102 EXPERIMENTS UPON ROOT-CKOPS 



neither nitrate of soda nor ammonium -salts leave any effective 

 residue. 



In seasons of exceptional growth, with a big crop like that 

 of 1900, it might be expected that as the plant was utilising 

 much more thoroughly the supply of nitrogen, then the smaller 

 amounts on some of the plots, plentiful enough for an ordinary 

 year, might prove to be insufficient. There is no indication, how- 

 ever, of this being the case, as may be seen by a consideration of 

 Table XLI. ; the increase of crop on Plots 4, receiving no dung 

 but a complete mineral manure, continues with each application 

 of nitrogen, but not more so than in normal seasons. On the 

 dunged plots, indeed, it is not those receiving most nitrogen 

 (Plots 1 and 2 AC) which give the highest crop, but those 

 cross-dressed with nitrate of soda, as though the availability of 

 the nitrogen and the presence of a large supply of alkaline salts 

 had been the determining factors in producing the maximum 

 crop. The whole results go to show that, dependent on 

 nitrogen as the mangold crop is, the first application is the 

 most effective, each succeeding addition of nitrogen producing 

 a smaller return in the shape of an increase of crop. 



The injurious effects of the very large amounts of nitrogen 

 added to some of the plots is very manifest wherever there is 

 more nitrogen than the plant can properly deal with. The 

 leaves have a dark green appearance, are much curled and 

 crinkled, and show an increased tendency to variegation, the 

 chlorophyll collecting into dark green or almost black blotches 

 on the lighter background of the leaf. The leaf- stalks are 

 often much more coloured, and become a bright orange 

 yellow. 



On these plots the leaves do not ripen off and obtain the 

 general yellow flaccid appearance presented on the more 

 healthy plots when the crop is ready to lift ; instead, the outer 

 leaves begin to die and shrivel up quite early in October ; 

 in some places they show numbers of dead spots and burnt- 

 looking patches round the edges of the leaf. 



The destruction appears to be due to a leaf-spot fungus, 



