 
ously grown crops only about twice as much as annually comes 
down as combined nitrogen in the rain and minor aqueous de- 
posits from the atmosphere ; whilst, even in the rotation crops, 
the amounts averaged but little more than in the continuous. 
With superphosphate alone, much larger crops, but much 
lower percentages of nitrogen, there was very much more nitro- 
