"About 150 per cent. of it," Percy replied.

"One hundred and fifty per cent! Why, you can't have more than a
hundred per cent. of anything."

"Oh, yes, you can. The twenty-four bushels are one hundred per cent.
of what the fertilizers produced, and the land itself increased this
by fifty per cent., so that the fertilized land produced one hundred
and fifty per cent. of the increase from the plant food applied.

"Well, that's too much college mathematics for me; but do you mean
to say that it would take the whole thirty-seven bushels to pay for
the plant food that produced the increase of twenty-four bushels?"

"That is exactly what I mean. I see that you do not like percentage
any better than I do. Really the acre is the best agricultural unit.
We buy and sell the land itself by the acre; we report crop yields
at so many bushels or tons per acre; we apply manure at so many
loads or tons per acre; we apply so many hundred pounds of
fertilizer per acre; sow our wheat and oats at so many pecks or
bushels per acre; and we ought to know the invoice of plant food in
the plowed soil of an acre and the amounts carried off in the crops
removed from an acre.

"Now, referring again to these figures from the forty acres of
clover at two tons per acre. If the eighty tons were burned and the
ashes mixed with the surface soil on a tenth of an acre the increase
per acre would be as follows: