ÐÓ°ÉÔ­´´

Land farmed without fertilisers or pesticides can be just as productive
as land pumped full of chemicals. More important still, organic farming
preserves the land’s most precious commodity, the soil

AMONG the rolling hills of the Palouse region of eastern Washington
State lie two neighbouring farms. The two have much in common: they lie
on the same type of land and share the same soil; both have been worked
since the early years of the century. But there is a crucial difference.
One is an organic farm; it has relied on green manure crops, crop rotation
and the natural fertility of the soil since first ploughed in 1909. The
adjoining farm, slightly larger and cultivated a year earlier, became a
‘conventional farm’, nourished by fertilisers from 1948 and protected by
pesticides since the early 1950s. Together, these two farms offer the opportunity
to settle some of the many arguments about the pros and cons of each system
of farming.

Until recently, the agricultural establishment viewed organic farming
as unproductive and inefficient. In spite of this, interest has grown because
many farmers are looking for ways to reduce the amount of expensive fertilisers
and pesticides they use. Organic agriculture is gaining other adherents
who regard it as a way to remedy, or at least to lessen, the damage that
modern agriculture does to the soil, the environment and the health of both
humans and animals.

What we describe as conventional agriculture is of recent origin. With
the appearance of cheap fertilisers at the end of the Second World War and
pesticides in the early 1950s, advanced countries quickly abandoned traditional
or organic methods of farming and became heavily dependent on both agrochemicals
and labour-saving machinery. Farmers relinquished organic methods not because
they did not work but because they could not compete with the new type of
agriculture. But the modern concept of organic farming is not a return to
the past, rather a marriage of scientific advances with many traditional
practices.

The US Department of Agriculture considers organic farming to be a system
that avoids or excludes the use of synthetic fertilisers and pesticides
and relies upon practices such as crop rotation, the use of animal and green
manures, and some forms of biological pest control. Most organic farmers
use modern machinery, recommended varieties of crops, certified seed, sound
methods of livestock management, prescribed practices for conserving soil
and water, and innovative methods of managing crop residues.

In 1985, Lloyd Elliott, a colleague at Washington State University,
told me of two old farms, one organic and the other conventional, where
the history was known and we could compare the soils in detail. Elliott
had worked previously with two graduate students, Harvey Bolton and Andrea
Weilgart Patten, on a study of some of the biological and chemical aspects
of the soil on the two farms. Elliott and I decided, with the help of a
student, Yvonne Unger, to look at the physical properties of the soils and
the rates of erosion. Our study is one of the few systematic comparisons
that gives a detailed picture of the effects organic and conventional agriculture
have on the quality of soil and on erosion on working, commercial farms.

The 80-year-old organic farm has been managed without inorganic fertilisers
and only limited use of pesticides (first applied in the mid-1960s and only
to spring peas). The farm grew winter wheat, spring pea and a green manure
crop (for one to two years) in a three to four-year rotation. The conventional
farm had a two-year crop rotation of winter wheat and spring pea, with pesticides
applied to both. The organic farmer grew a green manure of either Austrian
winter pea for one year (in a three-year cycle) or a mixture of alfalfa
and grass for two years (in a four-year cycle). The green manure was always
completely turned under in the soil. A green manure crop is usually a legume,
such as alfalfa, sweet clover or Austrian winter pea; legumes enrich the
soil with nitrogen compounds and with organic matter.

The study area (roughly 100 metres by 50 metres) lies on a 4-degree
slope at the juncture of the two farms. The validity of this research is
based on the assumption that all environmental conditions and soil properties
at the site were similar until 1948. Any differences today can be attributed
to the fact that after 1948 one farm was managed organically and the other
conventionally.

Soil microorganisms enrich the soil as they live and die and are indispensable
in their influence on crop production. They are a kind of hidden workforce
that provides many key benefits. The most important of these are the breakdown
of organic matter in the soil to humus and the release of nutrients held
in organic combinations, which plants can then use. Microbes also help to
stabilise soil aggregates, fix nitrogen and break down some pesticides.
In 1983, Bolton found that the soil on the organic farm contained a much
higher mass of microbes and showed much more enzyme activity than the soil
on the conventional farm. Soil enzymes are derived primarily from microorganisms
in the soil. These results indicated that the organic farm had larger and
much more active populations of microbes in its soil.

Elliott and I later found almost 60 per cent more organic matter on
the surface of the soil on the organic farm. These results support the findings
of other researchers that organic farmers can, and generally do, achieve
higher concentrations of organic matter in their soils than conventional
farmers. They also help to explain the greater microbial activity in the
organically farmed soil: the more decayed organic matter there is, the more
microbes it will feed.

Organic matter has a profound impact on the quality of the soil; it
encourages mineral particles to clump together to form granules, improving
the structure of the soil; it increases the amount of water the soil will
hold and the supply of nutrients; and the organisms in the soil are more
active. All in all, organic material makes the soil more fertile and productive.
In our experimental plots, we found that the soil on the organic farm was
well-granulated, the best structure for most ordinary crop plants; the other
soil was not. The organically farmed soil also contained much more moisture;
its cation exchange capacity (a measure of the soil’s capacity to store
nutrients) was greater; the total amount of nitrogen and available potassium
were also much larger. Most of the extra organic matter came from green
manure.

The presence of microbes brings other benefits. As the microbes break
down organic material they produce polysaccharides, gummy substances that
can stabilise the soil by binding particles into aggregates. Aggregates
are less vulnerable to breakdown and erosion. Soil organisms also break
down polysaccharides, however. So farmers must continue to add organic matter
to the soil to maintain a supply of these stabilising substances.

The organic soil had a significantly lower ‘modulus of rupture’, an
index related to the hardness of the crust that forms on the surface of
the soil. In general, the lower the modulus of rupture, the easier it is
for seedlings to emerge. The combination of all these factors gives the
organically farmed soil better tilth than the soil on the conventional farm.
The better the tilth, or physical condition of the soil, the easier it is
to till and the easier it is for plants to germinate and push out shoots
and roots.

The study area where we sampled the soil was made up of one type of
soil called Naff silt loam. A typical Naff soil has two distinct layers:
the dark-coloured surface layer, called an ‘A’ horizon, has a texture of
silt loam and is between 20 and 70 centimetres thick. The ‘A’ horizon makes
up the topsoil, the richest and most easily tilled layer of the soil. The
subsoil is a strong, silty clay loam ‘Bt horizon’ extending to a depth of
up to 150 centimetres. Clay accumulates in the Bt horizon making it dense,
sometimes to the extent that it cramps roots. The subsoil is less fertile
than the topsoil.

The layer of crop-nourishing topsoil on the organic farm was about 16
centimetres thicker than on the conventional farm. This difference was not
because of a build-up of topsoil but because the soil on the conventional
farm was eroding much more quickly. Erosion not only continuously thins
the topsoil, it also brings the subsoil nearer to the surface. When Bt layers
reach the surface, they show as lighter-coloured ‘clay knobs’ on the landscape.

Andrea Weilgart Patten studied water erosion in our test area. She measured
rill erosion (a type of water erosion in which many small channels form)
on the two fields when both farms were growing winter wheat. The results
were impressive: water erosion removed 32.4 tonnes per hectare on the conventional
field, but only 8.3 tonnes per hectare on the organic field. Interestingly,
the rate of erosion on the conventional farm is close to the average annual
rate for the area, which is farmed almost entirely by conventional methods.
I also estimated rates of water erosion based on the Universal Soil Loss
Equation developed by Walter Wischmeier in the US. The theoretical losses
were 20.4 tonnes per hectare on the conventional farm and 7.8 tonnes per
hectare on the organic farm.

The scale of soil erosion is hard to grasp when described in terms of
tonnes per hectare. But a little over 1 tonne of soil distributed over a
hectare of land would form a layer of soil the thickness of a sheet of paper.
The loss of a few tonnes of soil is the equivalent of peeling off a few
pieces of paper. Erosion is an insidious problem because in many cases it
is almost unnoticeable. Loss of 20 tonnes per hectare is almost invisible,
but over the years the cumulative effect can be dramatic. Soil takes so
long to form, yet it can be destroyed so quickly.

What do all these estimates mean? What should we regard as excessive
erosion when considering the quality of the soil in the long term? The US
Department of Agriculture’s Soil Conservation Service has developed a concept
of ‘soil loss tolerance’. The so-called ‘T’ value is the maximum rate of
erosion that can occur without reducing the productivity of crops in the
long term or the environmental quality of a specific soil. T values commonly
range between 4.5 and 11.2 tonnes per hectare. According to the Soil Conservation
Service, as long as farmers keep the rate of erosion below the T value,
their fields should produce high yields indefinitely. However, the scientific
basis for T values is controversial because researchers disagree about how
long it takes both topsoils and complete soils to thicken or form. The two
estimates of erosion made for the conventional farm are either two or three
times the maximum T value of 11.2 tonnes per hectare for Naff soils. The
two measurements of water erosion on the organic farm are less than three-quarters
of the maximum T value. Our findings suggest that Naff soil on the organic
farm will maintain its productivity in the long term, whereas the soil on
the conventional farm is becoming less productive as a result of erosion.

The Palouse region, covering an area of 0.7 million hectares, is a distinctive
geological terrain of rolling hills and deep loess (formed from materials
blown in by the winds over the past million years). It is one of the world’s
most productive regions for growing wheat and peas without irrigation. It
is also one of the most rapidly eroding landscapes in the US because of
the combination of farming practices and steeply rolling hills. Since the
land was first cultivated more than a century ago, 10 per cent of the cropland
has lost all of its original topsoil. Between a quarter and three-quarters
of the original topsoil has disappeared from a further 60 per cent of the
region’s arable land. The loss of the topsoil has presented the farmers
of the Palouse with problems in their tillage operations, preparation of
seedbeds, emergence of seedlings and soil fertility.

Erosion is one of the greatest threats facing American farmers in many
regions of the country. The US Department of Agriculture’s National Resources
Inventory for 1982 showed that about 44 per cent of arable land is eroding
faster than the soil conservation service considers tolerable. Inter-estingly,
the National Soil Map, published by the Soil Survey of England and Wales
in 1986, also indicated that 44 per cent of the arable soils in England
and Wales are at risk from erosion by water and wind.

Alternative futures

Though the two fields in this study have the same type of soil and were
probably virtually identical 40 years ago, the topsoil is now eroding more
rapidly on the conventional field. At this rate, all the topsoil on typical
Naff and similar soils under conventional farming systems will be lost in
another 50 to 100 years. When this happens, wheat yields from these soils
could fall by one-third or more. The organic farmer should be able to maintain
the topsoil for generations to come, although he could slow the rate of
erosion still further by adopting other practices to conserve soil.

Technological advances in the form of new fertilisers, pesticides, and
plant varieties mask the decline in productivity as a result of erosion.
Intensive farming has produced record-breaking yields year after year, but
production could fall substantially in the coming decades. Research has
shown that technological advances have the greatest potential for increasing
yields on deep, relatively uneroded topsoils. If erosion continues at its
present rate, the topsoil will finally become so thin that fertilisers will
fail to increase yields, and then they will begin to decline.

The average yields of winter wheat between 1982 and 1986 were 8 per
cent lower on the organic farm than on the conventional farm, but almost
13 per cent higher than on a second conventional farm (with similar soils)
nearby. Wheat production on the organic farm matches the average for the
Spangle area, the portion of the Palouse where the farms are. The ability
of the organic farmer to produce yields similar to neighbouring conventional
farmers, even after almost 80 years of farming without fertiliser, may be
attributed in part to a reduction in soil erosion through effective management
of the soil.

The difference in the rate of erosion between the two farms can be credited
mostly to different systems of crop rotation. The organic farmer uses a
legume as a green manure, whereas the conventional farmer does not. By ploughing
in a green manure, the farmer increases the amount of organic matter in
the soil, which improves infiltration of the soil water and reduces runoff
that washes away soil. While the green manure crop is growing, it also protects
the soil from being broken up by rain, dissipating the force of falling
raindrops (see ‘Solutions to soil erosion’, New ÐÓ°ÉÔ­´´, 3 June 1989).
Rotation systems that include a legume can also help to control weeds and
insects as well as provide forage for livestock and shelter for wildlife.

As the organic farmer removes his land from production of either wheat
or peas every third year, his overall output is smaller than the conventional
farmer’s by another one-third for the same amount of land. But, in the long
run, it is the conventional farmer who loses – both his soil and his productivity.
Although most farmers abandoned the practice of green-manuring with legumes
in the late 1940s and early 1950s, there is no reason why they could not
revive the custom.

Another practice that plays a part is tillage. The organic farmer regularly
used both chisel and mouldboard ploughs, whereas the conventional farmer
used the mouldboard plough and disc in his tillage operations. Studies have
shown that chisel ploughing causes less erosion than the mouldboard plough
and disc because it leaves the surface soil rough and covered with crop
residues. A chisel plough also penetrates the dense layers of soil compacted
by tillage operations, allowing water to drain through rather than washing
over the soil. The mouldboard leaves the soil more vulnerable to erosion
because it turns over the soil and buries the crop residues that offer the
soil some protection. A disc helps to bury the residues and pulverises and
smooths the soil, leaving it still more susceptible to erosion. These differences
in tillage practices may have contributed to the difference in the rate
of water erosion on the two farms.

Since my colleagues and I conducted these studies, I have been asked
why we did not compare the production costs of the two systems and correlate
them with yields. First, we did not have the economic data; but I feel safe
in saying that the organic farm is cheaper to run because the farmer does
not have to buy fertiliser and needs smaller amounts of pesticide. Secondly,
our aim was simply to examine the soil. In a landmark study, William Lockeretz
and his colleagues at Washington University in St Louis, Missouri, had already
made economic comparisons of numerous matched pairs of organic and conventional
farms in the American Midwest.

Between 1974 and 1978, the organic farms in the Lockeretz study produced
lower yields than the conventional. But operating costs on the organic farms
were also lower by about the same amount. As such, the income from each
hectare of cropland was about equal for the two types of farm. In addition,
the amount of energy spent to produce the crop was dramatically different
on the two types of farm: the organic farms required about 40 per cent of
the fossil fuel the conventional farm used to produce crops of the same
value.

Because of decisions two farmers made four decades ago, the two farms
in Palouse today illustrate how different methods of farming affect one
of the country’s most precious, though often overlooked, natural resources
– its topsoil. In the late 1940s and 1950s, the conventional farmer, like
almost all farmers in the US, abandoned traditional farming methods in favour
of intensive, high-technology agriculture. The organic farmer stuck to tradition.
And from the measure of topsoil and other soil characteristics, he appears
to have made the right decision. We worry about whales and sea otters, and
rightly so. But, in general, we do not concern ourselves with soil, because
most of us live in cities, unaware of the inherent value of soil. We rearrange
and restructure it, pump it full of chemicals, and otherwise abuse it. Our
obligation as farmers and as society is to put soil before profits. But
we do just the opposite. Many farmers know how to control erosion, but soil
conservation is driven by economics. Unfortunately, the benefits of conservation
rarely show immediately, perhaps not for 5, 10 or 20 years. In the short
term, soil conservation may not repay a farmer in profits what he had to
spend to save the soil. But unless many farmers alter their techniques and,
where necessary, are supported by government farm programmes, they may be
sacrificing our future food supply.

John Reganold is an associate professor in the department of agronomy
and soils at Washington State University, Pullman, Washington.