

WHEAT. 189 



The results on the artificially manured plots show — that Artificial 

 mineral manures alone gave very little increase of produce ; manures - 

 that nitrogenous manures alone gave considerably more than 

 mineral manures alone ; but that mixtures of the two gave 

 very much more than either separately. In two cases the 

 average produce by mixed mineral and nitrogenous manure 

 was more than that by the annual application of farmyard 

 manure ; and in nine out of the twelve cases in which such 

 mixtures were used, the average yield per acre was from 2 to 

 8 bushels more than the average yield of the United King- 

 dom (nearly 28 bushels) under ordinary rotation. 



Such were the results obtained for 40 or 50 years in 

 succession on ordinary arable land ; and that the soil is not 

 a rich one may be judged by the low percentage of nitrogen 

 found in the surface and subsoil. 



As bearing upon the question of the yields of wheat of Nitrogen 

 different soils, and different countries, it will be of interest to ? nd c . < f rbon 

 contrast the condition of soils of very different history in 

 relation to their percentage of nitrogen, and, where prac- 

 ticable, of carbon also. Table 55 (p. 190) shows the characters 

 in these respects — of arable soil under rotation and in fairly 

 good condition; of that of the experimental wheat -field 

 variously manured; of exhausted arable soils, of newly 

 laid-down permanent grass-land, and of old grass-land, at 

 Eothamsted. It also gives results relating to some other old 

 arable soils; to some United States and Canadian prairie 

 soils ; and lastly, to some rich Eussian soils. 



Unfortunately, in the early years of the Eothamsted ex- 

 periments, samples of soil were not taken of a fixed area, 

 and to a fixed depth, so that the results of nitrogen deter- 

 minations in them are not comparable with those taken at 

 later dates to the uniform depth of 9 inches. It is difficult, 

 therefore, accurately to estimate the percentage of nitrogen 

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

 experiments. Some idea may, however, be formed from the 

 results given in the table. Thus, it is seen that in a field 

 which, from 1848 up to the present time, has been under 

 4-course rotation of — roots (fed on the land), barley, legu- 

 minous crop, and wheat, with mineral and nitrogenous 

 manure for the roots commencing each course, the percen- 

 tages of nitrogen in the dry sifted soil were — in 1867 after 

 the fourth crop since manuring (wheat), 0.1402 ; in 1874 

 after the third crop since manuring (clover), 0.1372 per cent ; 

 and in 1883, again after the fourth crop (the wheat), 0.1391 

 per cent. Here, then, under rotation and liberal manuring, 

 and the feeding of the roots on the land, the average per- 

 centage of nitrogen in the surface-soil is maintained at nearly 



