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Whether this maximum is correct or not there is evidently some
limit to the area which has suitable soil and climate for growing wheat,
so we are ultimately thrown back upon Crookes's solution of the problem;
that is, we must increase the yield per acre and this can only be done
by the use of fertilizers and especially by the fixation of atmospheric
nitrogen. Crookes estimated the average yield of wheat at 12.7 bushels
to the acre, which is more than it is in the new lands of the United
States, Australia and Russia, but less than in Europe, where the soil is
well fed. What can be done to increase the yield may be seen from these
figures:
GAIN IN THE YIELD OF WHEAT IN BUSHELS PER ACRE
1889-90 1913
Germany 19 35
Belgium 30 35
France 17 20
United Kingdom 28 32
United States 12 15
The greatest gain was made in Germany and we see a reason for it in the
fact that the German importation of Chilean saltpeter was 55,000 tons in
1880 and 747,000 tons in 1913.


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