United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA-600/S3-82-027 Sept. 1982
Project Summary
Conservation Tillage and
Conventional Tillage:
A Comparative Assessment
Pierre Crosson
The objective of this study was to
reach a judgment of the amount of
U.S. cropland likelyto be insome form
of conservation tillage in 2010. The
future spread of conservation tillage
will be conditioned primarily by
farmers' perceptions of its economic
advantages relative to conventional
tillage and by society's perceptions of
its advantages and disadvantages
with respect to the environment.
Accordingly, the study first considers
the economics of conservation tillage
relative to conventional tillage, exam-
ining differences between the two
technologies in the quantities of
resources used and in yields. The
conclusion is that conservation tillage
typically uses less of certain resources
and more of others, but that on
balance it requires 5 to 10 percent less
expenditure per acre than conven-
tional tillage. Yield differences vary
widely, depending fundamentally on
soil characteristics and climate, but on
well-drained soils in the Corn Belt,
Southeast, and much of the Northern
and Southern Plains where weeds can
be controlled by herbicides, yields
with conservation tillage are fully
competitive with yields of conven-
tional tillage. The conclusion is that
the economic advantages of conser-
vation tillage could induce farmers to
adopt it on 50 to 60 percent of the
Nation's cropland by 2010. A little
less than 25 percent of cropland was
in conservation tillage in 1979.
This Project Summary was devel-
oped by EPA's Environmental Re-
search Laboratory, Athens. GA, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Prospective growth m agricultural
production and crop yields indicates
that over the next three decades the
demand for cropland in the United
States could increase by 60 to 70 mill ion
acres. The present supply of cropland is
fully used so the additional acres would
have to come from land now in pasture,
forest and range. Much of this land is
subject to high erosion hazard. Convert-
ing it to crops will greatly increase
erosion and consequent damages to
water quality and to the productivity of
the land unless protective measures are
taken.
Except on level land, the amount of
erosion from an acre of cropland is
greatly influenced by the kind of tillage
technologies farmers employ. Tillage
that completely inverts the soil and
buries all crop residue generally will
leave the land much more exposed to
the erosive forces of wind and water
than tillage that turns the soil less and
leaves much crop residue on the
surface. The latter kind of technology is
called conservation tillage to distinguish
it from conventional tillage. Conserve-
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tion tillage covers a variety of tillage
practices, but they all have three
features in common: (1) they use some
instrument other than the moldboard
plow to prepare the seed bed; (2) they
leave enough crop residue on the soil
surface to significantly reduce erosion;
and (3) they rely less on cultivation and
more on herbicides to control weeds
than conventional tillage. The distin-
guishing characteristics of conservation
tillage and conventional tillage are
shown in Table 1.
The magnitude of the erosion hazard
the nation will face overthe next several
decades will be much influenced by the
extent to which farmers adopt conser-
vation tillage. The rate of adoption will
be determined fundamentally by the
economic advantages of conservation
tillage relative to conventional tillage
and by public policies, which may favor
or impede adoption. Policies favoring
adoption may be developed because of
the advantages of conservation tillage
in reducing erosion. Policies impeding
adoption may come into play if it
appears that the greater reliance of
conservation tillage on herbicides
threatens unacceptable environmental
damage.
This study investigates the compara-
tive economics and environmental
impacts of conservation tillage and
conventional tillage to reach a judgment
about the spread of conservation tillage
over the next three decades.
Economics of Conservation
Tillage and Conventional
Tillage
Quantities of Resources
Conservation tillage evidently has
some economic advantages over con-
ventional tillage. This is indicated by its
spread since the mid-1960s (Table 2), a
period in which policies to encourage
conservation tillage went little if any
beyond exhortation by the Soil Conser-
vation Service (SCS) and various state
conservation agencies.
On a per acre basis conservation tillage
requires less pre-harvest labor and less
fuel than conventional tillage. A farmer
who opts 100 percent for conservation
tillage also will have lower machinery
investment costs, but the extent of this
advantage is obscure because many
farmers will want to retain the capacity
for conventional tillage also.
The savings in labor and fuel occur
because the farmer makes fewer passes
over the field with his tractor for land
Table 1. Distinguishing Characteristics of Conservation Til/age and Conventional
Til/age
Tillage System
Characteristic
Tillage instrument
Crop residue on soil
surface
Weed control
Conservation
Not the moldboard plow
Enough to significantly
reduce erosion
Primarily herbicides,
but may a/so cultivate
Conventional
Moldboard plow
Little or none
Mechanical cultivation
more important than with
conservation til/age, but
herbicides typically
used also
Table2. Land in Conservation Tillage in the U.S.
(millions acres)
1965
1973
1975
1976
1977
1978
1979*
USDA
6.6
29.5
35.8
39.2
47.5
51.7
55.0
%of
Harvested
Cropland
23
9.3
10.8
11.8
14.1
15.6
16.1
/v
No-Till]
NA
4.9
6.5
7.5
7.3
7.1
7.6
:o-i in i-armer
Minimum
Till\
NA
39.1
49.7
52.1
62.7
67.7
71.6
Total
NA
44.0
56.2
59.6
70.0
74.8
79.2
%of
Harvested
Cropland
NA
13.9
17.0
18.0
20.7
22.6
23.2
*Preliminary.
tDefined as "where only the intermediate seed zone is prepared. Up to 25 percent of
surface area could be worked. Could be no-till, till-plant, chisel plant rotary strip
tillage, etc. Includes many forms of conservation tillage and mulch tillage." Obviously
the numbers in this column reflect tillage practices other than no-till.
^.Definedas "limited tillage," but where the total field surface is still worked by tillage
equipment.
preparation and cultivation to control
weeds. The saving in machinery is
because a less powerful, therefore less
expensive, tractor can handle the more
shallow tillage characteristic of conser-
vation tillage.
The savings in labor, fuel and machin-
ery (if any) vary widely among farmers
depending upon local circumstances.
Roughly, however, the saving in pre-
harvest labor is on the order of 50
percent. No-till, an extreme form of
conservation tillage, saves 3to4gallons
of diesel fuel per acre and other forms of
conservation tillage save 1 to 3 gallons.
The machinery investment saving,
assuming 100 percent adoption of
conservation tillage, is about $5 per
acre.
Some of the literature on tillage
technologies suggests that losses of
nitrogen fertilizer are higher with
conservation tillage than with conven-
tional tillage so that more is required to
achieve a given yield. Other parts of
the literature dispute this, however. In
this study it is assumed that per acre
amounts of fertilizer used with the two
•technologies are the same.
The literature suggests that conser-
vation tillage requires more skilled
management than conventional tillage.
A number of reasons typically are given:
fewer passes over the field mean fewer
opportunities to correct previous mis-
takes in plowing and planting; the
surface residue makes it more difficult
to get good seed placement, requiring
extra care in this crucial operation;
weed, insect and disease problems
likely will be more complex, requiring
more knowledge of the properties of a
wider variety of pesticides and of howto
apply them, or of crop rotations and
disease and insect resistant varieties as
substitutes for pesticides; more know-
ledge of machinery characteristics and
more care in machinery operation and
maintenance.
The requirement for more skilled
management with conservation tillage
is real enough, but it is doubtful that this
adds significantly to the costs of the
technology. The history of American
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agriculture since the end of World War II
indicates that American farmers can
quickly learn to manage new technolo-
gies when it is in their economic interest
to do so. Acquiring the management
skills needed for successful conservation
tillage would require some investment by
farmers of time and perhaps financial
resources, but amortized over time the
skills would be employed, their cost
almost surely would be small.
Conservation tillage typically requires
more pesticides per acre than conven-
tional tillage. The crop residue left on
the soil surface provides an environment
favorable to insects and diseases, and
herbicides to a large extent substitute
for cultivation to control weeds. The
requirement for more herbicides is
more clearly demonstrated than that for
more insecticides and fungicides. Most
of the insecticides applied to conservation
tilled land is land corn. The quantity of
insecticides used on corn increased 50
percent from 1 971 to 1976, a period in
which conservation tillage in corn was
spreading rapidly. However, the amount
of insecticide applied per acre of corn
land receiving treatment declined.
Although conservation tillage does
increase the threat of disease, the
favored treatment is use of disease-
resistant varieties rather than more
fungicides.
There are three reasons why conser-
vation tillage typically requires more
herbicides than conventional tillage.
One is the substitution effect. If control
of weeds by tillage is reduced then a
compensatory increase in herbicides is
necessary to maintain the same level of
control. There also is an efficiency
effect. Some of the herbicide gets tied
up by the crop residue so more is
required to do the job. Finally, there is an
environmental effect. The surface
residue typically reduces evaporation of
water, resulting in more moist soil. This
favors germination and growth of
weeds.
On balance, the lower requirements
of conservation tillage for labor, fuel and
machinery more than offset the greater
requirement for pesticides. The effect
on costs is not clear, but by a rough
estimate, per acre costs of conservation
tillage, exclusive of land, are 5 to 10
percent less than costs of conventional
tillage.
If there were no differences in yields
between the two tillage systems then
these cost differences would imply rapid
substitution of conservation tillage for
conventional tillage. Indeed substitution
is implied even with lower yields for
conservation tillage so long as the
difference is not more than 5 to 10
percent. Obviously the yield performance
of the two technologies must be
considered.
Yields
It is important to distinguish between
the short-term (one or two years) and
long-term (decades) yield effects of
tillage technologies. Over the long term
the lower rates of erosion associated
with conservation tillage can give it a
decisive yield advantage relative to
conventional tillage. Whether this
occurs depends upon (1) the differential
advantage of conservation tillage in
reducing erosion; (2) the amount of
topsoil and the nature of the underlying
parent material; and (3) the relation of
changes in the amount of topsoil to
changes in yield over time.
Depending upon these three condi-
tions, the effect of the erosion factor in
the choice of tillage technologies is
either neutral or it favors conservation
tillage It can never favor conventional
tillage. Consequently, where conserva-
tion tillage confers a short-term yield
advantage farmers will always choose
that technology (given its cost advantage
depicted in the previous section). Even
where short-term yields of conservation
tillage are less, however, farmers may
yet choose that technology over conven-
tional tillage if the erosion advantage of
conservation tillage is sufficiently
strong.
The advantage of conservation tillage
will be (1) the greater annual yield
difference between conservation and
conventional tillage as determined by
the three factors listed above; (2) the
higher cost to the farmer of substituting
fertilizer or other inputs for the lost soil;
(3) the longer length of time over which
the yield differences matter to the
farmer; (4) the higher the farmer
expects future crop prices to be relative
to current prices; and (5) the lower rate
of discount the farmer applies to future
earnings.
It is likely that real fertilizer prices will
rise over the next several decades
(factor (2) above). Other things the same,
this would strengthen the long-term
yield advantage of conservation tillage
over conventional tillage. Little is known
however, about the effect of erosion on
yields, about the length of the farmer's
time horizon, his expectations about
future crop prices or his rate of discount.
Consequently, the only confident state-
ment we can make is one already made
above: since conservation tillage never
produces more erosion than conventional
tillage and typically produces much less,
the erosion effect on yields can never be
to the disadvantage of conservation
tillage. At worst it will be neutral, and it
must often be positive, although without
much additional research we cannot
identify the specific situations in which
this would be true or estimate the
strength of the advantage.
The question of the long-term yield
effects of erosion would be moot if
conservation tillage had a clear short-
term yield advantage over conventional
tillage. In fact, short-term yield differ-
ences vary widely from place to place
and time to time, with conservation
tillage yields sometimes higher and
sometimes lower. Some generalizations
are warranted, however. Conservation
tillage generally conserves soil moisture.
This conveys a yield advantage in semi-
arid areas and wherever soils are
droughty. It is a disadvantage, however,
on poorly drained soils, primarily
because excessive moisture m these
soils fosters plant diseases.
Because of the surface residue soil
temperature in the spring generally is
lower with conservation tillage, and this
may delay seed germination and seedling
emergence, a disadvantage where
growing seasons are short, as in the
northern tier of states.
Finally, conservation tillage is at a
distinct disadvantage wherever weeds
cannot be adequately controlled with
herbicides. Perennial weeds in particular
may become troublesome because
cultivation generally gives better control
of these weeds than herbicides. Indeed,
a theme running through the literature
is that conservation tillage should not be
tried wherever perennial weeds flourish.
Summary on Economics
Resource costs with conservation
tillage are 5 to 10 percent less than
costs of conventional tillage. On well
drained soils in regions where the
growing season is not too short and
weeds can be adequately controlled
with herbicides, yields with conservation
tillage are comparable to yields with
conventional tillage. These conditions
are widely enough met that, with
present technologies and practices,
conservation tillage should prove eco-
nomical on 50 to 60 percent of the
Nation's cropland.
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Environmental Impacts of
Conservation Tillage and
Conventional Tillage
The objective of the discussion is to
reach judgments about differences
between the two technologies with
respect to environmental damages from
erosion and from pollution by pesticides
and fertilizers.
Erosion
By weight, eroded soil is by far the
biggest polluter of surface water in the
United States. It may impair recreational
values, harm fish, and when it settles
shorten the useful life of reservoirs and
clog harbors, requiring expensive
dredging operations to clear it away.
Erosion also will eventually reduce
the productivity of the land, the amount
of the reduction depending upon the
depth of topsoil, the rate of erosion,
nature of the underlying material,
climate, and other factors. The produc-
tivity effects of erosion may be masked
for long periods by technological advance,
particularly the use of fertilizers to
replace naturally occurring nutrients
carried away by erosion.
Erosion-induced losses of productivity
do not necessarily impose social costs.
Only those losses which impinge on
society's interest in maintaining the
productivity of the land are counted.
Society's interest does not necessarily
require zero losses. If future demands
on the land are expected to increase
little and technological advance to be
rapid, then productivity losses because
of erosion may be more than compen-
sated by technology. At present in the
United States, however, the prospect is
for substantial increase in demand for
products of the land and the pace of
technological advance shows signs of
faltering. In these circumstances,
prudence suggests that the effects of
erosion on productivity may give cause
for social concern.
On land that is not level, conservation
tillage reduces erosion 50 to 90 percent
compared with conventional tillage.
Conservation tillage thus has strong
advantages with respect to both water
quality and productivity.
Fertilizer
Excessive amounts of nitrates in
ground and surface water may harm
people and animals who drink the water
and nitrates and phosphorus can
stimulate plant growth in surface
waters, leading to accelerated eutrophi-
cation.
Most of the nitrogen and phosphorus
lost from farmers' fields is carried by
eroded soil. However, the soil nitrogen
is mineralized very slowly and so
contributes little to the nutrient enrich-
ment of the receiving waters. Much of
the phosphorus carried by eroded soil
also is not available to support plant
growth. For these reasons, the advantage
of conservation tillage in reducing
erosion does not convey a proportional
advantage in reducing nutrient lossesto
water bodies. Indeed, it may convey no
advantage at all.
The nitrate concentration in run-off
water generally is higher with conserva-
tion tillage because the technology does
not incorporate fertilizers as deeply as
conventional tillage and nutrients are
leached from the surface residues. The
amount of runoff is less with conserva-
tion tillage, however, so the increased
concentration of nitrates does not
necessarily mean greater loss of nitrates.
Leaching of nitrates to groundwater
typically is greater with conservation
tillage than with conventional tillage.
However, there is little basis for
generalizing about the differences
between the two technologies with
respect to delivery of nutrients to
surface waters.
Pesticides
Most pesticides show a strong affinity
for soil. Consequently, pesticide concen-
trations in eroded soil are usually higher
than in the associated runoff. Some of
the most commonly used pesticides,
with high toxicity to aquatic life —
trifluralin, endrin, and toxaphene — are
so tightly bound to the soil that a
reduction in erosion reduces the amounts
of these materials leaving the farmer's
field. This is true also of the herbicide,
paraquat. For other less insoluble
pesticides the bulk of losses are in
runoff, even though the concentration
of these materials in sediment is higher
than in runoff. The reason is that water,
by weight, is much the greater part of
water plus soil. For these more soluble
pesticides tillage practices which reduce
erosion but not runoff will not signifi-
cantly reduce pesticide losses. However,
as noted earlier, conservation tillage
typically reduces runoff as well as
erosion.
Apart from these effects on water
quality, the fact that conservation tillage
typically uses more herbicides per acre
than conventional tillage raises the
possibility of a difference in environ-
mental impact. Herbicide drift sometimes
damages neighboring crops, and it is
plausible to believe that the risk of this is
greater with conservation tillage simply
because more herbicides are applied.
Research on the effects of herbicides
on soil microorganisms indicates that
populations may be reduced immediately
after application, but they recover
quickly and no permanent damage is
done to important functions, e.g.
biological fixation of nitrogen. However,
not all possible avenues of damage to
soil microorganisms by prolonged use of
herbicides have been explored. Additional
research to explore these avenues is
needed.
Herbicides generally have low toxicity
to humans. A number are under suspi-
cion of being carcinogenic or mutagenic,
but the evidence is quite inconclusive.
On balance the greater reliance of
conservation tillage on herbicides
probably makes the technology a
greater threat to the environment than
conventional tillage, so far as pesticide
damage is concerned. The extent of the
increased threat is not known, but
present evidence suggests it is not
large.
The Future Spread of
Conservation Tillage
The economic advantages of conser-
vation tillage indicate that it could
eventually occupy 50 to 60 percent of
the Nation's cropland. Public policy
could either increase or decrease that
percentage. If erosion is perceived to be
a major threat to water quality and
productivity of the land, then policies
likely will be adopted to encourage the
spread of conservation tillage beyond
where economics alone would take it. If
the increased use of herbicides, however,
seems to pose a greater environmental
threat than erosion, policies to impede
the spread of conservation tillage would
be likely.
If the demand for cropland increases
60 to 70 million acres by 2010, as
present trends in crop demand and
yields imply, erosion likely will emerge
as a major national concern. Unless
research demonstrates that greatly
increased use of herbicides would
impose an even greater environmental
threat than erosion, policies likely will
be adopted to encourage the spread of
conservation tillage. In the absence of
more incriminating evidence against
herbicides than now is available, the
conclusion that 50 to 60 percent of
cropland eventually could be in conser-
vation tillage probably is conservative.
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Pierre Crosson is with Resources for the Future, Washington, DC 20036.
G. W. Bailey is the EPA Project Officer (see below).
The complete report, entitled "Conservation Tillage and Conventional Tillage: A
Comparative Assessment," (Order No. PB 82-249 160; Cost: $10.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protect/on Agency
Athens, GA 30613
•&U. S. GOVERNMENT PRINTING OFFICE: 1982/559-092/0506
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United States
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Agency
Center for Environmental Research
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