Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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recipe for degrading soil fertility through continuous cropping. Although
very large farms turned out to mine the soil itself, this was not yet apparent—and
Roman experience in this regard was long forgotten. To the individual
farmer, enclosure was seen as the way to ensure a return on investing
to improve soil fertility from well-manured ground.
Agricultural writers maintained that the key to good crop yields was to
keep an adequate supply of manure on hand—to keep the right ratio of
pasture to field on each farm, or estate as the case increasingly became.
“The Arable-land must be proportioned to the quantity of Dung that is
raised in the Pasture, because proper Manure is the chief Advantage of
Arable-ground.” 5 The key to increasing agricultural productivity was seen
to lie in bringing stock raising and cereal production into proximity and
returning manure to the fields.
Still, not all land was the same; improvements needed to be tailored to
the nature of the soil. British farmland consisted of three basic types:
uplands lying high enough not to flood, lowlands along rivers and wetlands,
and land susceptible to inundation by the sea. These lands had different
vulnerabilities.
On hillslopes, the thin layer of a foot or so of topsoil was essential to
good farming. Such lands were naturally prone to erosion and vulnerable
to poor farming practices. On lowlands, the soil was replenished by upland
erosion that produced fine deposits downslope. “As to Lands lying near
Rivers, the great Improvement of them is their over-flowing, which brings
the Soil of the Uplands upon them, so as that they need no other mending
though constantly mowed.” 6
Working land too hard for too long would reduce soil fertility. Sloping
land was particularly vulnerable. “Where Lands lie upon the sides of
Hills ...great care must be taken not to plow them out of heart.” 7 Recognizing
such connections, most landlords obliged their tenants to fallow
fields every third year, and every other year if manure was unavailable.
Reviving worn-out fields proved highly profitable—when enough land
was enclosed. Under the banner of agricultural improvement, Parliament
repeatedly authorized land enclosures that created large estates at the
expense of common land, enriching the landed gentry and turning peasants
into paupers.
English farmers gradually increased per-acre grain yields to well above
medieval crop yields of twice the seeded amount, which were no greater
than early Egyptian crop yields. Traditionally, historians attributed increased
yields between the Middle Ages and the Industrial Revolution to
let them eat colonies