18 



Mr. A. D. Hall and Dr. N. H. J. Miller. [Mar. 30, 



of the determinations. In the Broadbalk Field, Plot 10 can be compared with 

 Plot 7 ; both receive the same amount of ammonium salts, but Plot 7 receives 

 the minerals in addition. The rate of loss is practically identical, 1010 lbs. per 

 acre per annum on Plot 7 and 1045 lbs. on Plot 10. Unfortunately Plot 5, 

 receiving minerals only without nitrogen, cannot be compared with the 

 unmanured Plot 3, because both Plots 5 and 6 show an entirely exceptional 

 rate of loss, not to be accounted for unless it be that one of the dells, from 

 which the field was originally chalked, lies in these two plots, and may have 

 caused a very irregular distribution of the chalk. But if the rate of loss on 

 Plot 5 be calculated over the period 1881 — 1904 only, it amounts to 880 lbs. 

 per acre against 800 lbs. per acre on the unmanured plot. 



In the Hoos Pield the results are too irregular to bear much discussion, 

 for the plots which receive minerals — 4o, 4a, 4n — start with less than half 

 the chalk contained by the corresponding lo, 1a, and In. 



In the plots, however, which receive ammonium salts as a manure, the loss 

 of calcium carbonate is much increased. A reaction of the type 



(NH 4 ) 2 S0 4 + CaC0 3 = (NHOaCOa + CaSO* 



takes place as soon as the ammonium salts are dissolved, the ammonium 

 carbonate is adsorbed by the surface action of the humus and the finer clay 

 particles of the soil until it is nitrified, while the calcium sulphate passes 

 forthwith into the drainage water. When heavy rain follows the application of 

 the ammonium salts to the Broadbalk wheatfield, only traces of ammonia find 

 their way into the drains, whereas there is an immediate great increase in 

 the calcium sulphate and chloride present in the drainage water. At 

 Eothamsted the manure termed ammonium salts consists of an equal mixture 

 of ammonium sulphate and chloride, and is applied to the various plots at the 

 rate of 200, 400, and 600 lbs. per acre, quantities which would react with 

 161, 321, and 482 lbs. respectively of calcium carbonate. Before, how- 

 ever, the ammonium carbonate thus produced has been long in the soil a 

 second molecule of calcium carbonate must be consumed to provide a base for 

 the nitrous and nitric acids formed by its nitrification. This would make 

 the loss caused by the application of 200 lbs. of ammonium salts up to 

 321 lbs. of calcium carbonate, half of which is caused by the initial reaction 

 producing ammonium carbonate, and half by the nitrification of the latter. 

 In order to determine the rate of loss in the field, it will be convenient, in 

 the various cases where a comparison is possible, to subtract the average 

 rate of loss on a plot without ammonium salts from the plots receiving 

 ammonium salts, and divide by 2 or 3, as need be, to find the effect in each 

 case of 200 lbs. of ammonium salts. 



