>I'd be interested in learning what
>it is that is more beneficial about composting in-situ - in the soil -
> as against ahead of time. Evidence from the literature?
>
Hello Ann.
I don't think this applies to raw manure or even compost there has been
evidence in Latin America for many years that the break down of raw organic
matter (e.g. straw) in the soil is more beneficial for soil structure than
in the compost heap. There was work done in Argentina and Brazil decades
ago on this which has led to a whole theory of soil structure in tropical
soils.
I think this work has been mostly ignored in the North, as is most Latina
American research, but scratching around there was something published by
Molina in English that outlines the theory the aerobic decomposition of
cellulose in the soil by Spirocheta cytophaga releases a 'microbial gel',
polysacharides that contribute directly to the formation of humic colloids
and crumb stucture. (Molina & Sauberán "Cellulose Bacteria and Soil
Conditioners" Journal of the Soil Association, January 1956: 415-17).
'Aerobic' means straws layed out as mulch; straw plowed into the soil
(resulting in largely anerobic decomposition) does not have this beneficial
effect. According to Ing. Jorge Molina (personal communication), symbiosis
of the bacteria with an amoeba and a fungus may be important in this process.
What is more exciting is that these and other researchers found that, apart
from the effect on soil structure, this decomposition provides a substrate
for non-symbiotic N fixation, principally by Azotobacter sp., which in some
experiements was found to increase many fold and supply N in quantities
comparable to heavy doses of synthetic N fertilizer. The original discovery
of this phenomenon is actually attributed to Winogradsky. Naturally,
supplying N in the form of soluble synthetic fertilizers in these
experiements totally supressed the Azotobacter increases. This research is
difficult to find but some of the early work is described in a Latin
American classic called "Manejo Ecologico do solo" Livraria Nobel, Sao
Paolo, Brasil. First published in 1980 it was in its 9th edition last I
knew. It has been translated into Spanish, but not, as far as I know, into
English.
All this refers to raw OM, not raw manure, which requires a completely
different management approach (composting, for example)
Combing the recent US literature on soil microbiology I have only found
oblique references to this process of cellulose decomposition and soil
structure and no discussion of the details, i.e. Spirocheta etc. In this
SANET thread there are also several intriguing quotes along these lines
For example Joel Gruver decribes his research:
>My focus was on soil structural effects... in a nutshell, the process
>of decomposition/microbial activity is very important to aggregate
>formation and stabilization... a majority of studies seemed to show that
>more labile organic substrates had greater formation and stabilization
>effects (both short and long term in some cases) than materials that were
>more recalcitrant like a mature compost...
>
And how about this morsel provided by Steve Diver:
> "For improvement of physical properties of soil, actual decomposition
> in the soil, rather than composting, is best because polysacharides
> are produced from carbon compounds that would otherwise be lost in
> composting. These natural water-soluble polymers do much to create
> and stabilize the soil aggregates to give good physical properties to
> soil...
>"Although there are good reasons for composting, the idea can be
>wrong much of the time. Since 75 percent, more or less, of the
>organic carbon is lost in composting, little remains for real
>improvement of the soil structure. When possible, direct application
>avoids this problem. The value of organics for soil improvement
>comes mainly from carbohydrates. Carbohydrates are mostly lost in
>composting. Some users assume that the composting process results in
>the production of biostimulants; uncomposted materials applied to
>soil can result in the same."
>
>From:
>Wallace, Arthur and Garn A. Wallace. 1995. Compost and composting:
>facts and myths. p. 39-51. Soil Conditioner and Amendment
>Technologies, Volume 1. Wallace Laboratories, Los Angeles, CA.
>335 pp.
>
In the tropics this is particularly the case. Compost has its uses, but fot
the most part, especially in soil restoration, compost is just too much
work for too little effect to be useful. Try and convince some European or
American organic certifier of this though...For many people composting is a
sacred act and you just ain't organic without it. The fact is mulches,
green manures and good ol' natural succesion (sometimes called weeds) are
often far more effective.
Steve Grof confirms what Nebraska farmers have told me:
>I have observed, on my farm, that much of the above information is
legitimate.
>Soil aggregate stability is what I've noticed as one of the great
improvements
>resulting from leaving the residues on the soil surface to decompose.
Doesn't
>this information build a strong case for the benefits of no-till?
>
I would say yes to the last question--unless no-till to you means poisoning
the soil biology by spraying Round-up or some other noxious biocide instead
of mowing. But many farmers recognize the benefits of leaving the residues
on the soil surface (aerobic conditions) rather than plowing them in or
burning them.
I have a long list of quotes such as the Wallace's but very little good
references to research on the actual processes going on that would give us
clues as to how to manage soil condition to increase colloid formation,
stimulate free-living N fixation, P mobilization etc.
All of this has tremendous implications for designing strategies to recover
soil fertility on thousands of hectares of soils in Latin America destroyed
by poor grazing practices, improper buring and herbicides. Ag companies are
always ready to come in with chemical solutions that totally ignore the
fact that it is biological factors that are limiting productivity on these
soils. Can anyone provide some good references on the microbiology of this
process?
Ronald Nigh
Dana, A.C.
Mexico, D.F. & San Cristóbal de Las Casas, Chiapas
Tel. y FAX 525-666-73-66 (DF)
529-678-72-15 (Chiapas)
danamex@mail.internet.com.mx
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