Gardening Articles for week ending 24th MAY 2008
by Wally Richards.
TO DIG OR NOT TO DIG?
Taking a slightly altered
quote from Shakespeare; To dig or not to dig, that is the question?
is one aspect of gardening that has not really been thought about by many gardeners.
digging or tilling the soil has been going on for about 10,000 years (more so
in the last couple of hundred years) and the only two factors that I can see reasons
for doing this are; To clean up and bury whatever is currently growing on the
bit of dirt we wish to plant out, whether this be weeds, a cover crop or the remains
of a past crop.
The other reason would be to open compacted soils that have
been flattened through our walking on the area or stock doing the same.
is the suggestion that by digging and turning over the soil, we are bring to the
surface nutrients that are in the sub soils. If we have good earthworm populations
they are already doing this job for us and providing nitrogen from their slime,
something our spade is incapable of doing.
There are more reasons why we should
not dig our soils than there are for doing so.
The first and most obvious is
that it is hard work unless one is younger and really fit.
If the top soil
level is shallow and there is a hard clay base beneath, then from my experience
it is damn hard work and you end up with a lot of clay lumps on top which have
to be broken down before they turn to concrete in the dry times.
I used to
dig gardens in days gone by till I obtained a rotary hoe and used that to cultivate
the soil, I now realise that I wasted a lot of time and sweat, doing damage to
the soil life and gaining little advantage.
From the Internet at http://ohioline.osu.edu/aex-fact/0510.html
Soil carbon sequestration is the process of transferring carbon dioxide
from the atmosphere into the soil through crop residues and other organic solids,
and in a form that is not immediately re-emitted. This transfer or sequestering
of carbon helps off-set emissions from fossil fuel combustion and other carbon-emitting
activities while enhancing soil quality and long-term agronomic productivity.
Soil carbon sequestration can be accomplished by management systems that add high
amounts of biomass to the soil, cause minimal soil disturbance, conserve soil
and water, improve soil structure, and enhance soil fauna activity. Continuous
no-till crop production is a prime example. Cultivation of the soil releases
Here is another interesting fact:
The estimated amount
of carbon stored in world soils is about 1,100 to 1,600 petagrams (one petagram
is one billion metric tons), more than twice the carbon in living vegetation (560
petagrams) or in the atmosphere (750 petagrams). Hence, even relatively small
changes in soil carbon storage per unit area could have a significant impact on
the global carbon balance.
Carbon sequestration in soils occurs through plant
production. Plants convert carbon dioxide into tissue through photosynthesis.
When we dig our gardens we release carbon dioxide into the atmosphere and contribute
to global warming. Another good reason not to dig.
In our soils there are at
least 10,000 living species and more than 1 billion individual bacteria in 1 gram
of soil (Torsvik et al. 1990). There is a massive, complex, microscopic world
in our soils which we call the soil food web. Beneficial fungi attach themselves
to the roots of plants and send out threads into the surrounding soil to gather
moisture and nutrients, which they then supply to the plant in exchange for some
carbohydrates (sugars) This intimate, mutually beneficial relationship is one
of the key aspects of healthy plants as the fungi can increase the available moisture/nutrient
catchment area by about 800%.
This web of strands grows in healthy soils and
interlinks the roots of other plants to each other like a great road or railway
system linking small towns (plants) to each other. Likely this is one of the reasons
for companion planting as two plants that are compatible will provide each other
better growth or protection aspects, through the web system.
When we dig the
soil or pull out a plants, roots and all, we break up millions of these chains
to the decrement of the whole system. Besides not digging the soil we should ideally
not pull out plants or weeds but cut them off with a sharp knife just below ground
level. By doing this we do not disrupt the web and the roots will decay giving
further nutrients to the soil and plants. The foliage should be left on top of
the bare soil to further build up your humus or top soil.
We also can increase
the soil activity (bred more soil life) by applying things like liquid manures,
worm pee, Mycorrcin (which is a special food for this purpose). What we should
not do is apply chlorinated water, chemical fertilisers, chemical sprays and herbicides
to the gardens as these poisons kill what we need to protect and nourish. Also
we should not dig or walk on our gardens.
It is easy enough to create garden
plots especially if you make raised gardens with wood or concrete blocks of a
width that is suitable to work each plot from the sides.
This is also a great
way of overcoming the problems of heavy clay soils or light sandy soils.
what is underneath as you will be gardening well above that level.
I made a
raised garden at the beginning of the year using corrugated iron and 100 x 100mm
The posts were tanalised so I gave them coats of acrylic paint to seal
the chemicals in.
I made the posts the same length as the width of the corrugated
sheets and did not bury the posts in the ground. Simply drilled and screwed the
sheets to the posts and have the structure just sitting on top of the soil.(Note
iron sheet length used was 1.8 metres and the third sheet was cut in half for
the two ends)
As I can walk around the whole structure it is easy to work it
from all sides. One full side of iron is facing in a northerly direction to catch
the sun which warms the contents.
Now the depth of a width of a sheet of iron
makes for a fairly deep structure and the problem is to fill it
up to a suitable
height for planting up.
I had an amount of weeds, bracken, blackberry foliage
and branches which I placed in the bottom of the raised garden and trampled it
Compost from my bins which would contain weed seeds was placed on top
Next went in used compost from container plants that had finished,
bringing up the level nicely.
This was followed by wet newspaper and cardboard
on top of which I placed a good layer of animal manure.
Worms and worm casts
from my worm bins followed along with a good dose of worm pee.
A few bags of
new and purchased compost was used to cover this and then the minerals were applied
such as; Rapid Lime, Ocean Solids, rock dust and Magic Botanic Liquid (MBL).
finish off more purchased compost was used bringing up the level of material about
30cm from the top of the structure.
I then planted some seeds of carrots, spring
onions and dwarf beans and a good number of silverbeet seedlings. All watered
in with MBL and filtered water (to remove the chlorine)
As the iron made a
heat trap the seeds soon germinated and the silverbeet surprised me in the speed
of growth. From very young seedlings to the first harvest of outside leaves was
only 4-5 weeks.
The dwarf beans started producing pods to harvest a couple
of weeks later.
Way to go.
Problems ring me
at 0800 466 464 (Palmerston North 3570606)
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