12 



Next, it is to be observed that the wheat plant on plot loa, manured 

 with ammonium-salts alone, shows a much higher percentage of nitrogen 

 than that of plot 7, with the same amount of ammonium-salts, but with 

 mineral manure in addition. The high proportion of chlorophyl again 

 goes with the high nitrogen percentage; but the last column of the table 

 shows that on plot loa, with ammonium-salts without mineral manure, 

 with the high percentage of nitrogen and high proportion of chlorophyl 

 in the green produce, there was eventually a very much less assimilation 

 of carbon. The result is exactly similar in the case of the barley ; 

 plot i a being manured with ammonium-salts alone, and plot 42. with the 

 same ammonium-salts and mineral manure in addition. 



It is evident that the chlorophyl formation has a close connection 

 with the amount of nitrogen assimilated; but that the carbon assimila- 

 tion is not in proportion to the chlorophyl 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 

 chlorophyl formed, over a given area, where the mineral as well as the 

 nitrogenous 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-nitrogenous substance. 



The next point to consider is, what is the effect of the unrecovered 

 amount of nitrogen on succeeding crops. This is illustrated Dy the 

 results in the colored columns of Table I. ,In the table mineral manure is 

 indicated by blue, nitrogen as ammonium-salts by yellow, and a mixture 

 of the two by green. Plot 5 has been manured continuously for thirty- 

 two years with mineral manure alone; whilst plots 17 and 18 each 

 received mineral manure, and a quantity of ammonium-salts containing 

 86 Ibs. of nitrogen alternately. Thus we are able, for every year, to 

 compare a plot manured with minerals, succeeding a previous applica- 

 tion of ammonium-salts, with a plot receiving mineral manure alone 

 yearly. It is seen that, in every case, the application of nitrogen 

 has given a greatly increased yield, frequently doubling that of the plot 

 with mineral manure alone. Again, in every case, the yield of the suc- 

 ceeding year, when the mineral manure was applied, was reduced ap- 

 proximately to that of the plot continuously treated with minerals alone. 

 A glance down the alternately blue and yellow columns of plots 1 7 and 

 1 8, and a comparison with the blue column of plot 5, will bring these 

 results strikingly to view. A comparison of the averages of the periods 

 of four, eight, sixteen, and thirty-two 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 thirty- 

 two years show an increase in the yield of the mineral-manure years 

 after ammonia, over the yield of plot 5, of only ^ of a bushel per acre 

 per annum in a crop of between fifteen and sixteen bushels. The non- 

 effect, or the absence, of residual nitrogen applied in the form of ammo- 

 nium-salts, is evident. In other words, nitrogen as ammonium-salts 

 applied in any one year is practically exhausted that year, in the crop or 

 otherwise, leaving practically none for subsequent action. 



Again, plot 16, for thirteen years, from 1852 to 1864 inclusive, re- 

 ceived annually mixed mineral manure and ammonium-salts, containing 

 a double quantity (172 Ibs.) of nitrogen ; and since that time, for nineteen 

 years (1864-1883), it has been left unmanured. During the thirteen 

 years of heavy manuring there was a large yield, in two cases exceeding 



