> We are putting in 3,400 ft of underground irrigation lines
> and it has been fascinating to see what the soil profile
> looks like across several different fields.
Steve, your post, and the compost I was shoveling on Saturday reminded me of
a question on the soil/plant relationship I have wondered about for a long
time: What is the effect and value to the plant from (sub-meter) spatial
heterogeneity in the soil?
The compost I was using was mainly 1997 oak leaves. The leaves were packed
and mostly dark and friable, interlaced with fungi and roots, with a deep
mushroom odor. Along with the leaf mold were sticks up to an inch in
diameter in various stages of decay. I put a large amount (about 10 bu on
150 square feet) because the bed really needed lightening up. I did my best
to mix the compost in, but the soil is very heterogenous now. As roots
explore this, they are going to find many diverse microenvironments.
Aside from the difficulty of getting a good seedbed in this, I imagine this
heterogeneity is good for plants. Even if the net characteristics of the
soil would reduce availability of certain nutrients, the spatial/chemical
diversity of the medium will insure that some part of the root system can
find whatever the plant needs.
This is why banded fertilizer application is so successful at getting P into
the plant even under conditions conducive to P fixation. Roots grow into
the region of nutrient availability. Perhaps one of the values of no-till
is stratification of the profile into chemically distinct zones. Beneficial
effect of heterogeneity could also be a rationale for incorporation of raw
organic matter in minimum-till systems (a little like my garden bed). Zones
of decaying residue might provide a more complete smorgasbord for plants.
Other situations where spatial heterogeneity might be important include
places where the subsoil has anion-exchange capacity, and under
I found a few relevant abstracts I'll send you two personally (if anyone
else wants them, let me know).
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