David Hare-Scott wrote:
David E. Ross wrote:

The purpose of compost is to improve the structure of the soil, not
to provide nutrients. Since compost is often applied only to the top
inches of the soil, you should want any nutrients -- as few as there
might be -- to leach down into the root zone. Inhibiting the
leaching of nutrients would thus be counter-productive.


Compost supplies (directly or indirectly) organic colloids eg humus,
that have a role in binding ionic nutrients It also improves
drainage and tilth. All that is part of improving structure, that is
improve the way the soil acts to allow nutrients, air and water to be
available to plants. Also compost does supply some nutrients for the
plants and some for the micro-organisms as well as directly supplying
some useful microbes.
So isn't it fair to say compost supplies nutrients and improves
structure?

i think so, that is why i'm considering doing it and adding
it to my pile, because i want my top layer of added mulch/compost
to contain beneficial microbes to help counteract the negatives
i already have established. in effect i'm trying to cure fungal
troubles that are already established by getting some competing
bacteria back into the mix. i think they've gotten baked out
because there is so little organic matter in there as it is right now.
i want to give them more surface area to colonize and have
more nooks and crannies to hide in when the hot weather
comes along. considering what i've already got it really
isn't going to hurt.


Excessive leaching is a real PITA. I worked on a sand-based garden
for 20 years and unless you were constantly replenishing organic
matter and nutrients it had very poor productivity except for the
natives that were adapted for poor soil. I will bet that most of the
soluble nutrient ended up in drains and then waterways soon after it
was applied.

i'd have amended with clay. i keep trying to trade clay for
sand to people around here but they seem to prefer to water
instead.


Now I have a clay-silt based garden and it is extremely productive
after only a couple of years. Having that clay colloid there (as
well as organic matter and compost) greatly reduces nutrient leaching
so that I can grow intensive crops with good productivity and only
add manure once or twice a year.

our productivity here is great too. i have two cherry tomato
plants that are about 6 ft across and 5ft high each. we really
should not have planted them at the ends of the regular tomato
garden as they have made it almost impossible to get in there to
harvest and have blocked most of the light and air...

we don't add manure but we do bury all debris and rotate
beans through. added sand and organic matter helps if i have
any handy, but i usually don't unless i've been thinning or
trimming.


I think the way that it works is during rain events or deep watering
the colloids on top (near where the manure is applied) becomes
saturated with bound ions and so the excess is carried down to the
root zone and then to the subsoil which ultimately gives those
regions a chance to bind ionic nutrients too. Despite the
difficulties with drainage sometimes, I will take the low leaching
silt before the high leaching sand every time.

after hearing what some people around here go through in
the hot summers having to water every day or every other
day, i'd agree. it's a bugger to weed when it's dry though and
i was tilling concrete the other day (9hrs in 90degree weather,
but we'd finally had some rain so it was time to get that job
done so we could force the next round of weeds to sprout and
then have it ready to plant for the spiral garden).


songbird