No weeds choke
the wheat plants or rob them of their food; but that field does not
produce as much wheat by 30 bushels per acre as the _season_ is capable
of producing. Why? The answer is evident. _Because the wheat plants do
not find food enough in the soil._ Now, anything that will furnish this
food, anything that will cause that field to produce what the climate or
season is capable of producing, is manure. A gardener may increase his
crops by artificial heat, or by an increased supply of water, but this
is not manure. The effect is due to improved climatic conditions. It has
nothing to do with the question of manure. We often read in the
agricultural papers about '_shade_ as manure.' We might just as well
talk about _sunlight_ as 'manure.' The effects observed should be
referred to modifications of the climate or season; and so in regard to
mulching. A good mulch may often produce a larger increase of growth
than an application of manure. But mulch, proper, is not manure. It is
climate. It checks evaporation of moisture from the soil. We might as
well speak of rain as manure as to call a mulch manure. In fact, an
ordinary shower in summer is little more than a mulch. It does not reach
the roots of plants; and yet we see the effect of the shower immediately
in the increased vigor of the plants. They are full of sap, and the
drooping leaves look refreshed. We say the rain has revived them, and so
it has; but probably not a particle of the rain has entered into the
circulation of the plant. The rain checked evaporation from the soil and
from the leaves. A cool night refreshes the plants, and fills the leaves
with sap, precisely in the same way. All these fertilizing effects,
however, belong to climate. It is inaccurate to associate either
mulching, sunshine, shade, heat, dews, or rain, with the question of
manure, though the effect may in certain circumstances be precisely the
same."

Charley evidently thought I was wandering from the point. "You think,
then," said he, "manure is _plant-food that the soil needs?_"

"Yes," said I, "that is a very good definition--very good, indeed,
though not absolutely accurate, because manure is manure, whether a
particular soil needs it or not." Unobserved by us, the Deacon and the
Doctor had been listening to our talk. --"I would like," said the
Deacon, "to hear you give a better definition than Charley has given."
--"Manure," said I, "is anything containing an element or elements