On Tue, 6 Sep 2016 11:51:13 -0400, Frank wrote:

Horse manure can often contain harmful pesticides used to keep down
flies in the stable. Knew an organic farmer that would not use it.

Horse manure is too much for two five-gallon buckets of soil, so, I am
sorry for misleading folks.

I'm mostly asking for *technical* details like how I know if the soil is
good or bad in the first place.

I did look up how plants get their nutrients.

Apparently only about 1% of the root actually *touches* nutrients, which
soak into the root along a corky layer that surrounds each root cell. That
corky layer utilizes ATP to *force* the nutrients into the cell since there
is a *higher* concentration inside the cell so simple osmosis won't work.

However, 99% of the nutrients get *to* the roots by osmosis of the
fertilizer. That is, if I put a nodule of fertilizer a few inches away from
a root tip, the root can't get to the fertilizer until the nutrients
*diffuse* out by simple osmosis from the nodule to the root.

So, what seems to happen is that a *water flow* is set up where the leaves
transpire water, which then causes a vacuum in the root which pulls in
water by pressure, where that water flow brings the water close to the root
where that water contains the fertilizer nutrients that diffused by osmosis
into that water.

Once the water is pulled next to the root, then an active (and complex)
process begins to actively pull the nutrients into the cell.

That's as far as I got, so any added value you can provide as to the
technical process of fertilizing a bucket of soil would be helpful as the
goal is for the kids to learn how the whole process of growing food works
(scientifically).