82 



NITROGENOUS MANURES 



[chap. 



These differences may be illustrated by one of the 

 Rothamsted experiments in 1905, where barley was 

 grown on one plot with 283 lb. of nitrogen in the form 

 of wool dust, on the neighbouring plot with the residue 

 of the same amount of shoddy that had been applied 

 the year before to a Swede crop, and on a third plot 

 with no nitrogen. The results are shown in Table XXI. 



Table XXL— Effect of Excessive Nitrogen on Barley. 

 Rothamsted, 1905. 



This is an extreme case, but it illustrates the effect 

 of an excess of nitrogen in producing a disproportionate 

 amount of straw and a thin, light, nitrogenous barley. 

 Of course some nitrogen is necessary in order to obtain 

 a good-sized berry ; the long series of Rothamsted 

 experiments all show that high quality cannot be 

 secured by merely growing barley on land exhausted 

 of nitrogen : it is the excess, especially the relative 

 excess when the mineral constituents are deficient, 

 that leads to inferior grain. 



Although these results show that the quality, and 

 therefore the composition, of the grain is affected by the 

 amount of nitrogen supplied to the crop, it is really 

 astonishing to find how small are the changes brought 

 about by extreme differences in the manuring. 



To begin with, the plant reacts against variations in 

 the composition of the soil and tends to keep its own 

 composition constant ; when also the time comes for the 



