though that was because we persisted in shooting nitrates into the air.
The area producing wheat was by decades:[1]

THE WHEAT FIELDS OF THE WORLD

Acres

1881-90 192,000,000
1890-1900 211,000,000
1900-10 242,000,000
Probable limit 300,000,000

If 300,000,000 acres can be brought under cultivation for wheat and the
average yield raised to twenty bushels to the acre, that will give
enough to feed a billion people if they eat six bushels a year as do the
English. 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