234 



THE ROTHAMSTED EXPERIMENTS. 



amount of nitrogen as well, there was, although the supply 

 of phosphoric acid by manure was exactly the same, now 

 about twice as much of it taken up, as a coincident of the 

 greatly increased growth, due partly to the other mineral 

 constituents at the same time added, but especially to the 

 influence of the increased available supply of nitrogen. 

 Still, only a small proportion of the phosphoric acid applied 

 was taken up, considering the recognised importance of its 

 application for turnips, and its undoubted specific effects on 

 their growth as above described. 

 Rotation Comparing the amounts of phosphoric acid in the rotation 

 uous C cro l T cr0 P s w it n those in the continuous ones, the equally small, 

 or even smaller, amount taken up without manure by the 

 latter, is further confirmation of the incapability of this 

 assumed restorative crop to yield any practical amount of 

 produce without adequate soil supplies. With superphos- 

 phate alone, as also with the mixed manure, the continuous 

 crops took up little more than half as much phosphoric acid 

 as the rotation ones under the assumed fairly parallel con- 

 ditions as to manuring. The deficiency is, however, obviously 

 not due to any deficiency of supply within the soil, but is 

 only a coincident of the less total growth, attributable to a 

 great extent, as has been explained, to the unfavourable 

 mechanical condition of the soil induced by the continuous 

 growth of the crop. 



Lastly, in regard to the phosphoric acid in the turnip 

 crops, it is to be observed that in all cases much more was 

 accumulated in the edible roots than in the leaves which re- 

 main only for manure again ; indeed, in the case of the most 

 normal crops, those grown in rotation with the full mixed 

 manure, there was five or six times as much accumulated in 

 the roots as in the leaves. 



The Phosphoric Acid in the Barley Crops. — Looking first to 

 the amounts in the total produce, grain and straw together, 

 and to the portions of the rotation plots from which the pre- 

 vious root-crops had been removed, it is seen that, without 

 manure, rather more than 13 lb. of phosphoric acid was, on 

 the average, annually removed in the barley crops ; and 

 where superphosphate had previously been applied for the 

 roots, the succeeding barley took up only about 14 lb., that is 

 scarcely any more than without the supply of it ; but where 

 the mixed manure, including nitrogen, had been applied for 

 the roots, there was about one-and-a-half time as much, or 

 rather over 21 lb. of phosphoric acid in the succeeding barley 

 Removal of crops. Then, where the root-crops had not been removed 

 root-crops. f Tom t ^ e i^^ the amounts of phosphoric acid in the suc- 

 ceeding barley crops were, without manure, about 12 lb. per 



Unfavour- 

 able me- 

 chanical 

 condition 

 of soil. 



Phosphoric 

 acid in 

 edible root. 



No man 

 ure. 



With 



superphos- 

 phate. 



Mixed 

 manure. 



