196 
Nitrification in Acid Sorls. 
By A. D. Hatt, M.A., N. H. J. MILuEr, Ph.D., and C. T. GiMIncHamM. 
(Communicated by H. E. Armstrong, Ph.D., LL.D., F.R.S. Received 
December 19, 1907,—Read February 6, 1908.) 
(From the Lawes Agricultural Trust.) 
Introductory. 
Certain of the permanent grass plots at Rothamsted, which have beem 
cut for hay and have received the same manurial treatment every year 
since 1856,* of late years have declined in yield, and the herbage has. 
assumed an unhealthy condition. The plots affected are those to which 
nitrogen in the form of a mixture of ammonium chloride and sulphate is. 
applied; the one receiving the highest amount of ammonium salts now 
carries a rank vegetation, consisting almost entirely of three species of grass. 
—FHolcus lanatus, Alopecurus pratensis, and <Arrenatherum avenacewm— 
growing in coarse tufts with bare spaces between. The surface of these bare 
patches, which are spreading yearly, consists of a mat of peat-like decayed: 
vegetation ; a similar peaty formation is to be observed on the other plots. 
receiving smaller amounts of ammonium salts. » 
In determining the nitrifying power of a number of Rothamsted soils,t 
My. 8. F. Ashby observed that these grass soils failed to set up nitrification 
when small quantities were added to media suitable to the development. 
of nitrates, indicating the comparative absence of the organisms causing. 
nitrification. It was also noticed that the soil of these plots was distinctly 
acid, sufficiently so to redden blue litmus paper pressed against it in the 
moist state, a condition first observed by Voelckert to be set up by the: 
long-continued uses of ammonium salts on the arable soils of the farm of the: 
Royal Agricultural Society at Woburn. 
Inasmuch as the investigations of Warington and Winogradsky have 
shown that the process of nitrification can only go forward in the*presence 
of a salifiable base and at once stops in an acid medium, it seemed possible 
that the observed decline in fertility of these plots might result from a 
cessation of nitrification due to the acid condition of the soil. 
Though the soil of the grass plots is of the same origin and belongs to 
the same general type as that of the other Rothamsted fields—a stiff loam 
* ‘Phil. Trans.,’ 1900, B, vol. 192, p. 139. 
t ‘Chem. Soc. Trans.,’ 1905, vol. 85, p. 1158. 
t ‘Roy. Agric. Soc. Journ.,’ 1904, vol. 64, p. 355. 
