and, intelligent attention to these same factors will bring
restoration and high productive power to such lands.

England's Best Lesson in Farming

Where these five elements were supplied regularly to land on the
Rothamsted Experiment Station the average yield of wheat for the
thirty years, 1852 to 1881, was 35.9 bushels an acre, while 13.6 was
the average yield of similar unfertilized land; and during the next
thirty years--1882 to 1911--the corresponding average yields were 38
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."

Fertility in Normal Soils

Of the four important mineral elements, potassium is by far the most
abundant in common soils. Thus, as an average of ten residual soils
from ten different geological formations in the eastern part of
United States, two million pounds of subsurface soil were found to
contain:

Potassium 37,860 pounds
Magnesium 14,080 pounds
Ca