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  • From: "Tradingpost" <tradingpost@lobo.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] Dr. Ray Weil - Let's talk about soil
  • Date: Tue, 15 Jul 2008 20:18:03 -0600


from Rodale Institute
http://www.newfarm.org/columns/ray_weil/2003/0103.shtml
Let's talk about soil
We want soil to work for us, says soil scientist Ray Weil. We want it to hold
water, recycle nutrients and keep diseases at bay. But we pulverize it with
plows and expose it to evaporation and erosion. Now, does that make sense?

By Pat Michalak

January, 2003: Dr. Ray Weil (pronounced “Let’s talk about soil quality for a
WHILE”) is a professor of soil fertility and ecology at the University of
Maryland, and an internationally recognized leader in research on soil
quality and in soil science education. Attend one of Weil’s lectures, and
you’ll wonder, “How valuable is my soil? What am I doing to improve it?”

Land has a known economic value, but ponder for a minute the value that you
add to your soil. Has its condition improved or deteriorated? Are you killing
your soil? Unfortunately, soil quality is difficult to measure.

We want soil to work for us. It has to absorb and hold water; it must
breathe; soil should recycle nutrients; and, it should help to keep diseases
at bay. Below, Dr. Weil tells farmers, especially those in the Northeastern
United States, how to put their soil to work and build soil quality at the
same time.

“A farmer thinks, ‘I’ve only got 10 acres or 20 acres and I’m growing
strawberries and other high value crops like sweet corn. How can I take some
of my land out of production and plant wheat or cover crops that aren’t worth
much?’”

Take a small part of your farm out of production, says Weil. Find a little
slice of land that you can start to improve, then add more slices each year.
That way, some of your land is on the road to recovery. When you finally get
a high value crop on it, you’ll notice that your soil is much more
productive. Over time, proper soil management helps to improve soil quality.
Follow these guidelines when managing your slice:

* Reduce or eliminate tillage. In a five-year rotation, include at least
three years without tillage.
* Smooth the tillage transition by including cover crops and legumes in
your rotation, and leave plenty of residues.
* Select crop varieties that produce plenty of growth above- and
belowground. As with building muscle, you won’t wear soil out by growing big
plants on it. You’ll improve it!
* Apply animal manure, and other organic materials. But if the organic
material is not homegrown, be sure to avoid applying excessive nitrogen or
phosphorus in the process.
* Use lime, if needed, to adjust soil pH and raise calcium levels.
* Limit or eliminate herbicides and pesticides in order to encourage
natural cycles of pest control.

“Tillage is usually a few steps forward and a few steps back. Natural
processes, and not tillage, will make your soil loose.”

Stop stirring up your soil. Don’t break up the soil aggregates. Tillage
stimulates both erosion, and the loss of organic matter. If you feel you must
till, be sure to use an implement that makes cracks in the soils, but doesn't
turn it over. Better yet, try a system that doesn't use tillage at all. Once
you stop tilling, it may take several years for natural processes to take
affect. It’s usually around the third or fourth year that you’ll see things
turn around. Organic no-till is a greater challenge, and may require several
more years. The worst thing you can do is keep a soil bare by tilling several
times each year. Surprisingly, most crops can be grown under no-tillage—very
small seeded crops like lettuce may be exceptions.

“Put roots first. Roots are the way to go. You want to plant cover crops with
a lot of roots, and then leave the roots underground.”

Cover crops and organic matter at work: Root channels and worm channels
facilitate plant growth.

When is it easiest to push through a soil? Answer: When it’s wet in early
spring. That’s when cover crops are growing —those are the plants that break
through soil compaction. Cereal rye has a good root system that is active in
the early spring. Cover crops with taproots are good, too. Try to add oilseed
radish, dandelions or mustards to your crop rotation in order to increase
root biomass.

“In the forest, 90% of this years roots are growing down channels where roots
have already been. It’s just like hiking in a thicket—it requires too much
energy to bushwhack, so you follow a deer trail.”

At Steve Groff’s farm in Pennsylvania (see farmer profile at left), Dr. Weil
found a plow pan between 6-20” deep. However, Groff had stopped tilling his
soil, and mulch formed on the soil surface. The mulch attracted earthworms
that created channels deep within the soil. The channels allow for drainage,
while the organic-rich channels walls are known to be good at absorbing
pesticides and nutrients that might otherwise wash from the soil. Steve’s
vegetable roots grew right down the earthworm channels, right through the
compaction zone. With earthworms working for you, you don’t need a subsoiler.
By leaving the soil untilled, root channels remain open and new roots will
follow the same channels. Earthworm numbers will increase in most parts of
the USA.

“Think of an acre of land and picture a full-size pickup truck overloaded
with this huge pile of fungal hyphae and bacterial slime. A good heaping
pickup load would be 1 – 1 ½ tons. That’s the living biomass you’re aiming
for.”

Although you won't see them on most soil test reports, there’s more than just
one kind of organic matter. Organic matter is actually a diverse bunch of
compounds, many which haven’t been identified. Active organic matter (less
than 1/5 of total organic matter) contains a myriad of living organisms and
materials they use as food. When these organism "eat" the organic matter (and
each other) they release plant nutrients such as N, S and P as well as
micronutrients.

When you clear land in native vegetation and start plowing it, within a few
years you’ll lose most of the active organic matter and that’s when the soil
quality goes down. Fortunately, you can increase the active fraction since
that’s the part that accumulates first. When farmers have a problem field
that just doesn’t yield as well, low active organic matter is often the
culprit.

Passive organic matter is protected from microorganisms because it is
chemically too hard to "digest' or because it is tucked away inside soil
aggregates where even tiny bacteria cannot get at it. Much of the passive
organic matter in soil has been there for centuries, even millennia. It turns
over very, very slowly, so it does little to release nutrients or increase
microbial activity.

However, passive organic matter acts much like a sponge, holding a lot of
water. It provides much of the soil's cation exchange capacity that makes
calcium, magnesium, potassium and other nutrients available to plants and
prevents them from washing away. It’s a kind of long-term storage or
“capital” of nutrients decades and centuries.

Passive organic matter also plays a role in global climate change. Most
agricultural soils have about one-half the carbon as they had under natural
vegetation. That’s mainly because tillage speeds the decomposition of organic
matter. During this process microorganisms turn the carbon in organic matter
back into carbon dioxide gas that adds to the amount of this greenhouse gas
in the atmosphere.

If we can build up passive organic matter in soils, we can undo some of the
past losses. Crops take carbon dioxide out of the atmosphere and turn it into
compounds like sugars and cellulose. Eventually some of this carbon is
returned to the soil in plant residues, and transformed into soil organic
matter, thus lowering the amount of this gas that can contribute to global
warming.

When you’re trying to improve your soil, it takes much longer to increase the
passive organic matter than the active. However, the passive organic matter
sequesters the carbon in the soil for a much longer time than the active, and
therefore it is most important in combating global warming.

“If your soil clods can't pass the water test, change your management
practices. It will help your bottom line as well as the soil.”

Simple clod test: Healthy soil, at left, holds together in water, while poor
soil falls apart.

You can perform a simple soil aggregate stability test at home with a soil
sample, a small glass jar and some tap water. Several days before, collect
the soil. Include soil from a “problem” field, as well as soil from a fence
row or field you feel is in excellent condition, such as one coming out of
sod. Allow the samples to
dry at room temperature. Fill two glass jars half way with water, then place
a dry clod of soil from each sample into its jar. Stir the water gently.
Watch closely to see whether the clod remains intact or falls apart (as in
the photo).

Soil that falls apart and gives off few air bubbles has poor aggregate
stability. Soil clods that hold together, that absorb water easily, and that
emit air bubbles indicates soil with good aggregate stability and a good
portion of active organic matter. According to Dr. Weil, “Good soil should be
at least 50% air space (that’s where the bubbles come from). If your soil
clods hold together, and the water stays clear, even when you stir, you’re
probably on the right track with soil management. Keep doing what you’re
doing.” Farm fields managed without tillage have the greatest aggregate
stability, because as the active organic matter increases, microorganism
numbers increase. Microorganisms are the critters that produce the glues that
hold the soil together. You can improve soil quality and aggregate stability
by adding amendments like manure, but if you follow with a plow, you may do
more harm than good.

Soil Quality Test Kit

Dr. Weil has developed an inexpensive, easy-to-use kit to help farmers
determine the active organic matter fraction in their soil. Remember that,
when soil is mismanaged, active organic matter is the type that is lost
first. Farmers can use the test to determine which of their fields needs the
most work. Using the kit, you can mix together a solution of potassium
permanganate with soil, then use the color of the solution to determine
active organic matter. The test kit isn’t yet available commercially, but the
details of what is in the kit and how to use it will appear in the first
issue for 2003 of the American Journal of Alternative Agriculture. The only
expensive component is the hand held colorimeter, sold by HACH, Inc., for
about $200. You could also use a color chart for much more approximate
comparisons. Everything else should cost less than $20. The NRCS Soil Quality
Institute is still deciding how to make it available.
--------------------------

paul tradingpost@lobo.net






  • [Livingontheland] Dr. Ray Weil - Let's talk about soil, Tradingpost, 07/15/2008

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