bushels an acre on the fertilized land, and 11.7 bushels where no
plant food was applied. These statements are not mere opinions, but
determined facts whose accuracy stands unquestioned.

On another field at Rothamsted, England, the average yield of barley
for the same sixty years was 43 bushels an acre where nitrogen,
phosphorus and calcium were regularly applied, 42.6 where all five
elements--including potassium and magnesium--were added, but only
14.3 on unfertilized land.

On still another Rothamsted experiment field, where a four-year crop
rotation of turnips, barley, clover (or beans) and wheat has been
practiced since 1848, the yield of turnips in 1908 was 717 pounds an
acre on unfertilized land and 35,168 pounds where the five important
elements of plant food had been regularly applied once every four
years--for the turnips only--since 1848. In 1909 the barley yielded
33.4 bushels an acre on the fertilized land, but only 10 bushels
where no plant food was applied. The yield of clover in 1910 was
8590 pounds an acre on the land fertilized for turnips, but only
1949 on the unfertilized land. The wheat following the clover with
no other fertilizer produced 24.5 bushels an acre in 1911, but 38
bushels where plant food is always applied for turnips grown three
years before.

These are the established facts from the longest accurate record,
and thus the most trustworthy data the world affords; and when one
hears promulgated the very pleasing doctrine that the rotation of
crops will maintain the fertility of the soil it is time to remember
that "to err is human."