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Re: Humus -- rural -> urban -> rural
Ann, you pose the question:
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?
The direction I'm speaking about in management of manure may be different
in the "north country" where you're working. I'm referring to the role of
dung beetles, earthworms, and such. The dung beetles can bury 6000 lbs
fresh manure per acre per day, from the estimates of Walt Davis, a
colleague in southern Oklahoma, when he begins managing his livestock to
avoid poisoning the invertebrates in the soil -- grazing plans that break
lifecycles of parasites without pesticides -- and the dung beetle
populations build up as the soil temperature reaches 50 degrees F or
thereabouts. There are no piles of manure after two days! The result is
that the soil health and vegetation really jump, and toxicity is not found.
We also tested raw sewage and the dung beetles went for it with great
vigor, but the treated sewage (biosolids) was not palatable. This is no
surprise, since the treatments required for "health reasons" are partly for
reduction of smell and attraction of flies. For treatment of sewage, most
of the proteins have been converted to ammonia, and the same loss holds for
readily available carbon. Further, composting causes a net loss of organic
matter that soil organisms can use, but the organisms have to be present in
the soil in suitable numbers and have conditions favorable for matching
their growth and utilization with the amounts of uncomposted materials
applied. This requires good management, matching the supply with the
demand, so to speak.
If we look at the sewage as microbial and invertebrate food, and we are
trying to increase these populations in the soil, then there surely will be
some balances needed to avoid over-doing the application, which you pointed
out. If we dump even good stuff on at the wrong time or in the wrong
amounts, then we certainly can expect problems. The direct metering out by
livestock as they are grazing helps stay "within the window". Bringing
urban equivalents to the rural sites doesn't have such a built-in meter.
In Austin we have had land applications of biosolids for several years, and
other locations, such as near St. Paul, MN have injected biosolids before
de-watering. It's been fine for corn and great for the land in general.
However, it seems to me that the key is blending the return process of such
resources into the needs of the soil organisms.
In another recent post, Karen Grobe commented
"... All farmland should not receive compost. Some farmland is used to
produce cattle, and it would not be appropriate to use compost ... on
grazing land."
I would disagree to the point that sometimes compost (or biosolids) may be
needed to "jump start" to get grazing land into a good state of health.
The importance for the soil health may be less in terms of the production
of "food" products than in the fact that it is watershed. If land managers
are able to increase infiltration rates and water holding capacity
sufficiently, we see springs return to perennial flows, and watertables
high enough to maintain perennial vegetation (grasses and others) in
healthy states even during drouth conditions. However, if properly
managed, grazing land (pasture or rangeland) seems capable of improving and
remaining healthy through the recycling of organic matter from the
livestock alone. Certain minerals in certain soils, however, may be
another matter.
R. H. (Dick) Richardson Office: 512-471-4128
Zoology Dept. Home: 512-476-5131
Univ. of Texas FAX: 512-471-9651
Austin, TX 78712