224 THE EOTHAMSTED EXPERIMENTS. 



was considerably less in the continuous than in the rotation 

 crops. 



So far as the unmanured and the superphosphate crops 

 are concerned, it is obvious that the growth year after year 

 must be much more exhausting, both of nitrogen and of 

 certain essential mineral constituents, in a condition of com- 

 position and of distribution within the soil and subsoil avail- 

 able to one particular crop, than when the crop is grown in 

 alternation with others, of different requirements, habits, and 

 root-ranges. 



It has been explained that in the case of the mixed manure 

 rotation plots there was applied for the first crop of the 

 course, besides a full supply of mineral constituents, about 

 140 lb. of nitrogen ; at the average rate, therefore, of 35 lb. 

 per acre per annum over the four years. But, in the case of 

 the continuously grown wheat crops, not only a full supply of 

 • mineral manure, but 43 lb. of nitrogen as ammonium-salts, 

 was 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 application of the manure 

 for the roots, there was more nitrogen, and more of other con- 

 stituents also, in a condition of composition and of distribu- 

 tion 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 ex- 

 perimental 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 assump- 

 tion, 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 re- 

 tained. 

 Dry matter Comparing the amounts of dry matter accumulated in the 

 ^wTfaitoxo different rotation crops, and taking as the most normal the 

 crops. 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 approxi- 

 mately equal amounts ; and each considerably more than 

 either of the fallow crops — the roots or the Leguminosae. 



