Healthy soil and sustainable growing

["Tradingpost" <tradingpost@lobo.net>]

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