Back in 1998, Joel Gruver made the following post to SANET:
Hello to all...
focus was on soil structural effects... in a nutshell, the process
issue of differences in carbon sequestration was not discussed in many
literature sits almost finished somewhere in Dr. Weils office... I
Other folks joined in, including Steve Diver and Cary Oshins; this was the post that seemed to get things started:
> Dan Hemenway wrote:
the topic on sheet mulch composting in place versus composting
benefits and uses of compost as a stable humus product
came across the following Sanet post by Ann Clark back in 1995,
>From: "E. Ann Clark, Associate
to Dick R. on the issue of composting. Just curious about
points on "waste" management at landfills! Ann
Steve Diver’s follow up post added the following points:
“There's a little-known but valuable publication
of the articles titled "Compost and Composting: Facts
people think that making compost is to create fertilizer.
to decrease the volume of waste, especially for going into
improvement of physical properties of soil, actual decomposition
Recently I have been having a discussion with Dave Schellinger over on the USCC list (compost list) concerning this very matter. Mr Schellinger put forward the view that raw organic matter actually decreases aggregate formation in the soil, and cited some literature claiming to support his point:
“Humus binds clay particles, but raw organic matter disperses and
reduces aggregates. Bohn, et al., 2001, points out that greater
aggregation produces less stable organic matter contents in soils due to
increased aeration and microbiological degradation. Even aggregates
become less stable with added organic matter. This coincides with my
statement that raw organic matter additions reduces ped formation. Approximately
50-80% of fresh organic matter is lost from most temperate soils in the year of
application, just like during the composting process. And, the smaller
the particle size, the faster the degradation occurs. If more organic
matter is added to the soil, it degrades faster. The book points to an
Schellinger also put forward the proposition that the addition of raw organic
materials to soils increased production of various greenhouse gases, aside from
CO2, compared to composting prior to soil application. In large part I think he
based this on the risk of flooding and excessive rain; his location in
I put forward the counter proposition, that raw organic residues could well improve the greenhouse gas status of a soil, if they resulted in improved soil structure and subsequent improved plant growth. The importance of seeing the full picture of these scenarios is great, I believe. I would certainly appreciate input from Joel Gruver and others concerning our current understanding of these matters. I did cite in our exchange the work of Dr Fred Magdoff, who actually compared two scenarios of manure management and found direct application of manure to yield better aggregation than composting the manure first:
It should also
be noted that no tillage scenario I am aware of allows for a sustainable return
to uncultivated SOM levels without heroic applications of organic matter, and
this because tillage is itself a major destructive force against SOM. However,
by using rotations including several years of proper pasturing soil can be kept
The question of ‘to compost, or not to compost’ hits farmers squarely in the face, especially those whose livestock are fed exclusively or nearly so from the farm acreage itself. One factor we did not discuss is the issue of transportation costs and the mechanical costs of composting, which obviously also have greenhouse gas consequences. Labor time savings for the farmer are also an issue. This is less of an issue where manure producers rely on transported inputs and generate large quantities of manure which must subsequently be retransported substantial distances; there the calculus should favor composting on shipping cost grounds quite strongly. Of course, the farm’s overall crop diversity and the need for mature, relatively weed free compost for specific crops are also factors which the decision maker needs to consider.
I actually experience an opposite situation. I have access to large quantities of shredded compressed dry fall leaves. In my view it clearly seems favourable to transport these as is to my growing site prior to application, rather than composting them first which would mean the addition of a substantial amount of water, as well as requiring space which at present is unavailable. This might be analogous to the handling of hay, which when dry and bailed can be transported more cost effectively than if it were composted and moist. There remains the issue of whether to compost prior to soil application, of course. With hay the issue of weed seeds looms large, for any future open soil growing; even with leaves there is some potential for weed seed presence.
I consider that the use of these leaves both as mulch and as incorporated organic matter will predominate in the mixed vegetable, small fruit and tree orchard context which I participate in. Doubtless some will also be thermally and worm composted as well, to produce materials for compost teas and watery extracts as well as direct applications. I believe that my sandy soil will benefit from direct decomposition of the leaves and subsequent fungal growth in the soil itself more than if all the leaves were composted before application. Because this soil is very well drained I anticipate no serious anaerobicity problems leading to methane or NOx production as a result. In more poorly drained soils that experience spring and/or fall flooding, it could very well be wise to compost and apply shortly before planting, or as crop choices permit, to apply after danger of flooding is past but with sufficient time to decompose prior to planting.
I would appreciate any specific or general comments on these subjects. I can make the full text of the exchanges between myself and Mr Schellinger available to anyone interested.
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