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Reducing Tillage
the crying need is for a soil surface similar
to that which we find in nature. [and] the way to
attain it is to use an implement that is incapable of burying
the trash it encounters; in other words,
any implement except the plow.
E.H. Faulkner, 1943
Although tillage is an ancient practice, the question
of which tillage system is most appropriate for any particular field
or farm is still difficult to answer. Before we discuss different
tillage systems, let's consider why people started tilling ground.
Intensive, full-field tillage was first practiced by farmers who
grew small-grain crops, such as wheat, rye and barley, primarily
in Western Asia, Europe, and Northern Africa. Tillage was needed
to control weeds and give the crop a head-start before a new flush
of weeds germinated. It also stimulated mineralization of organic
forms of nitrogen to forms that plants could use. Mostly, however,
intensive tillage created a fine seedbed, thereby greatly improving
germination. The soil was typically loosened by plowing and then
dragged to pulverize the clods and create a finely aggregated and
smooth seedbed. The loosened soil also tended to provide a more
favorable rooting environment, facilitating seedling survival and
plant growth. From early on, animal traction was employed to accomplish
this arduous task. At the end of the growing season, the entire
crop was harvested, because the straw also had considerable economic
value for animal bedding, roofing thatch, and brick making. Sometimes,
fields were burned after crop harvest to remove remaining crop residues
and to control pests. Although this tillage-cropping system lasted
for a long time, it resulted in excessive erosion, especially in
the Mediterranean region, where it caused extensive soil degradation.
Eventually deserts spread as the climate became drier.
Other ancient agricultural systems, notably those
in the Americas, did not use intensive full-field tillage for grain
production. Instead, they used a hoe for manual tillage that created
small mounds (hilling). This was well adapted to the regional staples
of corn and beans, which have larger seeds and require lower planting
densities than wheat, rye, and barley. Several seeds were placed
in a small hill, often with the help of a planting stick, and hills
were spaced several feet apart. In many, but not all cases, the
hills were elevated to provide a temperature and moisture advantage
to the crop. Compared with the cereal-based systems growing only
one crop in a monoculture, these fields often included two or three
plant species growing at the same time. This hilling system was
generally less prone to erosion than whole-field tillage, but climate
and soil conditions on steep slopes still frequently caused considerable
soil degradation.
A third tillage system was practiced as part of the
rice-growing cultures in southern and eastern Asia. Here, paddies
were tilled to control weeds, puddle the soil, and create a dense
layer that limited the downward losses of water through the soil.
The puddling process occurred when the soil was worked while wet
in the plastic or liquid consistency state and was specifically
aimed at destroying soil structure. This system was designed because
rice plants thrive under flooded conditions. There is little soil
erosion, because paddy rice must be grown either on flat or terraced
lands and runoff is controlled as part of the process of growing
the crop.
Full-field tillage systems became more widespread
as the influence of European culture expanded into other regions
of the world. It's better adapted to mechanized agriculture so the
traditional "hill crops" eventually became row crops.
The invention of the moldboard plow provided a more effective tool
for weed control by fully turning under crop residues, growing weeds,
and weed seeds. The development of increasingly powerful and comfortable
tractors made tillage an easier task. In fact, it has become almost
a recreational activity for some farmers.
New technologies have lessened the need for tillage.
The development of herbicides reduced the need for tillage as a
weed control method. New planters achieved better seed placement,
even without preparing a seedbed beforehand. Amendments, such as
fertilizers and liquid manures, can be directly injected or band-applied.
Now, there are even vegetable transplanters that provide good soil-root
contact in reduced or no-till systems. Although herbicides often
are used to kill cover crops before planting the main crop, farmers
and researchers have found that they can obtain fairly good cover
crop control through well-timed mowing, rolling, or rolling/chopping
greatly reducing the amount of herbicide needed.
Technologies have lessened
the need for tillage
- herbicides
- new planters and transplanters
- new physical methods for cover
crop suppression
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Increased mechanization, intensive tillage, and erosion have degraded
many agricultural soils to such an extent that people think they
require tillage to provide temporary relief from compaction. As
aggregates are destroyed, crusting and compaction create a soil
"addicted" to tillage. Except perhaps for organic crop
production systems, where tillage is needed because herbicides aren't
used, a crop can be produced with limited or no tillage with the
same economic return as conventional tillage systems. Managing soil
in the right way to make reduced tillage systems successful, however,
remains a considerable challenge.
Tillage Systems
Tillage systems are often classified by the amount
of surface residue left on the soil surface. Conservation tillage
systems are those that leave more than 30 percent of the soil surface
covered with crop residue. This is considered to be a level at which
erosion is significantly reduced (see figure 15.1). Of course, this
partially depends on the amount of residue left after harvest, which
may vary greatly among crops and harvest method (for example, corn
harvested for grain or silage). Although surface residue cover greatly
influences erosion potential, the sole focus on it is somewhat misleading.
Erosion potential also is affected by factors such as surface roughness
and soil loosening. Another distinction of tillage systems is whether
they are full-field systems or restricted tillage
systems (figure 15.2). The benefits and limitations of various tillage
systems are compared in table 15.1.
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Figure 15.1 Soil erosion
dramatically decreases with increasing surface cover. (Fall
plow (FP), fall chisel (FC), no-till (NT), corn = circles, soybeans
= no circles). Modified from Manuring, 1979. |
Conventional Tillage
A full-field system manages the soil uniformly across the entire
field surface. It typically involves a primary pass to loosen the
soil and incorporate materials at the surface (fertilizers, amendments,
weeds, etc.), followed by one or more secondary tillage passes to
create a suitable seedbed. Primary tillage tools are generally moldboard
plows, chisels, and disks, while secondary tillage is accomplished
with finishing disks, tine or tooth harrows, rollers, packers, drags,
etc. These tillage systems create a uniform and often finely aggregated
seedbed over the entire surface of the field. Such systems appear
to perform well because they create near-ideal conditions for seed
germination and crop establishment.
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a |
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b |
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c |
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d
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Figure 15.2 Four tillage
systems.
a) Chisel tillage: Shanks provide full-field
soil loosening.
b) No-till: Corn was directly planted into untilled soil.
Photo by NRCS.
c) Zone tillage: Planter loosens soil in the row and moves
residues to the side.
d) Ridge tillage: Crop is planted into small ridges without
tillage. |
Moldboard plowing is generally the least desirable practice because
it is energy intensive, leaves very little residue on the surface,
and often requires multiple secondary tillage passes. It also tends
to create plow pans. However, it is generally the most reliable
practice and almost always results in reasonable crop growth. Chisel
implements generally provide results similar to the moldboard plow,
but require less energy and leave significantly more residue on
the surface. Chisels also allow for more flexibility in depth of
tillage, generally from 5 to 12 inches, with some tools specifically
designed to go deeper. Disks usually perform shallow tillage, depending
on their size, and still leave residue on the surface. They can
be used as both primary and secondary tillage tools.
Although full-field tillage systems have their disadvantages,
they often can help overcome certain problems, such as compaction
and high weed pressures. Organic farmers often use moldboard plowing
as a necessity to provide adequate weed control and facilitate nitrogen
release from incorporated legumes. Livestock-based farms often use
a plow to incorporate manure and to help make rotation transitions
from sod crops to row crops.
Besides incorporating surface residue, full-field
tillage systems with intensive secondary tillage crush the natural
soil aggregates. The pulverized soil does not take heavy rainfall
well. The lack of surface residue causes sealing at the surface,
which generates runoff and erosion and creates hard crusts after
drying. Also, intensively tilled soil will settle after some rainfall
and may "hardset" upon drying, thereby restricting root
growth.
Full-field tillage systems can be improved by using
tools, such as chisels (figure 15.2a), that leave some residue on
the surface. Reducing secondary tillage also helps decrease negative
aspects of full-field tillage. Compacted soils tend to till up cloddy
and intensive harrowing and packing is then seen as necessary to
create a good seedbed. This creates a vicious cycle of further soil
degradation with intensive tillage. Secondary tillage often can
be reduced through the use of state-of-the-art planters, which create
a finely aggregated zone around the seed without requiring the entire
soil width to be pulverized. Indeed, a good planter is perhaps the
most important secondary tillage tool, because it helps overcome
poor soil-seed contact without destroying surface aggregates over
the entire field. A fringe benefit of reduced secondary tillage
is that rougher soil has much higher water infiltration rates and
reduces problems with settling and hardsetting after rains. Weed
seed germination is also generally reduced, but pre-emergence herbicides
tend to be less effective than with smooth seedbeds. Reducing secondary
tillage may, therefore, require emphasis on post-emergence weed
control.
Restricted Tillage Systems
These systems are based on the idea that tillage can be limited
to the area around the plant row and does not have to disturb the
entire field. Three tillage systems fit this concept no-till, zone-till,
and ridge-till.
The no-till system (figure 15.2b) does not involve
any soil loosening, except for a very narrow and shallow area immediately
around the seed zone. This localized disturbance is typically accomplished
with a fluted, or ripple, coulter on a planter. This is the most
extreme change from conventional tillage.
No-till systems have been used successfully on many
soils in different climates. They are especially well adapted to
coarse-textured soils (sands and gravels), as they tend to be softer
and less susceptible to compaction. It typically takes a few years
for no-tilled soils to improve, after which no-till crops often
out-yield crops grown with conventional tillage. The quality of
no-tilled soils, by almost any measure, improves over time. The
maintenance of surface residue protects against erosion and increases
biological activity by protecting the soil from temperature and
heat extremes. Surface residues also reduce water evaporation, which
combined with deeper rooting reduces the susceptibility to drought.
Another system, usually called zone tillage (figure
15.2c), gets some of the benefits of soil disturbance in the soil
around the plant row without disturbing the entire field. It uses
multiple fluted coulters mounted on the front of a planter (figure
15.3) to develop a fine seedbed of approximately 6 inches wide by
4 inches deep, and typically uses trash wheels to move residue away
from the row. The system may also include a separate pass of a "zone
building" implement during the off season (see figure 14.1).
This typically involves a narrow shank or knife, sometimes used
to inject fertilizers, combined with a trash remover or hilling
disk (to perform in-row tillage and overcome compaction problems).
The term "strip tillage" often is used to describe the
latter system.
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Figure 15.3 Zone-till planter.
a. Coulters (cut up residues and break up soil in seed zone);
b. Ferti-lizer disc openers (place granular starter fertilizer
in a band next to the seed); c. Spider (trash) wheels (move
residue away from the row); d. Seed place-ment unit; e. Press
wheels (create firm seedbed); and f. Wheel used for transporting
the planter. |
Ridge tillage (figure 15.2d) combines some tillage
with a ridging operation. This system is particularly attractive
for cold and wet soils, because the ridges offer developing plants
a warmer and better-drained environment. The ridging operation can
be combined with mechanical weed control and allows for band application
of herbicides. This decreases the cost of chemical weed control,
allowing for about a two-thirds reduction in herbicide use.
For fine and medium-textured soils, zone and ridge
tillage systems generally work better than strict no-till, especially
in regions with cold and wet springs. Because these soils are more
susceptible to compaction, some soil disturbance is probably beneficial.
No-till is used successfully for narrow-row crops, including small
grains, perennial legumes and grasses. Zone and ridge tillage are
only adapted to wide-row crops with 30-inch spacing or more.
Which tillage system for your farm?
This is difficult to answer. It depends on your climate,
soils, cropping systems, and your objectives. Here are some general
guidelines.
Grain and vegetable farms have great flexibility with
adopting reduced tillage systems. In the long run, limited disturbance
and residue cover improve soil quality, reduce erosion, and boost
yields. A negative aspect of these systems is that, at first, they
may require more herbicides. However, combining reduced tillage
with use of cover crops frequently helps reduce weed problems. Weed
pressures typically decrease significantly after a few years. Mulched
cover crops, as well as newly designed mechanical cultivators, help
provide effective weed control in high-residue systems. Some innovative
farmers use no-till combined with a cover crop, which is mowed or
otherwise killed to create a thick mulch. Steve Groff, a vegetable
and field crop farmer in Pennsylvania, modified a rolling stalk
chopper to roll down and crimp his vetch/rye cover crop, providing
weed control with minimal use of herbicides (see profile).
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Figure 15.4 No-till transplanting
of vegetables into a killed cover crop on the Groff farm in
Pennsylvania. Photo by Ray Weil. |
Farmers need to be aware of potential soil compaction problems with
reduced tillage. If a strict no-till system is used on a compacted
soil, especially on medium or fine-textured soils, serious yield
reductions may occur. As discussed in chapter
6, dense soils have a narrow water range for which plant growth
is not restricted. Crops growing on compacted soils are more susceptible
to inadequate aeration during wet periods and restricted root growth
and inadequate moisture during drier periods. Compaction, therefore,
reduces plant growth and makes crops more susceptible to pest pressures.
In poorly structured soils, tools like zone-builders
and zone-till planters may provide compaction relief in the row,
while maintaining an undisturbed soil surface. Over time, soil structure
improves, unless recompaction occurs from other field operations.
Crops grown on imperfectly drained soils tend to benefit greatly
from ridging or bedding, because part of the root zone remains aerobic
during wet periods. These systems also use controlled traffic lanes,
which greatly reduce compaction problems. Unfortunately, matching
wheel spacing and tire width for planting and harvesting equipment
is not always an easy task.
Before Converting
to No-Till
An Ohio farmer asked one of the authors what
could be done about a compacted, low organic matter, and low
fertility field that had been converted to no-till a few years
before.
Clearly, the soil's organic matter and nutrient levels should
have been increased and the compaction alleviated before the
change. Once you're committed to no-till, you've lost the
opportunity to easily and rapidly change the soil's fertility
or physical properties. The recommendation is really the same
as for someone establishing a perennial crop like an apple
orchard. Build up the soil and remedy compaction problems
before converting to no-till. It's going to be much harder
to do later on.
Once in no-till, there are some things that can be tried to
break up compacted soils, such as a sorghum-sudangrass cover
crop. However, a severe compaction problem may require tilling
up the soil and starting over. |
For organic farms, as with traditional farms before agrichemicals
were available, full-field tillage may be necessary for mechanical
weed control and incorporation of manures and composts. Organic
farming on lands prone to erosion may, therefore, involve tradeoffs.
Erosion can be reduced by using rotations with perennial crops and
a modern planter to establish good crop stands without excessive
secondary tillage. In addition, soil structure may be easier to
maintain, because organic farms generally use more organic inputs,
such as manures and composts.
Livestock-based farms face special challenges related
to applying manures or composts to the soil. Although these materials
may sometimes be injected directly, some type of tillage usually
is needed to avoid large losses of nitrogen by volatilization and
phosphorus and pathogens by runoff. Transitions from sod to row
crops are usually easier with some tillage. Farmers raising livestock
should try to reduce tillage as much as possible and use methods
that leave residue on the surface.
Rotate Tillage Systems?
A tillage program does not need to be rigid. When
changing to reduced tillage, consider incorporating nutrients and
organic matter with the moldboard plow (see box on p. 142). Fields
that are zone or no-tilled may occasionally need a full-field tillage
pass to provide compaction relief or to incorporate amendments.
Tilling a no-till or zone-till field should be done only if clearly
needed. Although a flexible tillage program offers a number of benefits,
aggressive tillage with a moldboard plow and harrows on soils for
which no-till is best adapted will destroy the favorable soil structure
built up by years of no-till management.
Timing of Field Operations
The success of a tillage system depends on many other
factors. For example, reduced tillage systems, especially in the
early transition years, may require more attention to nitrogen management,
as well as weed, insect, and disease control. Also, the performance
of tillage systems may be affected by the timing of field operations.
If tillage or planting is done when the soil is too wet (its water
content is above the plastic limit) then cloddiness and poor seed
placement may result in poor stands. Tillage also is not recommended
when soil is too dry, because of excess dust creation, especially
on compacted soils. A "ball test" (Chapter
6) helps ensure that field conditions are right.
Frost Tillage?
You may have heard of frost seeding legumes
into a pasture, hayfield, or winter wheat crop in very early
spring, but probably never heard of tilling a frozen soil.
It seems a strange concept, but some farmers are using frost
tillage as a way to be timely and reduce unintended tillage
damage. It can be done after frost has first entered the soil,
but before it has penetrated more than 4 inches. Water moves
upward to the freezing front and the soil underneath dries.
This makes it tillable as long as the frost layer is not too
thick. Compaction is reduced because equipment is supported
by the frozen layer. The resulting rough surface is favorable
for water infiltration and runoff prevention. Some livestock
farmers like frost tillage as a way to incorporate or inject
manure in the winter. |
Optimum Tillage
System
New agricultural technologies provide opportunities
to reduce tillage and improve soil quality. The optimum system
for any farm depends mainly on soils and climate, as well
as the need for mechanical weed control, incorporation of
cover crops and animal manures, and lessening compaction.
Tillage systems should change in the direction of those that
leave residue and mulches on the surface and that limit the
pulverization of soil aggregates. |
Because soil compaction may affect the success of
a reduced tillage system, a whole-system approach to soil management
is needed. For example, no-till systems that also involve harvesting
operations with heavy equipment will succeed only if traffic can
be restricted to dry conditions or fixed lanes within the field.
Even zone-tillage methods may fail if heavy harvest equipment is
used without fixed lanes. Soils that are severely eroded and low
in organic matter may need careful management when making the transition
to reduced tillage systems. In such cases, methods that increase
the soil organic matter content and improve soil structure (for
example, cover cropping and organic amendments) before reducing
tillage will improve the probability for success of these systems.
As surface residue levels increase with the start of reduced tillage,
some soil loosening may be needed to relieve compaction.
Sources
Cornell Recommendations for Integrated Field Crop Production.
2000. Cornell Cooperative Extension, Ithaca, NY.
Manuring. 1979. Cooperative Extension Service
Publication AY-222, Purdue University. West Lafayette, IN.
Ontario Ministry of Agriculture, Food, and Rural Affairs.
1997. No-till: Making it Work. Available from the Ontario
Federation of Agriculture, Toronto, Ontario (Canada).
van Es, H.M., A.T. DeGaetano, and D.S. Wilks. 1998.
Upscaling plot-based research information: Frost tillage. Nutrient
Cycling in Agroecosystems. 50: 8590.
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