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Posted April 12, 2007: What the world needs
now is cover crops (and love, yes). There is too much bare,
eroded, over-exploited ground, and not enough stuff anchoring
it and revitalizing it.
This is something not only farmers should care about (and
I know that apathy is not difficult, because before I came
to work as an intern at The Rodale Institute, the concept
was meaningless to me as a non-farmer). There are cover crops
for every soil type, climate and nutrient-deficient terrain.
There are cover crops to satisfy even the most demanding and
high-maintenance vegetable or field crops. There are some
that are prepared to survive even the cruelest conditions,
reclaim marginal land and begin to remedy today’s most
pressing environmental concerns, from global warming to the
depletion of finite resources like topsoil, soil nutrients
and water (problems that non-farmers in the industrialized
world are rarely confronted with).
Individuals who work directly with these resources have to
face the effects of their scarcity. Sadly, as mere individuals,
they are often ill-equipped and ill-informed to reach a solution.
The genetic resources of cover crops have vast and often
untapped potential. Our agricultural industry seems bent on
whittling down the crop gene pool to select for only the highest-yielding
varieties that can be cropped intensively and homogenously,
disregarding other attributes, and then solving the problems
it has created through the artificial variation of genetically
engineered crops and chemicals to match. We had everything
we needed at our fingertips in the now-dwindling natural gene
pool, and that genetic material was actually integral to its
environment (with safe and predictable “side effects”).
One grim manifestation of this genetic consolidation and
loss of biodiversity is that at least one-quarter of the food
products sold today contain several ingredients derived from
a single crop—corn. As Michael Pollan observes in his
recent bestseller The
Omnivore’s Dilemma (Penguin, 2006), “The food
industry has done a good job of persuading us that the forty-five
thousand different items or SKUs in the supermarket—
seventeen thousand new ones every year—represent genuine
variety rather than so many clever rearrangements of molecules
extracted from the same plant.”
Cultivar trials present us with an array of valuable traits
that can be endlessly combined and recombined in polycultures
or selection processes. Adaptability and versatility of the
cover crop can be as important or more important than that
of the main crop, since it is setting the stage by building
up nutrients, soil structure and permeability (important for
the more efficient use of water and nutrients).
After the rollercoaster ride of a winter we had this past
year, the resilience of many of our overwintering crops was
striking, as was the greatly varying levels of resilience
among different cultivars of the same crop. Winter annual,
biennial and perennial plants never cease to amaze me in their
capacity to endure extremely harsh conditions. Even a brown,
lifeless, crunchy mess can often belie a rich life-support
system (concealed underground or in small nubs pushing from
the base of the stem) of stored carbohydrates, ready to send
up tender green shoots at the first blush of warm weather.
Many of our hairy vetch accessions that appeared to be winter-killed
had, upon closer examination, new shoots with baby leaves
beginning to unfold. Others simply had a deceptive brown top
layer that sheltered surviving life just below. Our cover
of ladino clover (a perennial clover) is at first glance just
a dense brown mat of residue. Peel back this layer, however,
and you find thick, green stems pushing out rows of unfolding
leaves. The biennial clovers—tall, dead stalks—showed
the first signs of regeneration with barely perceptible green
buds next to the base.
A robust and extensive root system is the plant’s
true engine for survival and growth. Too much aboveground
biomass before temperatures drop below freezing can actually
be a liability, especially in leguminous crops with vulnerable
nitrogen-rich tissue. The root and crown (the interface between
root and stem) have thick, hardy tissue with high carbon content,
storing sugars and carbohydrates throughout periods of cold
weather. Our greenhouse trials of hairy vetch from different
seed tag origins illustrated that the hardier hairy vetch
from Nebraska or Minnesota did not at first produce the most
rapid growth, but tended to put out multiple stems more quickly,
evidence that crowns had formed. Crowns are crucial because
they will be responsible for generating the plant’s
second-year growth after overwintering.
Hairy vetch turned out to have a high threshold for pain,
and therefore is one of the most widely adaptable cover crops
across many different climates. Our evaluation revealed that
the majority of kill took place after temperatures dipped
below 15°F and remained around 5°F-7°F for a period
of time. If there had been snow cover during this time, the
vetch probably would have survived. Even the insulation provided
by a nurse crop of oats was sometimes enough shelter for the
vetch, since the dense bent-over residue formed a tent under
which we found perfectly green vetch in late March.
Winter-hardiness is just one genetic dimension to consider
for cover crops in a rotation. Sweetclovers are another highly
adaptable cover crop that can tolerate a wide range of conditions
and whose uses range from green manure to forage to bee pasture
to mine reclamation solution. Our 2006 crop of annual sweetclover
(also known as Hubam clover) was a prolific nectar producer
and was a constant hum of insect life. Each of its racemes
may contain as many as 100 flowers, with up to 1,500 flowers
on a single plant. They most commonly draw honeybees, tachinid
flies and large predatory wasps, which will keep harmful pests
in check for the following crop and can help to break up existing
pest life cycles. Irregularity of flowering times ensures
an inflorescent season of several months.
Sweetclovers can grow in almost any ground that is not acidic—infertile,
eroded soils, poorly drained soil, overly-drained soil, soil
with too much organic matter such as peat, or clay soil with
hardly any organic matter. It tolerates environments from
sea level up to 4,000 feet in altitude. Its one major requirement
is calcium. It improves any soil it grows in with its penetrating
root structure that reaches several meters deep, breaking
up compacted soil, improving drainage and soil tilth, and
bringing leached nutrients from the subsoil up into more easily
accessible regions of the soil profile. This makes it extremely
valuable not only in a rotation or as a forage, but in restoring
marginal or depleted land. It self-maintains with the vigor
of a weed in these demanding conditions, reseeding itself
every other year (or every year if it is an annual variety).
Its high proportion of hard seed (about 50 percent), frustrating
to seed producers and farmers, becomes a major survival asset,
staggering the onset of germination and even delaying it for
up to 20 years.
As a warm-season crop, sweetclover was widely used in the
South before the advent of chemical fertilizers in the 1950s,
especially in Texas. It grows more quickly in hot weather
than any other crop, exceeding even alfalfa in its summer
biomass production, and has no problem with drought. Annual
sweetclovers are especially suited to hot weather. Prior to
World War II, 500,000 to 600,000 acres were planted with sweetclover
annually in Texas, and research from half a century ago on
improving its forage quality and its use as ground cover is
now being rediscovered at Texas agricultural experiment stations,
especially as the price of oil—and synthetic nitrogen—skyrockets.
Legume cover crops, and cover crops in general, have fallen
out of favor since World War II. When chemicals are readily
available, and are quick and easy, who cares about planting
an extra crop? The benefits to soil, the environment and even
yield are not immediately apparent, and we want an input that
“pays off” right away, a quick return on investment.
Too often, techniques we have come to call “organic
practices” are isolated, maintaining a distinct set
of associations. We only turn to them when in sustainability
mode; otherwise, they can stay up on their shelf. It is still
a relatively niche market for a particular niche pattern of
thinking, and we fail to see the big picture or the possible
unexpected applications of organic cultural practices.
Environmentalists and farmers worry about preserving soil
and defending the land against erosion, but they seldom choose
cover crops as an immediate solution. Instead, overworked
land is simply prescribed a “rest period” and
taken out of production and commission. No-till methods are
often claimed as the farmer’s panacea—just don’t
break up the soil, and preserve its integrity, they are told.
This is certainly a huge step in the right direction, but
conventional no-till methods are typically used in monoculture
or very short corn-soybean rotations and are still heavily
dependent on herbicide applications for weed control, insecticides
for control of such common pests as corn root worm, and synthetic
nitrogen for fertility.
Cover crops add the crucial element of biodiversity, mixing
in different combinations of rhizospheres (the plant’s
root-zone environment and the most active microbial site in
the soil) to the rotation, different nutrients and different
pest cycles. No-till is indeed a positive step, but it too
often fails to go far enough and ends up preserving the status
quo of continuous corn or two-crop rotations with no true
rejuvenation of the soil.
Planting cover crops is the proactive step to take, instead
of falling into complacency or helplessness, believing the
only way to protect endangered topsoil is simply to stop using
it, or to disturb it a little less. Cover crops do have the
potential to enhance tillage, no-tillage and minimum-tillage
systems. They sequester carbon from the atmosphere and store
it in the soil in the form of organic matter. They scavenge
leached nutrients and enable the soil to better retain them
in an available form, and they impede the lateral flow of
water across the soil surface. They can survive unimaginable
conditions and regenerate the ground into a habitable and
fertile place for other species. There is a cover crop to
fit almost any situation, and we can still reclaim this valuable
gene pool and tap into its potential to rebuild eroded rangelands,
grasslands, cultivated land and many other seemingly dead
or abandoned corners of the earth.
On a personal note: The Rodale Institute is one of the few
research stations in this country where it is possible to
test crucial and groundbreaking organic practices on a long-term
basis. Even the most basic organic management techniques are
relatively dead to the mainstream agricultural consciousness,
as the ag-chemical industry gains a deeper toehold in our
institutions of higher learning, warping and corrupting our
most trusted sources of knowledge and innovation. I feel extremely
privileged to have had the opportunity to work as an intern
at The Rodale Institute and to learn from its passionate researchers
and staff. They are independent thinkers willing to run against
the grain, and to put to the test what conventional agronomists
say can’t be done. I want to thank them for their inspirational
leadership, and for the support and vision of Ardath Rodale,
without whom none of the Institute’s work would be possible.
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