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Subject: Healthy soil and sustainable growing

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  • From: "Tradingpost" <tradingpost@lobo.net>
  • To: livingontheland@lists.ibiblio.org
  • Subject: [Livingontheland] from another list
  • Date: Tue, 08 Jul 2008 22:32:37 -0600


I replied to a post on another list, below.
--------------

I have to critique Caldwell's article. First, most of his final
recommendations seem sound. But some of the explanations and conclusions seem
unsupported at best. Words like "problem" and "overloading" imply harm beyond
what his evidence shows. My comments interspersed.

paul tradingpost@lobo.net

*********** REPLY SEPARATOR ***********

On 7/8/2008 at 8:39 PM Joel Gruver wrote:

>Hello folks,
>
>In the process of writing an article on nutrient management for organic
>vegetables over the last 2 days, I have been looking back at some of my
>favorite articles (technical and non-technical) on the subject.
>
>Copied in below is an article that I think is a nice discussion of how to
>build soil organic matter without overloading soils with nutrients.
>Perhaps some of the ideas will seem like deja vu if you've been reading my
>posts on this
>subject :->. Sorry about the formatting.
>
>Joel
>
>BTW The author is an organic farmer, extension educator and friend from
>when I farmed in New England.
>
>******************************
>How Can Organic Vegetable Growers Increase
>Soil Organic Matter Without Overloading the Soil with Nutrients?
>
>by Brian Caldwell
>Cornell Cooperative Extension Educator
>South Central NY Area Vegetable and Fruit Program
>
While this is a beneficial practice in the short
>term, in the long run it can lead to over-fertilization
>and water pollution. The problem is similar to overfertilization
>that occurs on livestock farms with insufficient land on which
>to properly spread their manure.

Yes, spreading fresh manure too heavily over time can create specific
problems. But spreading excessive non-manure compost may not harm crops or
pollute the water at all, due to lack of salts in manure.

> In fact, if manure or
>compost is added specifically to increase soil organic
>matter levels, which is a goal for many organic
>farmers, then usually all nutrients will be added
>beyond crop requirements.

We need to be clear whether we're talking about harmful levels of nutrients
or just wasted excess, and whether excess (once additional excess is stopped)
is ever wasted if it continues to feed crops.

>Let’s look at an example from my own farm. “Field
>1” is a small field of about 1/5 acre which had been the
>farmstead garden for many years before I moved to
>Hemlock Grove Farm in 1977. It had higher nutrient
>levels than our other fields. I have soil test data (Table
>1) from this field over a period of 21 years, starting in
>1978.

>Table 1. Soil Test Data, Field 1
>This data shows the problem. Soil nutrient levels are
>all in the high range after 21 years, which seems good,
>but if I continue the same practices, they will get too
>high.

He added excess for 21 years? Well, I don't think we have to worry about very
many people being so foolish, so this extreme example proves ... what?

>Phosphorus levels are already very high, and
>going up faster than anything else. ... High soil P does not hurt
>crop plants, but can contribute to water pollution.

High soil phosphorus doesn't hurt the crops? Good. Let's stop trying to solve
a problem that doesn't exist. Water pollution? From excessive manure or
compost, or from commercial superphosphate? Makes a big difference, doesn't
it. BTW chicken manure will build up too much phosphorus over time.

>The field did not seemingly get heavy applications of
>organic fertilizers, averaging only 6 tons per acre per
>year of beef or sheep manure, with occasional additional
>applications of hay mulches, commercial and
>homemade compost, and wood ashes. (In retrospect,
>the 500#/A of rock phosphate we put on one year
>looks like a mistake.)

Whoa! He added all that phosphate and wood ashes, and then uses the fact that
those nutrient levels were excessive to support his argument against
"overfertilization" with compost and manure? How much wood ashes? Not told. I
hope he didn't try to use this as a Ph.D thesis.

>Where do excess nutrients go? Extra added P and K
>are mostly held in the soil in unavailable forms, but
>most nitrogen is not...
>... most (over 1500#/A or about 70#/A/year in this case)
>of the excess nitrogen will not be held in the soil, but
>will leach into groundwater or volatilize into the air.
>In many situations, such as typical home gardens, this
>is not a problem, since only a relatively small amount
>of nitrogen is in question. But if this practice is done
>on a widespread basis or on large farms, there is
>potential for significant groundwater pollution. The
>same situation occurs when excessive chemical
>fertilizer is applied.

No, it's not the same. Nitrogen bound up in added and decomposing organic
matter doesn't pollute groundwater on the same scale as commercial N. Of
course 95% of anhydrous ammonia is lost to the air.

>I believe that there is no good reason to continue to
>increase these soil nutrient levels.

No more rock phosphate or wood ashes? Duh!

The field produces
>good yields and quality. It has clearly reached a
>“mature” stage in which heavy applications of
>brought-in organic materials are unsound...
>How do we raise soil OM levels without causing this
>problem?

Problem? Who else but Caldwell would add such extreme excess for so many
years? And didn't he just say it wasn't hurting the crops at all?

>High levels of soil organic matter are desirable in
>many ways. Higher OM improves soil water holding
>capacity, aeration, infiltration, nutrient holding and
>release, and more. But how do we achieve high soil
>OM sustainably over the long term? And how high
>should it be?

Fair question.

>Virgin soil had much higher organic matter levels than
>current cultivated soils. How did high soil organic
>matter levels arise naturally (presumably, without
>groundwater pollution)? The answer is: very slowly,
>and in the absence of tillage and crop removal.
>Intensive tillage is the primary culprit in “burning up”
>soil organic matter at a very high rate, requiring that
>we add outside sources of OM to the soil. Under
>natural, untilled forest or prairie conditions, highly
>carbonaceous organic litter (leaves, etc.) is added to
>the soil surface each year, and roots die within the soil.
... soil organic matter can build up very gradually
>over thousands of years, to levels around 10% in many
>virgin mineral soils...
>When this land is cleared and repeatedly tilled, OM
>levels drop rapidly down to less than 2% in the
>absence of manure or compost applications. A sick
>soil. But remember, our real goal for a farm field is to
>preserve or increase soil quality, not just its OM
>content. We tend to be in a frame of mind that says,
>“the more OM, the better.” While there is some truth
>to this, under any given tillage and cropping regime
>there is an “equilibrium” level of soil OM. Generally,
>the less tillage, the higher this equilibrium level. OM
>levels can be maintained above equilibrium only by
>continuous heavy applications of compost or manure
>that carry far more nutrients than the crops can use.
>This is wasteful and leads to pollution over the long
>run. (The Biodynamic goal of the farm as a self contained
>organism helps to avoid this problem,
>because it discourages importation of large amounts of
>nutrients.) Research at the Rodale Research Center
>has shown that soil biological activity, quality, and
>fertility can be very high, even at modest (2.5-3.0%)
>soil OM levels, if large portion of the OM is in the
>“active” form, i. e. in the process of being broken
>down. So, the key soil quality strategy in farming is
>not merely accumulating a high soil OM level, but
>cycling it rapidly and effectively. It is counterproductive
>to shoot for virgin soil OM levels on tilled farm
>fields.

Good.

>It is important to realize that the constant production of
>tilled crops, especially vegetables which return few
>residues to the soil, is the harshest way to treat your
>soil.

Very good.

Sod crops in rotation are the only tried and true
>way to increase long term soil OM levels without
>negative “side effects.”

But he hasn't established that excessive compost/manure actually produces
negative "side effects" - other than wasted excess. He implied it but that's
unsupported. How must know that people have used lots of compost or manure
for many years to raise soil OM without harm to their crops.

>Sod accomplishes this because
>the soil is not tilled, and extensive root systems are
>formed. Traditional field crop rotations often involved
>applying manure or compost to a field only once in
>every 4- or 5- year cycle. (A typical example is Corn-
>Small Grain/Hay-Hay-Hay, with manure applied
>before the corn.) Organic matter levels and soil
>nitrogen were greatly enhanced by at least 2 years of a
>sod hay crop. Phosphorus and potassium did not build
>up in such systems, but were instead mostly cycled
>around the farm through feed and manure.
>An ideal rotation for vegetable growers, from a soil
>and nutrient standpoint, would be to substitute vegetable
>crops for the heavy feeding (field corn) and
>light feeding (small grains) crops in this traditional
>rotation. Heavy feeding vegetable crops would
>include intensive greens, brassicas, sweet corn, leeks,
>cucurbits, etc., while light feeders would be root crops,
>beans and peas, etc. A sod crop of legumes and
>grasses will provide a maximum OM contribution,
>while supplying its own nitrogen. If hay is harvested,
>there may be a net removal of P and K. These nutrients
>can then either be sold off the farm, or fed or
>otherwise recycled within the farm.

(skipping wood chips)

>So, what are the take home lessons here? Mine
>are—
>1. Significantly increase the sod and light-feeding
>crops in your rotation on “mature” fields.
>2. Reduce tillage and keep soil covered with cover
>crops and mulches.
>3. Don’t waste nutrients by excessive manure or
>compost applications. This is particularly
>important if your P levels are in the “high”
>range. Rely more heavily on getting nitrogen
>from legume cover crops and sod than from
>manure or compost.
>4. If you want to increase soil OM levels further, try
>experimenting with spreading wood chips on
>your fields in moderate (10T/A or less) amounts.
>They can be spread just before spring tillage, or
>even more effectively, left as mulch on the
>surface until next spring.

I'll agree with most of that. But it's unlikely phosphorus would be too high
unless there's a lot of phosphate (or chicken manure) added over a period of
years. Which is exactly what he did. The wood chips business is too vague and
unsupported to go with that.

Caldwell's an extension educator? Cornell can do better. I'd give him a D- to
be charitable.

paul tradingpost@lobo.net








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