M.—AGRICULTURE. 267 
always do—and it is now being attacked with much vigour by some of 
the younger scientific workers, particularly in the Californian school : 
Burd, Hoagland, Kelley, Lipman, Stewart, Sharp, and others. There is 
also some valuable work by Gola and other Italians. The natural soil 
solution is not always the best for the growth of plants. It is reasonable 
to suppose that the most efficient method of using fertilisers would be for 
making up the soil solution to the optimum composition and concentration 
for each stage of the growth of the crop. Unfortunately, this cannot yet 
be done. The added fertiliser does not simply increase the concentration 
of the soil solution to the precise extent that might be expected ; there 
are interactions, absorptions, and base exchanges of the kind studied 
first by Way, much later by van Bemmelen and by Gedroiz, and more 
recently by Hissink and by Wiegner. Further, the plant relationships are 
not constant; there is apparently—though this is not certain—more 
response to certain nutrients at one time ofits life than at another. A great 
advance in crop production may be expected when the soil chemists have 
discovered the laws governing the soil solution, when the plant physiologists 
can give definite expression to the plant’s response to nutrients, and when 
someone is able to put these results together and show how to alter the soil 
solution so that it may produce the maximum effect on the plant at the 
particular time. The new soil chemistry will yet have its triumphs. 
The Soil Micro-organisms : Can they be Controlled ? 
It is now more than forty years since the discovery of the great impor- 
tance of micro-organisms in determining soil fertility. Practical applications 
necessarily lag far behind; but already three have been made, each of 
which opens out great possibilities for the future. The long-standing 
problem of inoculation of leguminous crops’ with their appropriate organ- 
isms has already been solved in one or two of its simple cases, chiefly lucerne 
on new land, and the new process has helped in the remarkable extension 
of the lucerne crop in the United States and in Denmark. We believe at 
Rothamsted that the mage difficult English problem is now solved also. 
Interesting possibilities are opened up by the observation that a prelimi- 
nary crop of Bokhara clover seems to facilitate the growth of the lucerne. 
The organisms effecting decomposition are now coming under control, 
and are being made to convert straw into farmyard manure (or a material 
very much like it) without the use of a single farm animal. The process 
was worked out at Rothamsted, and is being developed by the Adco 
Syndicate, who are now operating it on a large scale and are already 
successfully converting some thousands of tons of straw annually into 
good manure. 
The third direction in which control of the soil organisms is being 
attempted is by partial sterilisation. This process is much used in the 
glasshouse industry in England, and it has led to considerable increases 
in crop yields. The older method was to use heat as the partial sterilising 
agent, and this still remains the most effective, but owing to its costliness 
efforts have been made to replace it by chemicals. Considerable success 
has been attained ; we have now found a number of substances which seem 
promising. Some of these are by-products of coal industries; others, 
such as chlor- and nitro-derivatives of benzene or cresol, are producible as 
crude intermediates in the dye industry. 
