116 The Rothamsted Barley Experiments. 



course, than for any of the subsequent courses. The table 

 skows that the quantity of barley grown in rotation without 

 manure is very much greater than that grown in succession 

 without manure. Again (omitting the first year), the produce 

 after the removal of the full-manured and larger crops of 

 turnips was uniformly, and on the average, very much higher 

 than after the removed superphosphated turnips, and also 

 generally, and on the average, higher than after the un- 

 manured turnips ; this larger produce of barley, after the 

 removal of the larger crop of turnips grown by the mixed 

 manured, is doubtless due to the fact that there would still 

 be a considerable residue of the manure left within the 

 soil. The results of experiments already discussed have 

 shown that a liberal supply of mineral constituents alone 

 was insufficient to secure a fair crop of barley, but that the 

 further addition of nitrogenous manure raised the produce 

 to a maximum. It may, therefore, be concluded, in the case 

 now under notice, that the larger produce of barley after the 

 full-manured, than after the superphosphated or unmanured 

 crops in rotation, was not attributable to any residue of 

 mineral constituents alone which would remain after the 

 removal of the highly manured roots ; and that the larger 

 produce after the unmanured than after the super- 

 phosphated turnips was not due to a less exhaustion or 

 greater accumulation of available mineral constituents 

 where the smaller crop of turnips was removed. In fact^ 

 as in other experiments, so also in these, in which barley was 

 grown in rotation, and under three very different conditions 

 as to manuring, the evidence is sufficiently conclusive, and 

 therefore corroborative of that in the other cases, that an 

 essential condition for the growth of a full crop of barley, 

 whether in rotation or under less usual conditions, is a liberal 

 supply of available nitrogen within the soil. 



