Ray Weil's classic textbook,
The Nature and Property of Soils, is available
from most college bookstores and internet booksellers
for between $85 and $105 (about 10 cents per page).
Amazon.com carriers several useful reader reviews
of the book. Ordering information:
The Nature and Properties of Soils, 13th Edition
By Nyle Brady and Ray Weil
Prentice Hall, Upper Saddel River, NJ
Publication date: 2002
Available online from Prentice
Hall for $94.50.
The Soil Biology Primer is an
introduction to the living component of soil and
how it contributes to agricultural productivity,
and air and water quality. The Primer includes
units describing the soil food web and its relationship
to soil health, and units about bacteria, fungi,
protozoa, nematodes, arthropods, and earthworms.
Originally published by the NRCS, it is now available
online at their website, or you can purchase
copies from The
Soil and Water Conservation Society.
To order by phone:
To order by e-mail: email@example.com.
Cost is $11 plus $5 for shipping and handling.
Iowa residents: Add 6% sales tax. Canadian residents:
Add 7% GST. Multiple discounts available.
At A Glance
The Groff’s Cedar Meadow Farm is a good
example of soil building and soil preservation
in action. In the early 1980s, Steve Groff stopped
tilling on about 15 corn acres, "because
we had some erosion problems and I didn’t
like having to fill in gullies before harvesting
corn." Since then, Steve has fine-tuned his
own brand of no-tillage on his 175-acre family
farm in Lancaster County, PA.
Relying on three components—cover crops,
intensive crop rotation, and long-term no-tillage—Steve
has measured his progress: organic matter went
from 2.7% to 4%; soil aggregate stability is at
67% in untilled fields, compared to 16% in recently
tilled fields; soil erosion has been cut from
14 tons per acre per year to almost nothing; and,
soil microbial biomass has tripled.
Farm name: Cedar Meadow Farm
Location: Lancaster County, Pennsylvania,
near the Maryland border
Important people: Steve and Cheri
Years farming: 3rd generation
farmer on same farm
Acres tilled: 175
Soil type: Loam
Crops: Corn, alfalfa, soybeans,
broccoli, tomatoes, peppers, pumpkins, annual
Livestock: 70 head of steers
and a small bison herd
Regenerative farm practices:
A rotation heavy on ground covers and reliant
upon no-till planting. Steve no-till plants his
cash crops into a thick vegetative residue.
For more information:
Ray Weil at a field day last summer,
picking apart the secrets of healthy
soil with a hunting knife and his wit. Ray is
a professor of soil science at the University
of Maryland and co-author of The Nature and Properties
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
“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
- 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
- Limit or eliminate herbicides and pesticides in order
to encourage natural cycles of pest control.
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.
first. Roots are the way to go. You want to plant cover crops
with a lot of roots, and then leave the roots underground.”
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
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.”
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.
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.