ON RECENT DEVELOPMENTS {N AGRICULTURAL SCIENCE. 273 
seem to show a much greater development of Azotobacter with increased 
powers of fixation in the soil from the Broadbalk than from the Geescroft 
wilderness ; a fact to be correlated with the presence of a fair proportion 
of carbonate of lime in Broadbalk but not in Geescroft field. 
Another example may be drawn from the experiments carried on by 
the late Mr. James Mason at Eynsham Hall, Oxon. He had larje 
cemented tanks filled with burnt clay mixed with appropriate quantities 
of calcium carbonate and phosphate and other nutrient salts, but contain- 
ing no nitrogen. One of these tanks, after inoculation with a trace cf 
ordinary soil, was sown with a mixture of grass-seeds and has carried & 
weak but purely grassy vegetation ever since. According to a recent 
analysis the soil of this tank has in fifteen years accumulated 0:029 per 
cent. of nitrogen in the surface soil and 0-117 per cent. in the second 
layer—equivalent to about 870 and 350 lb. per acre per annum, the 
ratio of carbon to nitrogen in the accumulation being about 18 to 1 and 
12 to 1 respectively. 
Henry has also shown that the shed leaves of many forest trees during 
their decay may bring about the fixation of nitrogen ; and this fact, which 
again depends on the oxidation of the carbohydrates of the leaf to supply the 
necessary energy, has been confirmed in the Rothamsted Laboratory, as 
well as the presence of Azotobacter on the decaying leaf. 
It is obvious that one of the most interesting fields for the study of 
these organisms must lie in the virgin lands of a country like South 
Africa. We all know that virgin soil may on the one hand represent 
land of almost perpetual fertility ; on the other it may constitute wastes of 
any degree of sterility. What are the conditions under which ensues that 
accumulation of humus whose nitrogen will become available under culti- 
vation, the ‘black soils’ famous in every continent? The xcological 
botanists are working out some of the great climatic conditions, the 
amount and distribution of rainfall and temperature which are associated 
with ‘steppe’ areas of great accumulated fertility, but the bacterial flora 
which is fundamentally bound up with the problem remains as yet un- 
explored. 
It is possible also that on some of the newer lands this and kindred 
bacteria are absent because the conditions are not entirely suitable to 
their development. A. Koch has shown that the presence of calcium 
carbonate is necessary to the action of Azotobacter, and determinations of 
the power of soils from the various Rothamsted fields to induce fixation 
confirm his results, the development of the organism in question being 
feeble when the soil was derived from some of the fields that had escaped 
the ‘chalking’ process to which the calcium carbonate of the Rothamsted 
soils is due. 
The value of caicium carbonate in this connection only adds to the 
many actions which are brought about by the presence of lime in the 
soil—-lime, that is, in the form of calcium carbonate, which will behave as 
a base towards the acids produced by bacterial activity. The experi- 
mental fields at Rothamsted afford a singular opportunity of studying the 
action of lime, since the soil, a stiff, flinty loam, almost a clay, is naturally 
devoid of calcium carbonate, though most of the cultivated fields 
contain now from 2 to 5 per cent. in the surface soil, due to the repeated 
applications of chalk, which used to be so integral a part of farming 
practice up to the middle of the nineteenth century. Where this chalk- 
ing process has been omitted, as is the case in one or two fields, the 
1905, T 
