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Introduction
This publication takes a brief look at conservation
tillage as it may be applied to organic cropping systems. A number
of the most promising strategies and technologies are described, and
abstracts of recent research are provided. The focus is on annual
cropping systems. Both agronomic and vegetable cropping systems are
discussed.
Very little no-till/low-till research has been
done under conditions typically found on organic farms. To achieve
a true organic context for a research trial, it is not enough simply
to avoid the use of prohibited fertilizers and pesticides. The fields
on which the trial is conducted should be certified, or be close to
certifiable, as organic. In this way, the real-world conditions of
an organic farm—conditions
that follow from crop rotation, natural nitrogen cycling, lack of
herbicide carryover, enhanced beneficial populations, and so on—can
have their effect on the outcome of the trial. These factors can make
a big difference in how a system performs over time when a new practice
or product is tested.
At present, the amount of research being done
that meets organic criteria is very small, and only a tiny portion
deals with conservation tillage. We have had to cast a wider net and
review—in
addition to the few organic studies—a
considerable volume of conventional research, to find applications
that might be adaptable to organic farming. This was challenging because
"adaptability" was not always readily apparent. The use
of herbicides and commercial fertilizers in conventional crop production—especially
no-till—is
a given, and mention might not be made in articles and reports. Depending
on how and when such inputs are used, they can make a vast difference
in predicting how a practice might work in an organic context.
Making conservation tillage work in organic
systems is, apparently, not easy. Many of the approaches discussed
are clearly not "field ready." More research is definitely
needed. Also, a high degree of sophistication will be necessary on
the part of the farmer, which leads to an interesting observation.
The pursuit of no-till/low-till organic systems clearly bucks the
"dumbing-down" trend in conventional crop farming. It contrasts
with commercial packaging of genetically engineered crops and over-the-top
herbicides that minimizes skill and knowledge required at the farm
level.
Make no mistake, conventional crop production is not lacking in information
or skill. Most of that knowledge, however, resides with the researchers,
technicians, advisors, and sales persons involved in developing and
delivering technology to the grower. The farmer's role increasingly
resembles that of a production line worker who is simply told what
to do and when. This is in stark contrast to traditional farming,
where the skill and knowledge base resides mainly in the head of the
farmer, and demands much of him or her as scientist, artist, and manager.
Without a doubt, the pursuit of conservation
tillage by organic farmers and researchers is a very good thing. It
is consistent with the compelling need for more sustainable technologies
within organic farming, and the wider trend towards environmental
conservation in all of agriculture.
Return
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Organic
Farming & the Tillage Dilemma
In the first half of the 20th century, clean
tillage was such an integral part of mainstream American agriculture
that no qualification or explanation was necessary. If you farmed,
you plowed to break the sod, typically using either a moldboard or
disc plow that inverted the soil cover, leaving virtually no plant
material on the surface. This was usually followed by harrowing several
times to create a seedbed, frequent cultivations to control weeds
in the growing crop (in row crops), and plowing again to bury residues
and re-start the cycle.
As herbicide use became widespread, the importance
of some tillage operations—especially
post-planting weed cultivations—began
to decline. Organic farmers, and some others who chose not to use
herbicides, continued to cultivate their crops using steel and flame.
However, one thing common to both the organic and conventional farmers
at mid-century was that both had a lot of bare soil between the seasons
and between the rows.
Bare soil, whether left exposed by tillage
or by herbicide, means potential for wind and water erosion, nutrient
leaching, reduced biological diversity, loss of organic matter, and
further challenges to the sustainability of farming. These downsides
of clean tillage were not so much denied as they were simply accepted
as the necessary costs of crop agriculture. Even to those concerned
with conservation, other options were not readily apparent. This viewpoint
began to change around 1960.
Inspired in part by Edward Faulkner's 1943
classic book Plowman's Folly (1)—a
critique of moldboard-plow tillage—researchers
in the '60s started taking a serious look at tillage alternatives
that not only reduced the number of field operations, but left a crop
residue mulch on the soil surface. Expectations were modest at first,
but soon agronomists and farmers began envisioning productive cropping
systems with a perpetual cover of living and/or decaying vegetation.
With that sort of soil protection, most of the soil and environmental
damage done by clean tillage might be halted and even reversed. Erosion-prone
slopes might be cropped indefinitely.
To visionaries of that era, herbicides were
the technological key to making such systems a reality. Herbicides
had already made many cultivation operations appear to be optional
and even obsolete in clean-tillage farming. It was logical to assume
that they could be used to eliminate tillage operations entirely.
Soon, a considerable body of low-till and no-till
information and technologies emerged, the bulk of it centering on
the use of pesticides. The trend has continued up to the present.
And now, as more and more environmental problems are being laid at
the feet of agriculture, the accelerating trend towards conservation
tillage—along
with the requisite pesticide technology—is
being used as an image-builder for modern farming.
Some
Benefits of Conservation Tillage
|
- reduced
wind erosion
- reduced
water erosion
- erodible
land brought into production
- increased
options for multiple cropping
- improved
soil moisture management
- flexible
timing for field operations
- improved
soil structure
- better
humus management
- moderation
of soil temperature
|
It has been taken for granted
by many that organic farming, which does not use herbicides, is
forever shackled to clean cultivation. This assumption has been
used disparagingly to characterize organic crop production as erosive
and environmentally destructive. This charge was bolstered when
the results of a long-term Midwestern study were published in the
journal Science in September 2000 (2).
The study contrasted the net global warming potential (GWP) of several
natural and agro-ecosystems. It looked at such factors as the release
of greenhouse gases CO2, CH4, and N2O,
sequestration of carbon as soil organic matter, and the use of CO2-generating
inputs like fertilizer, lime, and fuel.
All annual cropping systems,
including those with legume cover crops in rotation, increased GWP
to varying degrees. While the organic system scored considerably
better than the conventional tillage alternative, its net GWP was
still much higher than that of the no-till comparison. Clearly,
organic agriculture would benefit if no-till or low-till technologies
could be adapted. Advances in this area are now much further along
than many critics acknowledge.
Organic producers have long nurtured
an interest in conservation tillage. This was well documented in
the mid-1970s as part of the Washington University study of organic
agriculture in the Corn Belt. The researchers observed that the
vast majority of organic farmers taking part in the study were using
chisel plows rather than conventional moldboard plows. Chisel plowing
is a form of mulch tillage, in which residues are mixed in
the upper layers of the soil; a significant percentage remains on
the soil surface to reduce erosion. Some organic growers had adopted
ridge-tillage—another
conservation tillage system with even greater potential to reduce
erosion (3).
The ready adoption of these technologies stood in sharp contrast
to neighboring conventional farms of that time where there was,
as yet, little-to-no evidence of conservation tillage practices
being implemented.
The remainder of this publication
will describe some of the advances in no-till and low-till farming
pioneered by the USDA, land-grant universities, and farmers, with
an eye towards those currently used by organic producers or with
significant potential for use.
Return
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Mulch
Tillage
Mulch tillage has already been described as
a tillage system in which a significant portion of crop residue is
left on the soil surface to reduce erosion. It is usually accomplished
by substituting chisel plows, sweep cultivators, or disk harrows for
the moldboard plow or disk plow in primary tillage. This change in
implements is attractive to organic growers because residues are not
buried deep in the soil, and good aerobic decomposition is thus encouraged.
Of all the agronomic-scale options, mulch tillage is the most easily
adapted to organic management and is appropriate for most agronomic
and many horticultural crops. However, the additional environmental
benefits of mulch tillage are not as great as those possible with
other, more challenging approaches.
Return
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Ridge
Tillage
Ridge tillage is characterized by the maintenance
of permanent or semi-permanent ridge beds across the entire field.
It is primarily intended for the production of agronomic row crops
like corn, soybeans, cotton, sorghum, and sunflower. The ridge beds
are established and maintained through the use of specialized cultivators
and planters designed to work in heavy crop residues. In contrast
to most forms of mulch tillage, more crop residue remains on the soil
surface for a greater portion of the season. Additionally, when done
on contour, the ridges themselves largely supplant the need for larger
soil conservation structures like terraces on many fields.
Like mulch tillage, ridge tillage has proven
quite adaptable to organic management, particularly with improvements
in high-residue cultivation equipment. Some of the best documentation
of the challenges and potentials of ridge tillage in organic systems
was provided in the Nature's Ag School series. These publications—produced
by the Rodale-sponsored Regenerative Agriculture Association in the
late 1980s—focused on research done on the Richard Thompson farm in
Boone, Iowa. While these are now out of print, the Thompsons are producing
their own updated reports annually with assistance from the Wallace
Institute. The series, titled Alternatives in Agriculture,
continues to report on the Thompsons' research—much of it still focused
on ridge tillage and cover crops (4).
High-residue cultivation equipment appears to
be a key to making herbicide-free ridge tillage (and sometimes even
mulch tillage) function successfully, by allowing cultivation through
dense surface mulches. While there is considerable variation in equipment,
the typical features of high-residue cultivators are large coulters
followed by large sweeps mounted on single shanks. The coulters cut
through residue in the middle of the interrow area to assure that
the residue will not hang up on the sweep shanks. The sweeps are run
shallow, yet deep enough so that the flow of soil helps carry crop
residues over the sweep during cultivation. Furrowing wings are used
on the sweep to aid in rebuilding ridges.
For good, general information on mulch tillage,
ridge tillage, and conventional no-till systems, the Conservation
Technology Information Center (5)
is a good place to begin. An excellent basic text that compares these
and other tillage systems is Conservation Tillage Systems and Management:
Crop Residue Management with No-till, Ridge-till, Mulch-till, and
Strip-till, which was revised and expanded in 2000 (6).
Return
to "Contents"
Killed
Mulch Systems
Advances in cover crop research have generated
some innovative approaches to conservation tillage that show great
potential for organic conservation tillage. Systems are now evolving
centered on the concept of growing a dense cover crop, killing it,
and planting or transplanting into the residue. The dense biomass
provided by the killed cover crop not only protects and builds the
soil, it also provides substantial weed suppression. On a small scale,
organic gardeners have long relied on dense mulches as an alternative
to hoeing and cultivation for weed management. Killed mulch systems
are an attempt to capture the benefits of that practice on a larger
scale.
In conventional conservation tillage, herbicides
are primary tools for killing cover crops. The non-chemical alternatives
being tried for organic systems include a number of mechanical implements
and weather stress. The mechanical technologies currently being explored
include mowing, undercutting, rolling, and roll-chopping.
Mowing
Several mowing technologies are in common use
on mechanized farms. These include sickle bars, rotary (bushhog),
flail, and disc mowers. Each has different characteristics that affects
its utility in creating a suitable mulch.
Sickle bar mowers have been fairly effective.
Sickles cut close to the soil surface, increasing the chances of a
good kill; they also lay the cover down uniformly over the soil surface—an
important characteristic in weed suppression. As a further advantage,
sickle mowing does not chop up the cover crop. The major problem with
this technology is encountered when mowing viney legumes like hairy
vetch or field peas. The vines easily get hung up on the machine,
slowing field operations and leaving a very uneven mulch. Researchers
speculate that a reel-assisted sickle bar—such as a mower-conditioner—would
probably work better if it can be modified to not create a windrow
(7).
Disc mowers do a good job of cutting viney crops
and mow close to the soil surface. However, the resulting mulch layer
is uneven and bare strips are frequently left. Rotary mowing is perhaps
the least suitable option. Rotary mowers do not cut as low as sickle
bars. They distribute the mulch unevenly and chop it up so that decomposition
is rapid and soil coverage is short-term.
Flail mowing appears to be the preferred technology
at present. It cuts low and leaves an even layer of residue. However,
it also chops the biomass quite finely, leading to rapid breakdown
and short-term coverage (7).
Timing is important when mowing. Rye is most
effectively mow-killed at flowering. If mowing is done earlier, the
plant re-grows readily. Optimum control of hairy vetch is managed
when mowing is done at mid-bloom or later, though stem length appears
to be a more important factor; the greater the stem length at mowing,
the easier the kill.
Mowing has several advantages. It is less dependent
on soil moisture conditions than mechanical methods like undercutting
that involve some tillage. It can also be done at relatively fast
field speeds and involves the use of commercially available equipment
that requires little to no modification.
Undercutting
Undercutting is not a new concept. V-blade field
cultivators have long been used in the western states to control weeds
for summer fallow by severing the plants below the crown and leaving
the residue on the soil surface. They were especially popular in the
1940s and 1950s. There has been a resurgence in their use among organic
growers since the late 1980s.
Much attention is now being given to an adaptation
of the traditional undercutting concept. It entails the use of specialized
equipment that both severs the roots of the cover crop and flattens
the biomass on the surface of the soil. The unit is primarily suited
to bed production systems. Originally designed by Nancy Creamer and
fellow researchers at Ohio State, the undercutter features a large
blade or blades (adapted from a V-blade plow) that are run just under
the surface of the soil to cut cover crops off just below the crown.
A rolling basket is positioned to the rear of the blades for depth
adjustment and to flatten the severed cover crop.
The undercutter has proved successful in killing
a variety of winter annual cover crops including rye, hairy vetch,
bigflower vetch, crimson clover, barley, and subterranean clover.
Kill was most effective when these were allowed to reach mid-bloom
or later. Undercutting is much less successful at killing biennial
and perennial species such as red clover, ladino clover, sweetclover,
fescue, orchardgrass, and perennial ryegrass (8).
Undercutting is also effective for killing a
variety of spring and summer annual cover crop species including soybean,
buckwheat, lentil, German foxtail millet, and Japanese millet, sesbania,
and lab lab. It is less successful with cowpeas, pearl millet, sudangrass
and sorghum-sudangrass (9).
A big advantage of the undercutter (and the
V-blade) is that it achieves a good kill while not chopping the cover
crop, resulting in a more persistent, weed-suppresive mulch. It also
loosens the soil, which makes for easier transplanting. The undercutter
is somewhat limited, however, if soil moisture levels are high. Soil
type can also be a limitation. University researcher Jeff Mitchell
observed poor performance with undercutting in the heavy clay soils
he works with in California (10).
Though the V-blade or Noble plow is still widely
available in the West, the bed-style undercutters are not commercially
available and must be home-built. Ample detail on construction is
provided in a 1995 article by Nancy Creamer, published in the American
Journal of Alternative Agriculture (8).
For those with access to back issues of The New Farm (once
published by the Rodale Institute), the July-August 1994 issue featured
a good picture on page 31 along with some enlightening text (11).
Rolling
& Roll-Chopping
Rolling is essentially mechanical lodging. Implements
are used to bend or break the plant stems and press them uniformly
against the soil surface. The kinds of equipment used for rolling
are surprisingly varied. The most recognizable are field rollers;
turf or construction rollers can also be used. A modified version
of these basic rollers features angle-iron bars welded horizontally
along the length of the roller. This adds a crimping action for better
kill. Similar rolling action can be achieved using cultipackers or
similar implements.
Rolling can also be done using a grain drill
with closely spaced cutting coulters and cast-iron press wheels. In
addition to lodging the crop, this implement also kills by cutting
the cover crop stems and leaves. Another piece of equipment that has
been employed is a flail mower with the power disengaged. The roller
gauge wheel apparently serves the purpose. One of the big advantages
of rolling is that suitable equipment can usually be found on the
farm and easily adapted (12).
In North Carolina research trials, rolling was
the least successful means of killing a range of summer cover crops,
when compared to mowing and undercutting (8).
According to Virginia Tech's Ronald Morse, it is the least physically
damaging to the cover crop and, therefore, is the least effective
overall. However, he does not consider this a significant disadvantage
where mechanical transplanting is used. The passage of the transplanter
itself further damages the cover crop to the point where competition
with the crop is nil and the benefits of a slow-decomposing, non-chopped
mulch can be realized (12)
Roll-chopping involves the use of specialized
equipment that is commecially available. Rolling stalk choppers—such
as those marketed under the trade name Buffalo—cut the cover
crop stems perpendicular to the direction of travel. Roll-chopping
has gained considerable visibility among no-till/low-till investigators.
Several farmers have reported significant success, but stressed the
need for a more flexible design to handle conditions like raised beds
(13).
A significant advantage of both rolling and roll-chopping is that
they can be done at relatively fast field speeds.
Weather-Kill
The concept of weather-killing cover crops involves
the strategic planting of a cover crop that will be reliably killed
by temperature shifts as seasons change. It appears that the most
common strategies being researched involve the planting of summer
annual covers like forage sorghums, millet, cowpeas, buckwheat, berseem
clover, haybeans, or annual medic that are easily killed by even mild
winter freezes, while leaving a dense mulch. Planting or transplanting
of early spring crops can follow after mowing and/or strip tillage.
Among the benefits of such winter-kill systems is that they offer
a good opportunity for extending killed-mulch options to early spring
crops. Attempts to kill winter annuals at early growth stages have
not worked well. More importantly, most winter annuals have not produced
sufficient biomass by early spring to offer much weed suppression.
Winter-killed mulches cease transpiration as
soon as they are killed. In dryer climates this is an advantage due
to reduced soil moisture depletion. In wetter climates, however, a
living cover crop would help remove excess water and allow earlier
field operations. Moisture conditions play an important role in the
viability of a winter-kill system. A late-summer or early-fall drought
can result in a poor cover crop going into the winter and much too
little biomass for weed suppression.
Cover
Crops for Killed Mulch Systems
In general, cover crop selection in killed mulch
systems should favor dense, tall-growing species in wetter climates
and water-use efficient species in drier climates. In either case,
the crop should be easily killed and leave considerable biomass. Research
appears to concentrate most often on the winter annuals hairy vetch,
grain rye, and winter peas. In this same category is black medic—in
northern climates a short-lived perennial that reseeds itself annually.
Where summer annuals are needed, research seems focused on soybeans,
forage sorghums, and, to a lesser degree, on buckwheat.
Combining cover crop species—a legume with a
grass—is often noted as a good strategy. Nitrogen fixation from the
legume can be optimized, a maximum level of biomass is usually produced,
and the carbon-to-nitrogen ratio of the mulch is generally in a range
that releases nitrogen to the crop at a desirable rate (9).
In the case of winter cover crops, combinations are also desirable
because harsh conditions may eliminate one of the species. In such
instances, the survivor still succeeds in providing an acceptable
level of soil protection.
Particular interest has been shown in grain
rye. This is due not only to its winter hardiness and ability to generate
biomass, but also to its allelopathic characteristics. Rye produces
chemicals that inhibit the germination and growth of a large number
of broadleaf and grassy weeds. These chemicals, along with their breakdown
products, continue to be active as rye residue decays on the soil
surface, making it an especially effective weed suppressant (14).
Rye is not the only cover crop with allelopathic
characteristics; other grasses like oats also exhibit some allelopathy.
Researchers are also investigating various brassica species such as
rape and mustard, though most studies have looked into the effects
of soil-incorporated residues (15,
16).
While brassicas do provide some weed suppression through allelopathy,
they will likely do best in combination with another cover crop capable
of producing more biomass. It should be noted that allelopathy is
a two-edged sword. Crops, too, can be damaged and researchers are
working to determine which cover crops can be used safely with which
cash crops. Further research on this subject is discussed later in
the text.
The
Challenges of Killed Mulches
Most killed mulches do not provide thorough,
long-season weed control without some additional effort. Studies on
light penetration done in California found that even the densest of
killed mulches still allowed roughly 20% of sunlight to leak through
to the soil surface (10).
This percentage increases as the mulch layer decomposes and weeds
will begin to emerge. Some form of hoeing, cultivation, or both may
be needed later in the season.
High-residue cultivators have been tried in
such circumstances. Farmers report that they do work but may still
"hang up" in especially heavy, viney mulches (13).
Where weed problems are anticipated, and relatively early cultivations
are a certainty, it may be desirable to favor a killed mulching system
in which the biomass breaks down more rapidly to facilitate cultivation.
This would suggest flail mowing, for example, and the preference for
a legume or buckwheat cover crop that would decompose more rapidly
(17).
One strategy that is being used to improve stands is to shift from
direct seeding to the use of transplants. Transplanting can be done
somewhat later than direct seeding, allowing for greater warming of
the soil. It also assures a better stand and allows the crop a more
competitive jump on weeds (12).
Transplanting is somewhat limited, however, as it is not appropriate
for all crops. Another strategy that works to improve stands is zone
tillage. It will be discussed later on.
Resources
& Research on Killed Mulch Systems
The USDA has conducted some excellent research
on the use of killed mulches at its research station in Beltsville,
Maryland. Researchers Aref Abdul-Baki and John Teasdale have investigated
the (flail) mow-killing of a number of cover crops for no-till culture
of summer vegetables, particularly tomatoes. The results are well-detailed
in the USDA Farmers' Bulletin 2279 (18).
Note that page 8 of that bulletin features a picture of a homemade
crimper-roller also used to kill cover crops in their trials.
Later research by this USDA team has extended
into fall broccoli production (19,
20).
The mow-killed cover crops were, in this case, soybeans and millet.
The soybeans were a recent USDA release called Donegal, which
was bred for size, biomass production, and early growth. The reported
research was not done entirely within an organic context, as herbicides
were used in the establishment of the cover crop. However, it appears
it would still adapt well to an organic system.
Participating with Abdul-Baki and Teasdale in
the broccoli research was Dr. Ronald Morse, of Virginia Polytechnic,
who has led the way in development of no-till transplanting. Morse,
Abdul-Baki and Teasdale have also collaborated extensively with Pennsylvania
farmer Steve Groff, who has made great strides in no-till vegetable
production and farm diversification. Groff has brought particular
attention to the use of roll-chopping as a cover crop management technology.
Though his system is not organic, observations made in this system
should be relevant to organic management (21).
Dr. Morse has written a fine summary on the
art and science of no-till transplanting that also summarizes various
mulch-killing strategies. Especially notable is his description of
the subsurface tiller-transplanter (SST-T), which he worked to pioneer.
This tool is designed for transplanting into high-residue conditions
and is one of the most promising implements for making an organic
low-till system work. Dr. Morse's article, Keys to Successful Production
of Transplanted Crops in High-Residue, No-Till Farming Systems
is reprinted in the Proceedings of the 21st Annual Southern Conservation
Tillage Conference for Sustainable Agriculture (12).
One of the best summaries of technologies and research into the mechanical
killing of cover crops was co-authored by Nancy Creamer, with North
Carolina State University, and Seth Dabney, with USDA-ARS in Oxford,
Mississippi. Titled Killing Cover
Crops Mechanically: Review of Recent Literature and Assessment of
New Research Results
(7),
the article was published in 2002 in the American Journal
of Alternative Agriculture. Creamer and Dabney are among the
true pioneers in organic low-till and cover crop research for horticultural
crops.
The Kerr Center for Sustainable Agriculture
is currently funding some on-farm research on winter-killing cover
crops for vegetable systems in eastern Oklahoma. Twenty-four legume-and-grass
cover crop combinations are being evaluated. Assistance is being provided
by Oklahoma-based ARS personnel and Oklahoma State University researchers
and Extension (22).
Contact Alan Ware at the Kerr Center (23)
for more details.
Another New Farm article of particular
relevance to killed-mulch farming—in this instance, weather-kill—is
a 1993 piece by Bob Hofstetter titled Smother Crops (24).
The focus of the article is the planting of various cover crop species
out of season with the objective of their being killed by expected
weather extremes. The experience of Pennsylvania farmer Frank Pollock
with winter-killed oats is highlighted. This grower had successfully
grown both garlic and specialty potatoes with this cover crop system
for 10 years.
Return
to "Contents"
Living
Mulches
Living mulches represent another alternative
to low-till/no-till that organic agriculture must explore. In the
broadest sense, the term "living mulch" can apply to any
system in which an actively growing or dormant cover crop remains
in place as a companion to a commercial crop. As such, this concept
encompasses a number of practical and theoretical options. One of
the approaches that has generated a lot of interest in recent years
involves the interseeding of crops with low-growing smother crops
that suppress weeds and reduce erosion both during the growing season
and after the crop has been harvested. Interseeding may eliminate
one or more weed-controlling cultivations in an organic system. However,
it is not a strategy to reduce primary tillage and is less germane
to this publication. Our focus will be on living mulch practices that
involve the establishment of crops into living cover crops that are
not killed, but remain living for all or part of the cropping season.
Erosion control and reduced tillage are among
the main attractions that living mulches share with killed mulch systems.
A specific benefit of living mulch systems—insect pest suppression—has
also drawn attention. Living mulches frequently serve as beneficial
insect habitats, thus supporting a population of predators and parasites
that help keep crop pest numbers at manageable levels. For example,
Costello and Altieri demonstrated the habitat effect in the Salinas
Valley of California while growing broccoli in a living mulch of white
clover (25).
According to Leary and DeFrank (26),
successful living mulch systems manage a balance between weed suppression
and competition with the cash crop for light water and nutrients.
In a preferred system, the mulch would resume full dominance of the
agroecosystem following harvest—crowding out weeds, preventing erosion,
providing habitat, and building soil fertility. Even beginning to
approach such an ideal can be highly challenging.
One of the more obvious strategies for making
a living mulch system work entails supplementing cash crop nutrition
and moisture in a targeted way. Sidedress and foliar fertilization
strategies can be helpful here; especially promising is the use of
drip fertigation—supplying soluble organic fertilizers by injection
into the irrigation system. While feasible technically, such strategies
may or may not always be environmentally responsible or economical.
Most researchers investigating living mulches
are focusing on systems that achieve a balance between the living
mulch and the cash crop through:
1) selection of a compatible cover crop
2) some form of mulch suppression (usually dependent on careful
timing), and
3) a zone of tilled, weed-controlled seedbed (e.g., zone tillage)
through the early season.
Cover
Crop Selection for Living Mulches
A good living mulch is said to have four desirable
characteristics (27):
· rapid establishment to provide early weed and erosion control
· tolerance to field traffic
· tolerance to drought and low fertility
· low cost of maintenance
These characteristics are considerably different
from those desired for killed mulches, where tall, easily-killed annuals
typically predominate. Preferred living mulch species are typically
prostrate in growth habit and often perennial. Annual species, however,
can also be effective choices. Particular interest has been shown
in subterranean clover, or "subclover."
Subterranean clover is a self-seeding winter
annual with a prostrate growth habit. Well adapted throughout much
of the South, subclover is typically planted in the late summer or
fall. It grows vegetatively but is held dormant throughout much of
the winter. Flowering and seed development occur in late spring and
early summer. The plant then senesces and dies during the heat of
summer, leaving a dense vegetative mulch that is non-competitive with
the growing crop. The next generation of subclover arises from seed.
Like the peanut, subclover is geocarpic—its seed pod develops
at and below the surface of the soil. This assures soil-to-seed contact
and improves the chances for reviving the stand without tillage operations.
Ilnicki and Enache (28)
reported considerable success in New Jersey using subclover as a living
mulch in field corn, soybeans, and a number of vegetable crops. No
herbicides were used for mulch suppression, though mowing was tested.
The researchers noted that mowing subclover just prior to planting
improved the yields of some crops like sweet corn. It was believed
that mowing allowed earlier warm-up of the seedling bed, giving the
crop a better start.
Living
Mulch Suppression
In instances where a cover crop like subterranean
clover is used, some suppression is provided by the natural cycle
of the plant itself as it senesces and dies, or goes into seasonal
dormancy. Still, mowing has been shown to be beneficial, as previously
pointed out. Most living mulches require some form of suppression
during the cropping season. In conventional systems, it is not uncommon
to use sub-lethal applications of herbicide for this purpose. Two
mechanical means of suppression that are suited to organic systems
are mowing and partial rototilling.
Mowing appears to be the most commonly cited
option used in research on living mulch. Sometimes efforts are even
made to collect the trimmed biomass and use it as an applied mulch
on the cash crop.
Partial rototilling entails the tillage of the
living mulch, while leaving one or more strips of the cover crop to
re-grow. This can be accomplished in a number of ways. Most tiller
designs naturally leave a narrow strip of untilled soil. If this is
inadequate, one or more sets of tiller tines can be removed. Partial
rototilling has been used most successfully in stoloniferous cover
crops like Dutch white and Ladino clover (7).
Resources
& Research on Living Mulches
One good example of research on insect management
with living mulches is provided later in this publication. For a good
overview, the article Fighting Insects with Living Mulches
in the October 1993 issue of The IPM Practitioner is recommended.
Somewhat dated, it still provides an excellent summary (29).
One of the best discussions of living-mulch
agriculture from an organic perspective was published in the October-December
2000 issue of HortTechnology (26).
After a good review of the literature, authors Leary and DeFrank describe
an idealized organic living mulch system that would have the following
features:
· a compatible, non-aggressive cover crop
· zone tillage to open and maintain a good seedbed
· concentration of composts, amendments, and organic fertilizers
in the tilled production strips
· mowing for living mulch suppression, with the clipped residue
collected and applied as an organic mulch to the crop
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Zone
Tillage
According to the strict definition, zone or
strip tillage is similar to no-tillage except that a narrow 5-7"
wide seedbed is established for planting. In no-till, a mere slot
is opened into the soil for planting. The narrow seedbed in zone tillage
is usually created by one or more gangs of fluted coulters mounted
on the front of the planter. In the broader sense used here for organic
farming, strip tillage will refer to any system in which a seedbed
strip is established through a cover crop or crop residue, while still
leaving a wide, untilled inter-row area.
Strip tillage offers certain advantages by encouraging
the earlier warming and drying of the immediate seedbed area. This
can be especially valuable in cold, wet spring weather. In traditional
no-till, where planting is done into a narrow slot, harvest can be
delayed by as much as 2-3 weeks in some areas. This can be a real
problem for growers trying to target a market window (30).
The loosening of the soil through zone tillage can also make for a
more desirable seedling environment. Farmer experiences, especially
with vegetable production, suggest that these are some very significant
advantages. Several organic vegetable growers in California, for example,
have reported that zone tillage made a great difference in the success
of their killed mulch systems (13).
Zone tillage appears to be one of the key technologies
that make killed mulch and living mulch systems work. In some instances,
the tilled zone may need to be fairly wide. It typically needs to
be managed with additional cultivation, hoeing, or traditional mulching
during the cropping season.
An early, farm-based living mulch system of
this sort was described in a 1991 New Farm article by Craig Cramer
(31).
The featured farmer was an organic produce grower in Minnesota, who
did much of his farming with draft horses and walk-behind equipment.
Winter squash was grown on fields planted to a winter cover crop of
oats and field peas the previous fall. When the soil warmed sufficiently
in spring, 2.5-3.5' strips were tilled on 6' centers and immediately
direct-seeded or transplanted to squash. For several weeks, weeds
in the cash crop strips were managed through horse-drawn cultivation
and hand-hoeing. When the remaining cover crop reached about 3 feet
of growth, it was mown using a walk-behind sickle mower. The residue
was then hand-raked into the squash-row as a mulch.
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Cover Crop
Technologies
There is no doubt that research and development
of cover crops has made—and will continue to make—a considerable difference
to the suitability and adaptability of conservation tillage to organic
systems. This is most obvious, of course, with killed or living mulch
systems—these approaches are defined by the specifics of how cover
crops are managed.
Though not a defined aspect of mulch or ridge
tillage, cover crops are also being given increased attention where
these systems are concerned. A particularly interesting article that
highlighted the need and potential for cover crops appeared in the
March-April issue of The New Farm. In Micromanaged Cover
Crops (32)
author Craig Cramer describes an Iowa ridge-till farmer's attempts
to simultaneously drill several different species of cover crops into
the varied micro-terrain of a ridge-tilled field. Oats, crimson clover,
and/or berseem clover were seeded on the ridge peaks; these species
winter-kill readily in Iowa and made early planting easier.
Mammoth red clover was seeded into the ridge
valleys to control erosion, and sweetclover into the wheel-track valleys
to break up compaction. These two species would be killed with the
first pass of the high-residue cultivator. Various difficulties were
encountered involving the differences in seeding rates required for
uniformly good stands, and with the capability of the cultivator to
fully kill well-established sweetclover. The story, however, illustrated
the kind of out-of-the-box thinking required to develop more sustainable
low-till technologies for organic cropping.
Good resources are now available to assist in
researching and selecting cover crops. The Sustainable Agriculture
Network's Managing Cover Crops Profitably is among these (33).
Also recommended are the Northeast Cover Crop Handbook (34)
and Covercrops for California Agriculture (35).
ATTRA also has a useful publication on this topic, titled Overview
of Cover Crops and Green Manures.
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Selected
Abstracts: No-Till/Low-Till Research and Writings Relevant to Organic
Systems
Living
Mulches for Vegetable Production
Researchers at the University of Illinois evaluated
four perennial "living mulch" covers—Dutch white clover,
red clover, perennial ryegrass, and canola—for the production of Hungarian
wax pepper and okra. The vegetables were established by transplanting
into tilled strips in the mulch treatments. A reasonable level of
in-row weed control was maintained by hand hoeing.
Crop yields were reduced by all the living mulch
treatments, but were lowest in the canola and perennial ryegrass treatments.
Mowing, as a means of living mulch suppression, improved crop yields
generally.
Biazzo, Jeromy and John B. Masiunas. 1998. Using
living mulches for weed control in Hungarian wax pepper (Capsicum
annum) and okra (Abelmoschus esculentus). Illinois Fruit
and Vegetable Crop Research Report. University of Illinois—Champaign.
January. p. 6.
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Spring-Sown
Cover Crops and Undercutting
The research on undercutting begun at Ohio State
early in the 1990s continues. Investigators spring-planted two winter
annuals, grain rye and field peas, both as monocultures and as bi-cultures
in varying proportions. The cover crops were undercut after two months
and tomato seedlings transplanted. Weed suppression was effective
for roughly six weeks. However, by that time, tomato growth was sufficiently
advanced to be unaffected by weed competition.
Yields were highest in plots that had 50% or
more of the cover in peas, apparently in response to greater nitrogen
availability. The soil loosening accomplished by undercutting also
appeared to have a positive effect on the transplants when contrasted
to control plots where this tool was not used.
Christine, Akemo Mary, Mark Bennett, and Emily
Regnier. 1998. Weed control in tomato production using spring-sown
cover crops killed by undercutting. HortScience. Vol. 33, No. 3. June.
p. 495.
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A
Living Mulch System for the South
In the mid-1990s, farmer researchers on a CSA
farm in Alabama began a research project with funding from the Organic
Farming Research Foundation. The objective of that research actually
related to composting. However, the information provided in their
research report describes a cropping system centered on annual use
of living mulches.
As a general practice, the entire growing area
on this farm is planted to Dutch white clover every fall. In the spring,
production beds are created by tilling to leave strips of clover as
walkways. The clover is managed during the growing season through
regular mowing. The trimmings are then composted and re-applied to
the beds. The viability of the living mulch walkways is dependent
on weather conditions. Hot and dry conditions strongly suppress the
growth of the clover.
Walz, Erica. 1998. Evaluating the use of living
clover mulch as a nitrogen source for compost. Organic Farming Research
Foundation Information Bulletin. No. 5. Summer. p. 10-11. Copies of
the full research report are available upon request from: Organic
Farming Research Foundation, P.O. Box 440, Santa Cruz, CA 95061 Tel:
831-426-6606, Fax: 831-426-6670 Email: <research@ofrf.org>.
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Snap
Beans in Killed Mulch Culture
The work done by USDA researchers Abdul-Baki
and Teasdale is among the most informative on the matter of killed
cover crops, highlighting both the potentials and the challenges of
this approach. Their efforts at growing transplanted broccoli and
tomatoes have already been discussed. For three years, they also evaluated
direct-seeded snap beans, again using a flail-mowed mulch of hairy
vetch.
Compared to conventional tillage plots, the
killed mulch plots produced higher yields with no additional nitrogen
fertilizer. Weed control was managed with a minimal amount of hand
weeding in two out of three years. In the third year, a flush of grassy
weeds in the no-till plot proved a problem. The researchers chose
to control it with an herbicide. The problem would have been more
significant under organic management where chemicals are not an option.
Abdul-Baki, Aref A. and John R. Teasdale. 1997.
Snap bean production in conventional tillage and in no-till hairy
vetch mulch. HortScience. Vol. 32, No. 7. December. p. 1191-1193.
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More
Research from Maryland: Cover Crop Mixtures vs. Monocultures
For three years, Abdul-Baki and Teasdale studied
the winter cover crops hairy vetch, grain rye and crimson clover,
as monocrops and in combination, as part of a mow-kill production
system for fresh tomatoes.
They observed, as expected, that combinations
of cover crop species generally produced greater biomass, and that
greater biomass provided better weed suppression. Also anticipated
was their observation that small-seeded annual weeds were the most
easily managed with this system, with a shift towards perennial weed
species likely over time. Also noted was the high carbon-to-nitrogen
ratio of the monocrop rye residue, suggesting the possibility of nitrogen
tie-up in the soil.
Of particular interest were the varying yield
results from year to year. In cool, wet years, mulched plots often
showed delays in crop maturity. Also of interest was the relative
performance of comparative plots where herbicides were used. As in
their other studies, Abdul-Baki and Teasdale used flail mowing to
kill the cover crops. They duly noted that this may not be the optimum
cover crop killing technology, due to the rapid decomposition of the
shredded biomass, which gives weeds a better chance at resurgence.
Teasdale, John R. and Aref A. Abdul-Baki. 1998.
Comparison of mixtures vs. monocultures of cover crops for fresh-market
tomato production with and without herbicide. HortScience. Vol. 33,
No. 7. p. 1163-1166.
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Vetch
Mulch Repels Colorado Potato Beetle
ARS entomologist Kevin Thorpe monitored the
Abdul-Baki/Teasdale trials for their effects on insect pests. He was
able to document that the hairy vetch mulch was decidedly repellent
to Colorado potato beetle—a pest of tomatoes in much of the country.
Anon. 2001. Vetch thwarts beetle. Small Farm
Today. January. p. 11. For more information, contact Kevin Thorpe,
ARS Insect Biocontrol Laboratory, 301-504-5139, <thorpe@asrr.arsusda.gov>.
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Living
Mulch as Beneficial Insect Habitat
Providing a beneficial insect habitat is one
of the possible benefits of living mulches. Researchers in Virginia
looked into the potential of various living mulches to assist pest
management in cucurbits (cucumbers and heirloom pumpkins). They made
a number of comparisons among buckwheat, oats/vetch, and oats/white
clover living mulches, with conventional and straw-mulched plots.
Living mulches clearly increased the numbers of key predator species
and demonstrated the potential of keeping the major pest—cucumber
beetle—below economic threshold levels.
Yields of living mulch plots lagged well behind
those of conventional practices. It was observed, however, that increasing
the crop-to-living mulch ratio could make a dramatic difference. When
a twin-row planting system was tried in the buckwheat plots, the crop:mulch
ratio was increased from 3:5 to 5:3. The yields from the twin-row
system increased 4.8 times over the single-row approach. However,
this greater yield was still only 72% of that achieved on the conventional
plots, indicating much more research is needed to develop systems
capable of "economically viable" yields.
Amirault, Jean-Pierre and John S. Caldwell.
1998. Living mulch strips as habitats for beneficial insects in the
production of cucurbits. HortScience. Vol. 33, No. 3. June. p. 524.
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Combining
Killed-Mulch and Living Mulch Technologies
In 1998 and 1999, the Virginia Tech researchers
continued their conservation tillage work with cucumbers. In this
instance, they planted and transplanted cucumbers into a rye/vetch
cover crop that had been killed by rolling. Inter-row strips of cover
crop were left untouched and allowed to flower as habitat for beneficial
insects. One hand-weeding was required at 3 weeks after planting to
obtain the same control achieved by herbicides. When compared to conventional
cucumber production using black plastic, the mulch plots had higher
numbers of predator insects, fewer cucumber beetles, lower incidence
of bacterial wilt, and yields 59% higher in '98 and 23% higher in
'99. The Virginia Tech folks appear much further along in finding
the "economically viable" systems they were seeking just
a few years earlier.
Caldwell, John and Maurice Ogutu. 2000. Effects
of rye-vetch no-till and habitat strips and black plastic mulch on
insect densities, weed control, and fresh-market cucumber growth and
yield. HortScience. Vol. 35, No. 3. June. p. 478-479.
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Allelopathic
Effects on Crops
It has been observed that allelopathy may not
only suppress weeds, but also damage certain crops, especially small-seeded
vegetable crops. Transplanting has occasionally been viewed as a means
of circumventing this problem.
Kentucky State researchers explored the possibility
of allelopathic damage to tomato, broccoli and lettuce crops transplanted
into a mow-killed sorghum-sudan mulch. All three crops suffered significant
allelopathic damage in the mulched plots. This killed mulch cover
is therefore not suitable for these crops.
Mitchell, J.P., et al. 2000. Potential allelopathy
of sorghum-sudan mulch. HortScience. Vol. 35, No. 3. June. p. 442.
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Bell
Peppers in Cowpea Mulch
A two-year conservation-till study was done
in Thermal, California to see if bell peppers could be successfully
grown using a mow-killed cowpea mulch. The bell peppers were transplanted
into the mulch and provided supplementary irrigation through a drip
system. Peppers in the cowpea mulch yielded 202% and 156% more in
dry weight, as compared to bare-ground culture, in '97 and '98 respectively;
resulting fruit size was comparable.
McGiffen, Milton E. and Chad Hutchinson. 2000.
Cowpea cover mulch controls weeds in transplanted bell peppers. HortScience.
Vol. 35, No. 3. June. p. 462.
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Tomatoes
in Killed Rye/Vetch in Massachusetts
As indicated earlier, it is a challenge to find
professional no-till/low-till research conducted in an organic context.
This piece of research is among the few exceptions. The investigators
(Mark Schonbeck, Peggy Elder, and Ralph DeGregorio) are well known
in sustainable and organic farming circles.
A series of experiments relating to cover crop
management were done on soils in Massachusetts that had a lengthy
history of biological farming management. The objective was to develop
information for gardeners and market gardeners. Among the trials was
one that tested a mow-killed mulch of hairy vetch and rye against
a more standard organic option in which the same cover crops were
tilled into the soil in advance of planting.
The results were quite positive. The tilled
plots produced more heavily early in the season, but the yield difference
shrank as the season progressed. In the end, the difference in total
yield between the mulched and tilled plots was not significant. The
time spent in later weed management on the killed-mulch plots was
about three-fourths that spent on the tilled plot. Mulched plots clearly
showed better moisture conservation.
The researchers alluded to potential problems
from pests—especially slugs—in mulch systems, though their trials
did not appear to be bothered. It is interesting to note that few
other investigators allude to problems with such pests; most appear
more focused on the pest control benefits mulches provide as beneficial
habitat.
Schonbeck, Mark, Peggy Elder, and Ralph DeGregorio.
1995. Winter annual cover crops for the home food garden. Journal
of Sustainable Agriculture. Vol. 6, No. 2-3.
p. 29-53.
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No-till
Pumpkins in NY State
In 2000, Cornell researchers investigated no-till
pumpkin production in a flail-mowed rye mulch. They looked at a number
of variables including the relative merits of transplanting vs. direct-seeding,
and short vs. long season varieties.
They found that the long-season variety ('Howden')
generally performed adequately under no-till, but did rather better
under conventional tillage. Transplanting was clearly better than
direct-seeding for 'Howden'. Apparently it responded well to the earlier
warming of soil under conventional tillage.
The situation was different for the short-season
variety 'Rocket'. 'Rocket' seemed to be especially well suited to
no-till and performed equally well whether transplanted or direct-seeded.
The investigators noted that future weed management research for these
systems needs to focus on suppression at 4-6 weeks after planting,
when weeds begin to push through the mulch.
Blomgren, Ted. 2001. Reduced-tillage pumpkins
studied in New York. The Vegetable Growers News. March. p. 15-16.
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Optimum
Timing for Rolling
Alabama researchers took a hard look at rolling
as a means for killing small-grain cover crops. The specific roller
under investigation was the roll-crimper—a large cylinder with strips
of angle iron welded lengthwise. This implement was of particular
interest because the manner in which it lodges the cover crops is
believed to be especially soil-protective. It also facilitates no-till
planting when the planter follows in the same direction taken by the
roller. Finally, rolling is inexpensive—about $1.50/acre, which is
the same as the cost of cultipacking.
Most of the experimental variations tested in
this trial involved the use of herbicides; investigators were seeking
to combine reduced-rate herbicide kill with the roller. The roller
was evaluated on its own, however, and this information is particularly
useful in an organic setting.
The cover crops tested in this trial were black
oats, rye, and winter wheat. The optimum stage for roll-killing any
of these cereals appeared to be after flowering and pollen shed, but
before soft-dough. The early milk stage seemed ideal. Black oats reaches
this stage earlier than either rye or wheat. This provides an advantage
for the grower needing to get into the field earlier to hit a market
window. Black oats, however, produces less biomass than either rye
or wheat so there is some loss of weed suppression.
Ashford, D.L. et al. 2000. Roller vs. herbicides:
an alternative kill method for cover crops. Proceedings of the
23rd Annual Southern Conservation Tillage Conference for Sustainable
Agriculture. June. pp. 6-7. <http://www.ag.auburn.edu/aux/nsdl/sctcsa/Proceedings/2000/2000_SCTCSA.pdf>.
Note that the highlights of Ashford's research
are featured in the May-June 2001 issue of Progressive Farmer,
in an article titled Cover Crops Too Tall? Roll 'Em Down. The
piece, by John Leidner, is of particular value due to the excellent
photos showing a home-built mower mounted on the front of a John Deere
4840 tractor, and a partially rolled stand of grain rye. To obtain
a back issue of Progressive Farmer, call 1-800-292-2340.
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No-till
Organic Broccoli
Virginia Tech's Ronald Morse included an organic
broccoli treatment as one part of a trial conducted to assess further
no-till potential. The organic system entailed transplanting broccoli
into a number of different monoculture and bi-culture cover crops
that were killed by flail-mowing. A side-dressing of blood meal was
used to supply supplemental nitrogen. The organic system was compared
to conventional clean tillage and conventional no-till systems in
which rolling was combined with herbicides, and ammonium nitrate was
used as a supplemental nitrogen source.
Soybeans, cowpeas, and foxtail millet were evaluated
as monoculture cover crops. Combinations of cowpeas/millet and soybeans/millet
were also tested. Dr. Morse observed that the soybeans/foxtail millet
was the most effective weed-suppressive mulch tried in the organic
plots. He noted that one hand-weeding or mechanical cultivation was
still required in these plots to keep weeds below "weed-limiting
threshold levels."
Dr. Morse also noted that nitrogen was a limiting
factor in the organic system. Though blood meal was applied at levels
to deliver the same amount of total N, yields were significantly lower
than in those plots receiving ammonium nitrate. Manures, additional
sidedressings, and/or foliar sprays were suggested as means for making
up the deficit.
It seems somewhat strange that nitrogen would
be deficient in the organic plots given the application of blood meal
at equivalent agronomic rates; it is among the most readily available
of organic supplements. Since it is likely that this research was
done on a field with a history of conventional management, it would
be interesting to learn if the same nitrogen deficit would be found
were the trial conducted on soil with years of organic care.
Morse, R. 2000. High-residue, no-till systems
for production of organic broccoli. Proceedings of the 23rd Annual
Southern Conservation Tillage Conference for Sustainable Agriculture.
June. pp. 48-51. <http://www.ag.auburn.edu/aux/nsdl/sctcsa/Proceedings/2000/2000_SCTCSA.pdf>.
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Desert
Production of Transplanted Lettuce
The desert valleys of Coachella and Imperial
in California produce a wide array of vegetables. The use of cover
crop mulches could not only suppress weeds but moderate soil temperatures
and possibly extend production windows. Trials in the Coachella Valley
evaluated cowpea residue as a mulch. Results were largely positive.
The residue mulch reduced weed control costs and allowed for earlier
planting due to moderated soil temperatures.
Ngouajio, Mathieu, et al. 2001. Reducing Weed
Population and Soil Temperature in Desert Vegetable Production with
Cowpea Mulch. Paper distributed at 2001 Eco-Farm Conference, Asilomar,
California. Author can be contacted at Department of Botany and Plant
Sciences, University of California, Riverside, CA 92521-0124.
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Farm
Production of No-Till Garlic
Pennsylvania farmers Eric and Anne Nordell have
earned a reputation as highly innovative organic market gardeners,
making a modest living on limited acreage. Articles by them are a
frequent feature in Acres USA, the Small Farmer's Journal,
and other alternative agriculture publications. An article in the
May 2001 edition of Maine Organic Farmer & Gardener details
their no-till system for growing garlic, which is still under development:
They (the Nordells) adapted a subsoiler
so that it makes slits in a cover crop of oats and peas. They plant
garlic by hand into the slit, and the oats and peas die back over
the winter. In the spring, their no-till garlic came two weeks earlier
than garlic that had been heavily mulched and grown in the traditional
manner.
The Nordells utilize a number of techniques
involving planned rotations, interseeding, beneficial insect refuges,
summer fallowing, and cover cropping. Their farm is a fascinating
study in low-input sustainable farming. They have produced a video
that presents an overview of their farming system, plus a collection
of articles they've written. The video and the information packet
are available for $10 each (p&h included) from: Anne & Eric
Nordell, RD 1, Box 205, Trout Run, PA 17771.
English, Jean. 2001. Rotating out of weeds.
Maine Organic Farmer & Gardener. March-May. p. 18-19.
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An
On-Farm Living Mulch System in Montana
Helen Atthowe, a part-time horticulture agent
in Missoula County, Montana, farms about 3 acres of intensive organic
vegetable crops. Among the production systems she is using and refining
are living mulches, consisting mostly of clovers and medics. With
financial support from a SARE grant, Helen has documented nutrient
changes over time in the living mulches and the production beds.
For the details of Atthowe's study contact Western
Region SARE, Rm. 322, Agriculture Science Bldg., 4865 University Blvd.,
Utah State University, Utah 84322. Helen Atthowe can be contacted
directly at Biodesign Farm, 1541 South Burnt Fork Rd., Stevensville,
MT 59870, email <mslss@mssl.uswest.net>.
Weiss, Christine Louise. 1999. Biodesigning
your farm. Acres USA. May. p. 21-23.
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California
Research Underway
In late 2000, UC Santa Cruz's Center for Agroecology
& Sustainable Food Systems announced that they had begun experimentation
with organic conservation tillage. The first trials will evaluate
several cover crop combinations and management methods to assess their
suitability for organic pumpkin production. The principal investigators
involved in this effort are Jim Leap and Jeff Mitchell. Results of
the Center's work will be published in their newsletter The Cultivar.
Brown, Martha. 2000. Center takes part in conservation
tillage study. The Cultivar. Vol. 18, No. 2. Fall-Winter. p. 5. Subscriptions
to and back issues of The Cultivar are available from: CASFS,
University of California, 1156 High St., Santa Cruz, CA 95064 Tel:
831-459-4140, Fax: 831-459-2799, Website <http://zzyx.ucsc.edu/casfs>.
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A
Guide to Zone Tillage
For many years, the late Don Schriefer was one
of a "stable" of speakers and authors on sustainable farming
promoted by the popular publication Acres USA. His insights
into soils, tillage, and fertilization were practical and highly respected.
The posthumous publication of his book Agriculture
In Transition is most welcome. Several pages are spent contrasting
the effects of different tillage systems on soils and crops. He speaks
most strongly about zone tillage and why it works so well for a growing
number of farmers.
Agriculture In Transition is available
in softcover (238 p.) for $27 (p&h included) from Acres USA, P.O.
Box 91299, Austin, TX 78709, Tel: 800-355-5313, Fax: 512-892-4448.
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Summary
The rapid growth in organic agriculture has
helped to spur research in herbicide-free conservation tillage. Interest,
however, is not confined to the organic sector. A recent article in
No-Till Farmer (36)
spotlighted a fledgling Canadian group called the Pesticide Free
Farmers Association. The formation of this group was motivated
by a now familiar set of factors—the growing costs of chemical-intensive
farming, opportunities in 'green' marketing, and concerns about sustainability.
While not organic, this group of farmers is intent on developing successful
no-till production systems that work without pesticides. These growers
have the relatively modest objective of not using pesticides for one
or more years within a rotation and marketing their production in
those seasons under a "green" label. Pesticides—particularly
herbicides—will be allowed in "off years" to keep control
of weed populations.
Compared to these Canadian growers, organic
farmers face greater constraints and challenges because synthetic
herbicides can never be an option. This IS an important point. Unless
cultivation is already comfortably integrated into the system—as it
is with mulch and ridge tillage—there must be a fall-back option for
weed control. The fall back options will certainly be needed at two
points. The first of these involves controlling biennial and perennial
species that escape and predominate under no-till/low-till culture.
Organic growers can still use traditional tillage options in such
cases. Certain crops in rotation can be grown with traditional organic
cultivation so that low-till/no-till culture can be employed for some,
if not most, of the years within a cycle. For the near future at least,
this appears to be a reasonable strategy for most farmers.
Similarly, some forms of hoeing or cultivation
will likely be needed within most low-till systems. Where zone tillage
and living mulches are used, some mechanical weed control will likely
be needed for much of the season. With killed mulches, it will be
needed mostly in the late season.
Some of the new classes of herbicides may also
play a role in expanding organic conservation tillage options. Contact
herbicides with active ingredients such as fatty acids, vinegar, lemon
juice, and clove oil might be allowed for organic production in the
future. They might be used as a means of killing or suppressing cover
crops and/or as in-season weed control tools if protective shielding
is used to protect the crop. Some forms of thermal weeding may also
be useful. However, flaming could be a fire hazard if used where significant
amounts of dried residue are accumulated.
There are additional dimensions to conservation
tillage that this publication barely addresses. Among the most glaring
is the relationship between conservation tillage and insect pest and
disease incidence. While a few abstracts—primarily dealing with insects—are
provided in the text, the available research on these developing systems
is still quite limited. While there is a natural tendency to extrapolate
from the experiences under conventional conservation tillage, insect
pest and disease pressure under organic management may be considerably
different. Predictions and conclusions should be drawn with caution.
While organic conservation tillage systems are
certainly worthy of pursuit, it is clear that there is much to be
learned before the more radical of these—killed mulches, living mulches,
etc.—can be widely adapted. Most, if not all, strategies will require
some cultivation
at least for the near term. As imperfect as
such systems might be, they will still contribute greatly to the sustainability
of organic agriculture and should be pursued vigorously.
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References
- Plowman's Folly is now available as
Plowman's Folly and A Second Look (Conservation Classics)
for $38 from <http://www.amazon.com>.
- Robertson, G. Philip, Eldor A. Paul, and Richard
R. Harwood. 2000. Greenhouse gases in intensive agriculture: contributions
of individual gases to the radiative forcing of the atmosphere. Science.
Vol. 289. September 15. p. 1922-1925.
- Lockeretz, Wm., Georgia Shearer, & Daniel
Kohl. 1981. Organic farming in the Corn Belt. Science. Vol. 211, No.
6. February. p. 540-547.
- The Alternatives in Agriculture Reports
are updated annually. The 2001 report is available for $10 postage
paid from: Thompson On-Farm Research, 2035-190th St., Boone, IA 50036-7423.
Tel: 515-432-1560.
- Conservation Technology Information Center,
1220 Potter Drive, Rm. 170, Purdue Research Park, West Lafayette,
IN 47906-1383 Tel: 765-494-9555, <http://www.ctic.purdue.edu>.
- Conservation Tillage Systems and Management:
Crop Residue Management with No-till, Ridge-till, Mulch-till, and
Strip-till, Publication #MWPS-45, is available for $30.50 ($25
plus $5.50 p&h) from NRAES, Cooperative Extension, 152 Riley-Robb
Hall, Ithaca, NY 14853-5701, Tel: 607-255-7645, Fax: 607-254-8770,
Email: <nraes@cornell.edu>.
- Creamer, Nancy G. and Seth M. Dabney. 2002.
Killing cover crops mechanically: Review of recent
literature and assessment of results. American
Journal of Alternative Agriculture. Vol. 17, No. 1. Pp. 32-40.
- Creamer, N., et al. 1995. A method for mechanically
killing cover crops to optimize weed suppression. American
Journal of Alternative Agriculture. Vol. 10, No. 4. Pp. 157-162.
- Creamer, N. 1999. An evaluation of summer cover
crops as weed suppressive mulches in vegetables. Organic Farming Research
Foundation Information Bulletin. Summer. 14-16.
- Mitchell, Jeff. 2001. Presentation given as
part of a workshop titled: "The Best of Both Worlds: Organic
Low- and No-till Research," at the 21st Annual Ecological Farming
Conference, January 24-27, Asilomar, CA. An audio tape of this workshop
(order #D080) is available for $8.50, s&h included, from: Audio
Productions, Inc., P.O. Box 1259, Lake Stevens, WA 98258, Tel: 800-488-5455,
Fax: 425-334-7866, Email <aptapes@aol.com>.
- Editors. 1994. Smart tillage tools. The New
Farm. Vol 16, No. 5. July-August. p. 31-40.
- Morse, Ronald. 1998. Keys to successful production
of transplanted crops in high-residue, no-till farming systems. Proceedings
of the 21st Annual Southern Conservation Tillage Conference for Sustainable
Agriculture. July.
<http://www.uark.edu/depts/agripub/Publications/specialreports/>.
- Klauer, Helmut and Scott Parks. 2001. Separate
presentations given as part of a workshop titled: "The Best of
Both Worlds: Organic Low- and No-till Research," at the 21st
Annual Ecological Farming Conference, January 24-27, Asilomar, CA.
To order an audio tape of this workshop, see reference #9.
- Pester, Todd. 1998. Allelopathic effects of
rye (Secale cereale L.) and their implications for weed management—a
review. Colorado State University, Fort Collins, CO. <http://www.colostate.edu/Depts/Entomology/courses/en570/papers_1998/pester.htm>.
- Boydston, Rick A., and Amm Hang. 1995. Rapeseed
(Brassica napus) green manure crop suppresses weeds in potato
(Solanum tuberosum). Weed Technology. Vol. 9. p. 669-675.
- Stivers, Lee, Frances Tucker and Claudia Olivier.
1998. Brassica cover crops for vegetable production. Maine Organic
Farmer & Gardener. March-May. p. 33.
- Madden, Nick. 2001. Presentation given as part
of a workshop titled: "The Best of Both Worlds: Organic Low-
and No-till Research," at the 21st Annual Ecological Farming
Conference, January 24-27, Asilomar, CA. To order an audio tape of
this workshop, see reference #9.
- Abdul-Baki, Aref A. and John R. Teasdale. 1997.
Sustainable Production of Fresh-Market Tomatoes and Other Summer Vegetables
With Organic Mulches. Farmers' Bulletin 2279. USDA-ARS, Beltsville,
MD. 23 p. Copies of this publication can be obtained from: Dr. Abdul-Baki,
Rm. 213, Bldg. 10A, Beltsville Agricultural Research Center, Beltsville,
MD 20705.
- Abdul-Baki, Aref A., et al. 1997. Broccoli
production in forage soybean and foxtail millet cover crop mulches.
HortScience. Vol. 32, No. 5. August. p. 836-839.
- Heacox, Lisa. 1998. Broccoli into beans. American
Vegetable Grower. February. p. 24, 26-27.
- Cramer, Craig. 1993. Micromanaged cover crops.
The New Farm. Vol. 15, No. 3. March-April. p. 29-30.
- McDermott, Maura. 2000. Grant tests cover crops.
Field Notes. (Published by The Kerr Center for Sustainable Agriculture,
Poteau, OK.) Winter. p. 4-5.
- The Kerr Center for Sustainable Agriculture,
P.O. Box 588, Poteau, OK 74953, Tel: 918-647-9123, Email <aeware@kerrcenter.com>.
- Hofstetter, Bob. 1993. Smother crops: plant
a grain in the "wrong" season for the right cover. The New
Farm. May-June. p. 39-41.
- Costello, Michael J. and Miguel A. Altieri.
1994. Living mulches suppress aphids in broccoli. California Agriculture.
Vol. 48, No. 4. July-August. p. 24-28.
- Leary, James, and Joe DeFrank. 2000. Living
mulches for organic farming systems. Vol. 10, No. 4. October-December.
p. 692-698. HortTechnology is published by the American Society for
Horticultural Science (ASHS). A non-member subscription is $40. Back
issues are available for $14 each, s&h included. Contact: ASHS
Business Office, 113 South West Street, Suite 200, Alexandria, VA
22314, Tel: 703-836-4606, Fax: 703-836-2024, Email <pubs@ashs.org>.
- Paine, L.K. and H. Harrison. 1993. The historical
roots of living mulch and related practices. HortTechnology. Vol.
3, No. 2. April-June. p. 137-143.
- Ilnicki, Richard D. and Adrian J. Enache. 1992.
Subterranean clover living mulch: an alternative method of weed control.
Agriculture, Ecosystems and Environment. Vol. 40. p. 249-264.
- Grossman, Joel. 1993. Fighting insects with
living mulches. The IPM Practitioner. Vol. 15, No. 10. October. p.
1-8. The IPM Practitioner is a benefit of membership in the Bio-Integral
Resource Center (BIRC). Annual memberships for an individual cost
$35. Specific reprints are available for $7.50, which includes s&h.
Contact: BIRC, P.O. Box 7414, Berkeley, CA 94707, Tel: 510-524-2567,
Fax: 510-524-1758, Email <birc@igc.org>,
Website <http://www.BIRC.org/>.
- Phatak, Sharad C. and Rick Reed. 1999. Opportunities
for conservation tillage in vegetable production. Proceedings of the
22nd Annual Southern Conservation Tillage Conference for Sustainable
Agriculture. July.
<http://www.nespal.org/sctc/Master.Proceedings.pdf>.
- Cramer, Craig. 1991. Cover crops replace plastic.
The New Farm. July-August. p. 30-31.
- Information on Steve Groff's experience with
no-till can be found in a number of places. Of particular note is
a cover article, Making No-Till Work, by Christine Weiss, in the February
1999 issue of Acres USA. Back issues of Acres USA are
available for $5 from Acres USA, P.O. Box 91299, Austin, TX 78709-1299,
Tel: 512-892-4400. Information can also be found at Groff's website
<http://www.cedarmeadowfarm.com/>
and through a video highlighting his no-till practices. The video
is especially instructive as it shows Groff's Buffalo rolling
stalk chopper in action. The video is available for $24.95 (s&h
included) from Steve Groff, Cedar Meadow Farm, 679 Hilldale Rd., Holtwood,
PA 17532
Tel: 717- 284-5152, Email <sgroff@epix.net>.
- Sustainable Agriculture Network. 2000. Managing
Cover Crops Profitably, 2nd edition. Sustainable Agriculture Network,
Beltsville, MD. 212 p. This book is available for $19 and the CD for
$10. The book and CD can be purchased as a set for $24. Please add
$3.95 s&h for the first item and $0.95 for any items thereafter.
Order from: Sustainable Agriculture Publications, Room 210 Hills Bldg.,
University of Vermont, Burlington, VT 05405-0082, Tel: 802-656-0584,
Fax: 802-656-4656, Email <sanpubs@uvm.edu>.
- Sarrantonio, Marianne. 1994. Northeast Cover
Crop Handbook. Rodale Institute, Emmaus, PA. 118 p. Available for
$12.95 plus $5.50 s&h from: Rodale Institute Bookstore, 611 Siegfriedale
Road, Kutztown, PA 19530, Tel: 610-683-6009, Email <info@rodaleinst.org>,
Website <http://www.rodaleinstitute.org>.
- Miller, P.R., et al. 1989. Covercrops for California
Agriculture. California Extension Leaflet No. 21471. University of
California, Davis, CA. 24 p. Available for $3.50 plus $1.50 s&h
from: University of California, ANR Publications, 6701 San Pablo Ave.,
Oakland, CA 94608-1239, Tel: 510-642-2431, Website <http://anrcatalog.ucdavis.edu>.
- Rance, Laura. 2001. Can you no-till and still
work toward being pesticide-free? No-Till Farmer. April. p. 12-13.
Annual subscriptions to No-Till Farmer cost $37.95; back issues
are $4 each. Contact: Lessiter Publications, P.O. Box 624, Brookfield,
WI 53008-0624, Tel: 800-645-8455, Fax: 262-782-1252, E-mail <info@lesspub.com>,
Website <http://www.lesspub.com/>.
Return
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Further
ATTRA Resources
The following ATTRA publications are directly
related to the subjects discussed in this document:
Overview of Cover
Crops and Green Manures
Conservation Tillage
Overview of Organic Crop Production
Principles of Sustainable Weed Management
Farmscaping to Enhance Biological Control
ATTRA program specialists Steve Diver and Preston
Sullivan have made diligent efforts to follow developments in conservation
tillage for vegetable and agronomic crops respectively. Both have
additional information and materials to share on these topics.
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Acknowledgements
Special thanks for assistance in this document
go to Dr. Nancy Creamer at North Carolina State University, for permission
to use an early draft of her article; to Dr. Mary Gold at the Alternative
Farming Information Center at the National Agriculture Library, for
research assistance; to Steve Diver, ATTRA program specialist, for
guidance to hard-to-find resources. Reviews were provided by ATTRA
specialists Barbara Bellows, Katherine Adam, Nancy Matheson, Holly
Born, Ann Wells, and Richard Earles.
Return
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By George
Kuepper
NCAT/ATTRA Program Specialist
June 2001
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