"Do you think this land could be made as valuable as the Illinois
land just by a liberal use of limestone and legumes?" asked
Adelaide.

"I should have some doubt about that," Percy replied. "Your very
level uplands that neither lose nor receive material from surface
washing are very deficient in phosphorus and much poorer than ours
in potassium and magnesium; and your undulating and steeply sloping
lands are more or less broken, with many rock outcrops on the points
and some impassable gullies, which as a rule compel the cultivation
of the land in small irregular fields. A three-cornered field of
from two to fifteen acres can never have quite the same value per
acre as the land where forty or eighty acres of corn can be grown in
a body with no necessity of omitting a single hill. Then there is
some unavoidable loss from surface washing, so that to maintain the
supply of organic matter and nitrogen will require a larger use of
legumes than on level land of equal richness. In addition to this is
the initial difference in humus content. This is well measured by
the nitrogen content. While your soil contains eight hundred pounds
of nitrogen on the steeper slopes and one thousand pounds on the
more gently undulating areas, ours contains five thousand pounds in
the brown silt loam and eight thousand pounds in the heavier black
clay loam. This means that our Illinois prairie soil contains from
five to ten times as much humus, or organic matter, as your best
upland soil. To supply this difference in humus would require the
addition of from four hundred to eight hundred tons per acre of
average farm manure, or the plowing under of one hundred to two
hundred tons of air-dry clover. This represents the great reserve of
the Illinois prairie soils above the total supplies remaining in
your soils.