176 



THE ROTHAMSTED EXPERIMENTS. 



The result is exactly similar in the case of the barley ; plot 

 la being manured with ammonium-salts alone, and plot 4a 

 with the same ammonium - salts and mineral manure in 

 addition. 



It is evident that the chlorophyll formation has a close 

 connection with the amount of nitrogen assimilated ; but that 

 the carbon assimilation is not in proportion to the chlorophyll 

 formed if there is not a sufficiency of the necessary mineral 

 constituents available. No doubt there had been as much or 

 more of both nitrogen assimilated, and chlorophyll formed, 

 over a given area, where the mineral as well as the nitro- 

 genous manure had been applied; the lower proportion of 

 both in the dry matter being due to the greater assimilation 

 of carbon, and consequent greater formation of non-nitro- 

 genous substance. 



Effect of 

 unrecov- 

 ered nitro- 

 gen on, suc- 

 ceeding 

 crops. 



Increase 

 from nitro- 

 genous 

 manure. 



The next point to consider is, What is the effect of the 

 unrecovered amount of nitrogen on succeeding crops ? This 

 is illustrated by the results in the coloured columns of Table 

 47 (p. 168). In the table, mineral manure alone is indicated 

 by blue, nitrogenous manure alone by yellow, and a mixture 

 of the two by green. Plot 5 has been manured continu- 

 ously for 43 years with mineral manure alone ; whilst plots 

 17 and 18 each received, alternately, mineral manure, or a 

 quantity of ammonium-salts containing 86 lb. of nitrogen. 

 Thus we are able, for every year, to compare a plot manured 

 with minerals succeeding a previous application of ammo- 

 nium-salts, with a plot receiving mineral manure alone every 

 year. It is seen that, in every case, the application of nitro- 

 genous manure gave a greatly increased yield, frequently 

 doubling that of the plot with mineral manure alone. Again, 

 in every case, the yield of the succeeding year, when the 

 mineral manure followed the previous application of ammo- 

 nium-salts, was reduced approximately to that of the plot 

 continuously treated with minerals alone. A glance down 

 the columns of plots 17 and 18, each coloured alternately 

 blue and yellow, and a comparison of them with the blue 

 column of plot 5, will bring the results strikingly to 

 view. A comparison of the averages of the periods of 8, 

 and of 40 years, of this treatment, clearly shows the essential 

 identity of the results of the continuous and the alternate 

 treatment with mineral manures. The averages for the 40 

 years show an increase in the yield of the mineral manure 

 after ammonia, over the yield of plot 5 with mineral manure 

 alone every year, of only £ of a bushel per acre per annum, 

 in a crop of between 15 and 16 bushels. The non-effect, or 

 the absence, of residual available nitrogen applied in the 



