This is a fascinating
book about soil and soil degradation, especially soil erosion, and how it has
affected societies, ancient and modern. Montgomery, a geologist, speaks of the
twin problems of soil degradation and soil erosion. He believes these problems
are solvable and deserve more attention since not solving them can have severe
future consequences. He notes that he was strongly influenced by an old
out-of-print book he found as a bargain in a bookstore called Topsoil and
Civilization, by two soil conservation scientists in the 1950s. Montgomery
specialized in geomorphology, so erosion and sedimentation are two of the main
processes he studies. He came to realize that humans contribute to these
processes much more than people tend to realize. He notes that archaeologists
have documented soil erosion as a major cause of the decline or collapse of
ancient societies worldwide. He notes that he was taught that it was mainly
deforestation that caused soil loss but he came to realize that agriculture was
a much bigger culprit. He discovered that flat agricultural lands, due to
agriculture, were eroding as fast as steep slopes. He explains that when soil
is eroded faster than it is produced, there is soil loss. He notes:
“The estimated rate of world soil erosion now exceeds
soil production by as much as 23 billion tons per year, an annual loss of not
quite one percent of the world’s agricultural soil inventory.”
He concedes that our ingenuity will allow us to preserve
more soil as time passes and as the effects become more pronounced. He mentions
the idea of ‘peak soil’ or when we had the most available soil. That was
sometime before the advent of agriculture. Like it or not we need to reform
agriculture in a way that optimizes soil preservation and minimizes soil
erosion.
Soil, at least
the upper part, is alive with microorganisms. He notes that some of the
earliest books were agricultural manuals that included information about soils.
He notes that soil erosion happens slowly enough that it is hardly noticed so
it does not seem as bad as it really is. Crop breeding and chemical fertilizers
have allowed four crops: wheat, rice, maize, and barley to become the dominant
food crops. He says that farmers, politicians, and environmental historians
speak of “soil exhaustion,” which refers to loss of soil fertility through time
and also may be applicable to soil erosion. He notes:
“Soil is an intergeneration resource, natural capital
that can be used conservatively or squandered.”
He notes that the
history of ancient civilizations is one of initial fertile soil and later
abandonment when the soil becomes too unfertile and often eroded away. That
is why, he says, societies such as the Greeks, Romans, and Mayans all lasted
about a thousand years.
“Although historians are prone to credit the end of
civilizations to discrete events like climate changes, wars, or natural
disasters, the effects of soil erosion on ancient societies were profound”
He talks about
Charles Darwin’s last book, which was about worms and how they make soil. Darwin
concluded that worm castings, or excrement, was how worms made soil. He also
noted the rate of soil formation in his English countryside. By constantly weighing
worm castings he concluded that worms contributed to making about one-tenth to
one-quarter inch of soil per year. He also found that burrowing worms also
move significant amounts of soil. He basically discovered that worms plow the
soil, over time.
He notes that the
oldest soil, mineral soil from weathered exposed rock, is more than three
billion years old. The minerals weathered to clays. These fossil soils are
clays rich in potassium since there were no plants to remove it. Later, heat-loving
bacteria produced soil below the bacterial mats on the rock substrate. Once
plants evolved the rate of soil formation skyrocketed as plant roots held soil
and rock fragments together and assisted reactions that increased mineral weathering
rates. Microorganisms also assist those reactions and soil formation. Soil
microorganisms are highly variable and there are so many that we have yet to
discover them all.
Many physical and chemical processes help the soil to form, including burrowing animals and insects, roots that hold soil together
and pry open rock, falling trees that bring rocks closer to the surface, and
the breakdown of rocks into fragments and eventually into mineral grains. Soil
is often classified into grain sizes, basically clay, silt, and sand. Silt is
best because it doesn’t drain water too fast like sand or dry out like clay.
Ideally, a mix of clay, silt, and sand, known as loam, is the best soil for growing
plants. Some plants, or rather the bacteria on their roots, can “fix” nitrogen,
which means they can pull nitrogen from the air and use it to fertilize growth.
Clover is one example. In 1941 UC Berkeley professor Hans Jenny identified five
factors governing soil formation: parent material (rocks), climate, organisms,
topography, and time. There is great variation in soil types often due to
differences in parent material but also due to differences in the other
factors. Soils are thinner on slopes and thicker in valleys. High rainfall
rates and warm humid environments increase rates of chemical weathering and
soil formation. Tropical soils tend to get leached of nutrients.
Soil erosion
rates also depend on parent material, topography, and climate. Higher organic content
leads to better soil binding and decreased erodibility. Steep slopes erode
faster. Plowing causes increased soil erosion, especially on steeper slopes.
Rain makes small channels called rills and larger channels called gullies, both
of which can be readily seen in most areas. High rainfall rates lead to more
erosion.
Soil horizons from
top to bottom consist of the O horizon which is the loose partially decomposed
leaf, twig, and other plant matter, the A horizon which is the nutrient-rich
decomposed organic matter we call topsoil, and the B horizons which are thicker
but less fertile. The B horizons are higher in clay, have lower pH, and may
have hardpan layers, all of which qare less fertile for plants.
“Globally, temperate grassland soils are the most
important to agriculture because they are incredibly fertile, with thick,
organic-rich A horizons. Deep and readily tilled, these soils underlie the great
grain-producing regions of the world.”
Plowing exposes
soil to oxidation and allows it to be readily eroded when it rains. Thus. Conventional
agriculture that utilizes plowing is responsible for much of the concerning soil
erosion around the world. More plowing means more erosion. The USDA estimates that
on average it takes five hundred years to make an inch of topsoil.
“But agricultural practices can also retard erosion.
Terracing steep fields can reduce soil erosion by 80 to 90 percent by turning
slopes into a series of relatively flat surfaces separated by reinforced steps.
No-till methods minimize direct disturbance of the soil. Leaving crop residue
at the ground surface instead of plowing it under acts as mulch. Helping to
retain moisture and retard erosion. Interplanting crops can provide more
complete ground cover and retard erosion.”
Rates of soil
erosion vary by year and can be difficult to predict. The more direct measurements
we get over time for each area the more we will know. Even less is known about
the rates of soil formation for different areas.
Agriculture
developed independently in Mesopotamia, northern China, and Mesoamerica. Montgomery
recounts several ideas about the development of agriculture, noting that increasing
population density explains the origin and spread of agriculture. The presence
of large-seeded cereal grains like wild wheat and barley in the Middle East made
them easy to convert to cultivation. He recounts animal domestication as well.
“Not long after the first communities settled into an
agricultural lifestyle, the impact of top-soil erosion and degraded soil fertility
- caused by intensive agriculture and goat grazing - began to undermine crop
yields. As a direct result, around 6000 BC whole villages in central Jordan
were abandoned.”
Irrigation became
common along the Tigris and Euphrates Rivers where canals were dug to water fields.
The soil was very fertile, but the rainfall amounts were low. By 4500 BC all
the fertile land in Mesopotamia was under cultivation. That is about when the
plow appeared, he notes. Around 3000 BC another problem became apparent.
“Groundwater in semiarid regions usually contains a lot
of dissolved salt. Here the water table is near the ground surface, as it is in
river valleys and deltas, capillary action moves groundwater up into the soil
to evaporate, leaving salt behind in the ground.”
The buildup of salt poisons and stunts the growth of crops. Wheat
is especially sensitive to soil salinization. As a result, by 2500 BC the amount
of wheat grown dropped and the amount of barley grown increased. By 2000 BC
wheat no longer grew in Mesopotamia. White layers of accumulated salt reached
the soil surface by then. Through time the salinization spread northward
leading to a collapse of agriculture in Central Mesopotamia between 1300 – 900 BC.
Egyptian agriculture
along the Nile River was an exception in that the annual flooding of the river spread
silt and humus along the floodplain and essentially re-fertilized the soil. Water
was directed to where it was needed by canals and overflow channels. After the
annual flooding, the water dropped to about 10 feet below the surface, so salinization
was never an issue, at least until the nineteenth century when irrigation was
increased to grow cotton for export to Europe. The building of the Aswan dam in
1964 by Soviet engineers changed the dynamics of the Nile flooding and drastically
lowered the flow of silt and humus to the agricultural region. Now, Egypt
imports most of its food.
“Although the dam allows farmers to grow two or three
crops a year using artificial irrigation, the water now delivers salt instead
of silt. A decade ago salinization had already reduced crop yield from a tenth
of the fields on the Nile delta. Taming the Nile disrupted the most stable agricultural
environment on Earth.”
The Yao Dynasty in
China (2357-2261 BC) surveyed and classified soils into nine types. By 500 BC the
Chinese developed a soil classification system based on color, texture,
moisture, and fertility. The earliest farmers along the commonly flooding Yellow
River cultivated terraced slopes above the valley, moving down to the floodplain
later when the population increased. Levees were built to contain water. These had
to be built higher and higher as silt accumulated in them so that the riverbed
climbed above the alluvial plain at a rate of about a foot per century,
reaching 30ft above it by the 1920s. This guaranteed that any flooding would be
devastating. Millions drowned or starved due to crop losses.
Montgomery tells
the story of Walter Loudermilk, a forester and scholar who began working on famine
prevention in China in 1922. Loudermilk figured out how soil erosion has affected
Chinese society through time. He later studied soil erosion around the world. In
China, he concluded that farming steep slopes was responsible for much soil
erosion, as it was in other places. Plowed slopes erode much faster than plowed
flat valleys. Plowing followed by overgrazing can be a deadly combination for guaranteeing
soil erosion.
Hesiod in the 8th
century BC was the first to write about agriculture in ancient Greece, which
was mainly subsistence agriculture. Xenophon, in the 4th century BC, noted the practices
of adding manure and burned crop stubble back into the soil. Ancient Greece had
thin poor rocky soil that could not support many crops. Soil erosion added to
the difficulties, with Plato and Aristotle both noting that the agriculture of
previous centuries degraded the soil. However, it was not until plowing became
common that soil erosion increased beyond soil production. Fertil valleys were
cultivated until more land was needed and farmers moved to cultivate slopes,
a story repeated in many places around the world. The southern Argolid uplands
lost about 15 inches of soil due to Bronze Age agriculture, with some lowland
slopes losing up to three feet. Hesiod, Homer, and Xenophon mentioned the
two-field systems with alternate fallow years. Fields, including the fallow
ones, were plowed three times a year. By later classical times, terrace farming
was the norm to try and keep soil from eroding off of slopes.
The soil from the
slopes ends up filling streams and floodplains with sediment. The Romans
utilized careful manure spreading and planting overstory and understory crops
to outcompete weeds. Silt eroded from hills clogged the Tiber River and led to
marshy valleys that could not be cultivated. Rome and Carthage had agricultural
manuals, helping them grow olives, grapes, figs, grains, and other crops. The Roman writer Varro noted that farmer’s fields
were being converted to grazing pastures so much that food had to be imported. The
Romans knew the importance of crop rotation, leaving fields fallow for some seasons,
growing legumes (for their nitrogen-fixing effects), and growing native cover
crops. They also applied crushed marl, a limestone, to fields. Sediments in
lakes and positions of ancient buildings and artifices above the current ground
show that the soil was heavily eroded over time. Erosion rates of a fraction of
an inch per year can add up to several feet over centuries. Sedimentation in
the valleys is also apparent as the sediment filled in coastal areas, once
under water. Some ports are now miles inland from the coast due to the
sedimentation. The Romans famously salted the Carthaginian lands as punishment in
146 BC, which recovered in a few years. They also translated Carthaginian agriculture
manuals. Under Roman occupation, that part of North Africa became a great olive-growing
area for export. However, soil erosion took its toll a few hundred years later there
as well. Soil erosion and exhaustion were also implicated in the downfall of
the Roman Empire. The farmers were indebted due to poor yields. This was the
model that led to Medieval serfdom.
In 1864 George
Perkins March wrote Man and Nature after his world travels which described the degrading
of agricultural land. Later Walter Lowdermilk would document the problem all
over the world, especially in the Middle East. The story was the same: eroded
hills and sediment-filled valleys burying ancient cities. He noted the terraces
of Lebanon. Building terraces is labor-intensive and prevents soil erosion as
long as they are not neglected. Logging out of the cedar forests for export to Egypt
and Mesopotamia led to increased erosion. Grazing replaced slope agriculture
once the soil was eroded and often prevented the original vegetation from
growing back and gradually producing soil again.
The Mayans
excelled at agriculture, but they too fell to population growth and subsequent soil
degradation. They grew maize, which was first domesticated around 2000 BC. Soil
erosion was at a peak when the society began to severely decline. They practiced
slash-and-burn agriculture. They had to farm thin easily eroded soil and since
they did not practice animal agriculture, they did not have manure. Slash-and-burn
worked great until the population rose enough to accelerate soil erosion and
loss of fertility. As in many other areas, the soil was of the lowest quality where
it had been cultivated the longest. There was evidence, as in many other places,
that as the population grew more slopes were cultivated, accelerating the erosion of
the soil. The stories are similar in Central America and the American
Southwest.
Montgomery shows that
there were some exceptions to the rule of soil erosion. One was the Colac
Valley area in Peru where farmers utilized terracing, intercropping, crop rotations
that included legumes, fallowing, and the use of manure, and ash. The farmers
did not plow but planted directly into the ground with a chisel-like device. These
soils are currently in good shape and highly fertile.
He gives a model
of agricultural development here wealth increases the land’s capacity to support
people and allows the population to expand to use the available land. Once the
soil erodes the marginal land the population contracts rapidly.
“This roller-coaster cycle characterizes the relation between
population and food production in many cultures and contexts because the
agricultural potential of the land is not a constant. Both technology and the
state of the soil influence food production.”
Soil health is vital to determining how many people an
amount of land can support. Pollen preserved in lake beds shows how farming
spread in Europe. Large amounts of charcoal and increases in sedimentation
correlate with the beginning of cereal grain pollen in each area.
“Put simply, European prehistory involved the gradual
migration of agricultural peoples, followed by accelerated soil erosion, and a
subsequent period of low population density before either Roman or modern times.
Just as in Greece and Rome, the story of Central and Western Europe is one of
early clearing and farming that caused major erosion before the population
declined, and eventually rebounded.”
The introduction
of alfalfa and clover helped European soils recover fertility. Hay fields
became common in the sixteenth and seventeenth centuries. The cattle and sheep
that ate the hay also manured the fields.
John Fitzherbert’s
Book of Surveying from 1523 was the first work on agriculture in English.
Early farming models of three acres and a cow evolved into tenant farming on
large estates. The Dutch began mixing manure, leaves, and other organic waste
into the soil. The Danes also improved their soil through crop rotations, legumes,
and manure. The Flemish practiced winter cropping of clover and turnips for
fodder and ground cover. Land improvers, sometimes known as yeomen, experimented
with soil additives and draining fields, Recipes for additives, fallowing, and crop
rotations were developed to optimize productivity.
The Irish began
growing potatoes to feed their people but grew many other crops and meat for
export, most to Britain by 1800. By then Ireland was run as an agricultural
colony for Britain. Even during the peak of the famine of 1846 most of their food
was exported. Peasant farmers suffered. People fled. One of my own relatives
came to America from Ireland as a child during the famine years. Soviet peasants
starved while exporting their food to cities. By 1900 many European nations
depended on imported food. As more marginal land was brought into production,
crop yields dropped.
By midcentury plantations
for things like bananas, coffee, and sugar cane were established to supply the
world. The soil in Guatemala where coffee and bananas were grown on slopes was
degrading fast. In 1998 Hurricane Mitch dumped a year’s worth of rain on the
country and landslides and flooding killed more than ten thousand people. Farming
made the problem much worse. Farms that practiced soil conservation fared the best
and showed the importance of conservation practices.
In the U.S. and
in the Amazon, the soils were different, but the cycle was similar:
“The modern cycle of forest clearing, peasant farming, and
cattle ranching strips off topsoil and nearly destroys the capacity to recover
soil fertility. The result is that the land sustains fewer people. When they
run out of productive soil, they move one.”
Tobacco farmed in
Maryland, Virginia, and the Carolinas was a profitable export, but the crop
was also a very heavy feeder that depleted soil fertility. A farmer could only
depend on three or four tobacco crops on a piece of land before the soil as
depleted and partially eroded. At the time there was plenty of land, so the
trend was to keep moving the farms as the soil fertility was depleted. Soil
improvement, or soil husbandry, was practiced by some farmers. Ben Franklin and
George Washington were interested in it. Washington used marl (crushed limestone),
gypsum, and manure as fertilizers and plowed in crops of peas, grasses, and buckwheat.
He collected manure in barns to spread and planted cover crops. In the late
1700s contour plowing, or plowing along contours, on slopes began as new plow
designs were adopted. This helped to reduce erosion, but it was a lot of work
so not that popular. The growing of cotton in the South of the U.S. was a similar
story to tobacco where land was depleted, and farms migrated to new lands. German
and Dutch farmers who emigrated to Pennsylvania brought their farming practices
with them. Farmers began to realize that all soils are different. Some are too
acidic and adding limestone raises the pH. The soil then reacts positively to manure and fertility increases. Early geologist Charles Lyell toured the U.S. South in
the 1840s and drew the following illustration of a deep gully formed as a result
of recently cleared fields in 1846. The gully began to form in the 1820s and
when he drew it, it was fifty feet deep, two hundred feet wide, and three
hundred yards long. Lyell traveled the rivers by canoe and remarked on the dramatic
effects of soil erosion.
Montgomery notes
the main issues in the South:
“The immediate causes of soil exhaustion in the antebellum
South were not mysterious. Foremost among these were continuous planting
without crop rotation, inadequate provision for livestock to provide manure, and
improvident tilling straight up and down sloping hillsides that left bare soil
exposed to rainfall. But there were underlying social causes that drove these
destructive practices.”
Those causes included a tenant farming system that did not
encourage soil conservation and slavery. Tobacco and cotton monoculture
cropping required slave labor to make a profit. Forced labor and absentee
landlords do not favor soil conservation.
Seaports along
estuaries on the Atlantic Coast were turned into mud flats after 50 years of
upland farming. Northern areas were protected from erosion in the winter by snow
and frozen ground, but the intense rains of the South eroded bare land quickly
and thoroughly as the deep gulleys show.
“Sheet-wash erosion is so slow and gradual that some
farmers fail to recognize it and believe that their soils have deteriorated through
exhaustion of the fertility, whereas they have slowly and almost imperceptibly
worn away to the subsoil.”
He notes that archaeologists
recently discovered soil in the Amazon, now known as terra preta that
was black and very fertile, a rarity in the tropics. It had been cultivated for
many years as the presence of settlements showed. The soil had been amended with
pottery shards, organic matter, bones, fish, human and animal waste, trash, and
charcoal. The oldest layers were 2000 years old. Some researchers think the
Amazonians brought some of the terra preta to “inoculate” new areas. The site
was occupied from about 360 BC to about 1440 CE. The current slash-and-burn agriculture
of Brazil’s Amazon region is likely a newer model dependent on the ability to remove
large trees with advanced tools. Before that, the area was an agroforestry
project with understory plantings. Jungle areas in Thailand show similar soil-improved
areas around settlements.
The fertile loess
soils in the U.S. Midcontinent areas from Western Ohio to Iowa and Missouri
were blown off by the high winds coming off the ice sheets to the north. Glaciers
first stripped the soil and redistributed it. Then the winds blew them around. The
loess is a finely ground silt with some clay and some sand. Loess is a very
good agricultural soil and lucky for us it covers about 20% of the land surface
of the Earth, mostly in temperate regions. Loess is highly erodible by wind and
rain. In the U.S. the buffalo grazed the loess for two hundred thousand years,
manuring it as grasses grew and protected it from erosion. In 1838 John Deere
and a partner invented a plow capable of tearing up the rough and tick prairie
turf with deep rooted grasses. Cyrus McCormick’s mechanized harvester was another
innovation. These inventions allowed farmers to farm more land and more tough-to-farm
land. They also exposed more soil that was eroded quickly. The Great Plains
were heavily plowed between 1870 and 1900. In 1902 the U.S. Geological Survey
warned that these soils were very vulnerable to erosion.
Soil erosion caused
economic harm when farms had to be abandoned. Mechanization made it even easier
to simply plow new land when old land degraded. New equipment increased yields
and profit but was also costly in bad years as farmers added debt and made farming
more capital-intensive and crowded smaller operations out. By the 1930s tractor
use increased in the U.S.
“New disk plows, with rows of concave plates, set out
along a beam, thoroughly diced the upper layers of soil, leaving a pulverized
layer that could easily blow away in dry conditions.”
The first windstorm of the Dust Bowl years occurred in 1933
in North Dakota. Some farms lost their topsoil in a single day. The sky became
dark with soil on the wind. A storm occurred in May 1934 the brought dark
clouds of dust moving across the country and out into the Atlantic Ocean.
Another spring windstorm in 1935 brought soil from Kansas, Texas, Nebraska, Oklahoma,
and Colorado. Loess blew on the wind darkening the sky and the heavier sand moved
closer to the ground piling up in dunes. In 1935 the U.S. Senate initiated the founding
of the Soil Conservation Service (SCS). The Dust Bowl was so bad that about three-quarters of a million farmers were left without a livelihood and headed west. Poor
farming practices were implicated in the Dust Bowl. Walter Lowdermilk became Associate
Chief of the SCS. He implemented a program to compare soil erosion rates in
undisturbed areas and compare them to farmed areas by county. This assessment
revealed the scope of the problem.
“From one- to three-fourths of the topsoil was gone from
two-thirds of a billion acres, more than a third of the area surveyed.”
In the 1950s Lowdermilk argued that the history of farming
showed conclusively that farming slopes was dangerous. Droughts occurred in the
1950s and the SCS was credited with preventing another Dust Bowl. Soil
conservation programs became a part of farm subsidies begun in the 1930s. Soil
loss increased as an issue after the advent of synthetic fertilizer and increased
mechanization, which accelerated erosion. Mechanization also decreased some positive
practices such as terracing, hedgerows, and windbreaks.
In 1979 the SCS
reported that just three decades of plowing in the Palouse region of Eastern Washington
state had lowered fields by as much as three feet below unplowed grassland. Even
this big of a change is hard to notice year by year in some places. It’s the same
story of plowing, exposure to storms, and massive erosion. Erosion typically
occurs in spring but can occur anytime fields are plowed.
The Soviets had
their dust bowl years in the 1950s and 60s as more marginal land was ordered to
be plowed, even after they knew the risks from the American example. The Soviet Dust Bowl helped drive Krushchev from office. The building of canals and diversion
dams led to much of the Aral Sea drying up which then resulted in wind carrying
silt and salt to Russian farms up to a thousand miles away in the 1990s. Extensive
plowing caused catastrophic soil erosion all over the world. He goes through
many examples. In some places like Africa’s Sahel region droughts and
overgrazing were also implicated in the devastating desertification.
He also addresses
urbanization and paving over land as a means to increase erosion rates and lose
otherwise productive land. He notes that keeping erosion rates under 1 ton per
hectare per year, about 1 inch of erosion in 250 years is required to balance
it with the rate of soil formation on average. He notes that the time it takes
nature to produce an inch of soil varies from about 160 years in
heather-covered Scotland to more than 4000 years under deciduous forest in Maryland.
The average is between 240 years and 820 years, or 0.37 to 1.29 tons per
hectare per year.
“The 1977 Soil and Water Resources Conservation Act
required the USDA to conduct an intensive appraisal of the nation’s soil. Four years
in the making, the 1981 report concluded that American soil still eroded at an
alarming rate more than four decades after the Dust Bowl.”
Soil conservation
works, according to USDA estimates:
“Recent USDA estimates show soil erosion from U.S.
cropland as dropping from about three billion tons in 1982 to just under two
billion tons in 2001, substantial progress to be sure – but still far ahead of
soil production.”
An economic analysis
by Cornell University’s David Pimentel in the 1990s showed that money invested
in soil conservation would result in saving five dollars for every dollar
invested. Of course, farmers are often not able to make those investments and
need help from the government.
Montgomery does
call out overblown alarmist predictions of loss of agricultural land like those
of Lester Brown. He also argues that smaller farms can have higher yields and
better conservation practices than larger ones, especially monoculture ones. However,
I think the larger farms are now better addressing soil erosion so that may not
be true these days.
Next, he goes
through rice paddy agriculture in China and how the use of human waste in the
fields helped to make them more fertile.
In the 1800s
scientists discovered the importance of nutrients, nitrogen, phosphorus, and
potassium (N, P., and K) and agrochemistry was born. Later that century and well
into the next phosphorus was obtained from bird guano deposited on islands off
of Peru. These supplies were eventually exhausted. The discovery of calcium phosphate
rock deposits in South Carolina, Tennessee, and Florida, less potent than guano
but more abundant, led the U.S. to be the main producer and exporter of
phosphates to Europe in the early decades of the 1900s. Phosphorous depletion
in American soils was already becoming apparent.
California has
alkali soils. These were extensively irrigated which raised local water tables.
When the water evaporated it would bring more salt up into the soil from below
through capillary action.
Nutrients alone could
not improve yields if they were not available to the plants. In the early 1900s, some soil scientists thought that all soils were as fertile as chemical analysis
would show. However, this was proved incorrect.
“… the amount of nutrients in soil solutions differed from
amounts suggested by total chemical analysis of soil samples but correlated
with crop yields.”
Loss of nitrogen in
soil was another big problem. It could be added by applying manure, but the
supply of manure was not enough. After Carl Bosch and Fritz Haber perfected the
Haber-Bosch process of capturing nitrogen from the air in the 1910s. In the
1920s the process was modified to use methane as the feedstock for producing
ammonia. The process was finally commercialized in California in 1929. Production
exploded in the U.S. in the 1950s as more fertilizer plants were built in
natural gas-producing regions and ammonia was pipelined to where it was needed
in the corn belt. The Soviets had similar success. Nitrogen became readily available
and cheap.
New forms of
wheat developed by Norman Borlaug in the 1960s and 70s were heavy feeders that
required lots of nitrogen and thus it was synthetic nitrogen that fueled the
Green Revolution. This combo of new crops and heavy fertilization helped to stave
off hunger and feed the world and it still does.
“The USDA estimates that about half of the fertilizer
used each year in the United States simply replaces soil nutrients lost by
topsoil erosion.”
While synthetic
fertilizer is a huge boon to yields it cannot replace the traditional and
modern practices of soil conservation if we are to stave off soil loss. Montgomery
details some of the benefits of organic farming such as composting. Composting and
soil conservation can be added to modern mechanized agriculture. Leaving and
turning under crop residues was one way of composting.
With plowing
arguably causing more harm than good, Edward Faulkner, author of Plowman’s
Folly in the 1940s noted:
“The net effect of fertilizing the land, then, is not to
increase the possible crop yield, but to decrease the devastating effects of
plowing.”
Les Jackson at
the Land Institute in Salina Kansas also noted the negative effects of plowing.
Jackson incorporated the deep-rooted perennial prairie grasses into his
agricultural trials, noting that they hold the soil together, preventing
erosion. He practiced perennial polyculture by growing multiple yearly crops,
noting that monoculture was responsible for much of the soil erosion. Montgomery
notes and I agree:
“We can greatly improve conventional farming practices
from both environmental and economic perspectives by adopting elements of
organic {farming} technologies.”
Organic farming does have lower yields, although not that much
lower, but it conserves soil much better.
“Today, a middle ground is evolving in which nitrogen-fixing
crops grow between row crops and as cover in the off-season, and nitrate
fertilizer and pesticide are use”d at lower levels than on conventional farms.”
There is now less plowing as no-till methods are adopted. Simply
discing crop residue into the soil without any deep plowing has proven
effective. Montgomery notes:
“Changes in farming practices over the past several
decades are revolutionizing modern agriculture, much as mechanization did a
century ago – only this time, the new way of doing things conserves soil.”
He notes that conservation tillage and no-till methods were
used on 60% of Canadian farms by 2001. They are now standard. By 2004
conservation tillage was used on 41% of U.S. cropland and no-till methods on 23%.
This has increased since then.
“No-till farming is very effective at reducing soil erosion;
leaving the ground covered with organic debris can bring soil erosion rates
down close to soil production rates – with little to no loss in crop yields. In
the late 1970s, one of the first tests of the effect of no-till methods in
Indiana reported a 75 percent reduction in soil erosion from cornfields.”
“The Food Security Acts of 1985 and 1990 required farmers
to adopt soil conservation plans based on conservation tillage for highly erodible
land as a condition for participating in popular USDA programs (like farm subsidies).
But conservation tillage has proven to be so cost-effective that it also is
being widely adopted on less erodible fields.”
It can reduce fuel use so much that slightly lower yields is
more than compensated and profits increase. He notes that no-till agriculture
can also help reduce climate change.
“A third of the total carbon dioxide buildup in the
atmosphere since the industrial revolution has come not from fossil fuels but
from degradation of soil organic matter.”
No-till methods work better in sandy and silty soils and do
not work well in heavy clay soils which tend to become compacted. No-till
methods also require more pesticides at the beginning, before soil biota is
built up. Farmers in developing countries have yet to adopt it enough.
He has a chapter
about soil erosion and degradation on island nations such as Easter Island,
other Polynesian Islands, and Iceland. The particulars are different, but the
basic story is the same. In Iceland, layers of volcanic ash were easily blown
away when exposed due to agriculture and overgrazing. Iceland lost 60% of its
vegetative cover and 96% of its tree cover after 1100 years of habitation. Haiti
and Cuba offer similar stories of severe soil loss, in those cases due to
farming monocultures like sugar cane for export. I read recently that Cuba now
imports sugar cane. The U.S. embargo against Cuba forced it to adopt soil
conservation methods in order to have enough food. Their methods, however, are
very labor-intensive, and not viable for much of the world. They did, however,
help prove the validity of soil conservation in preserving soil and yields.
“Whether, and the degree to which, soil erosion exceeds
soil production depends on technology, farming methods, climate, and population
density.”
He notes that on average people have increased soil erosion
around the world by about ten times.
The future of
farming seems to be one where soil conservation, no-till methods, traditional
methods, organic farming, mechanization, and synthetic fertilization are
combined. He mentions new methods of precision application of nitrogen and phosphorus
and methods for retaining soil organic matter and fertility.
“In general, species-rich tropical latitudes tend to have
nutrient-poor soils, and the world’s most fertile soils are found in the
species-poor loess belts of the temperate latitudes.”
The loess belts are the only regions that can sustain
intensive mechanized agriculture over time.
Well, that’s
about it for this summary and review. It’s a fascinating book that tells histories
and stories many do not know about our soils and the importance of conserving
them.
