manufacturing topsoil

manufacturing
topsoil
Compost has proved effective for manufacturing organically-rich
topsoil from poor quality soils, sub-soils or other inert materials.
The result is a superior substitute for natural New Zealand topsoil
which is often difficult to obtain.
Compost provides organic matter essential for soil health. Chemical,
physical and biological properties of the soil are improved, increasing
its range of applications.

manufacturing topsoil
Methods
Blend compost into existing
soil (in-situ)
Blend compost into
stockpiled materials (ex-situ)
Benefits of using compost
▸ Improved soil structure & tilth
▸ Improved water holding in light soils
▸ Reduced bulk density in heavy soils
▸ Macro and micro plant nutrients supplied
▸ Increased soil cation exchange capacity
▸ Reduced cost of topsoil necessary for the project
▸ Improved soil microorganism activity
▸ Protection against erosion
▸ Improved visual appearance
▸ Buffered soil pH
Manufacturing to suit
Topsoil manufactured with compost should be suited for
a particular application (e.g., landscaping vs. sports turf
establishment) and crop (e.g., vegetable garden vs. grass). Soil
characteristics such as pH, electrical conductivity and texture
should be taken into account. The existing site soil, and other
materials used, should be tested to evaluate their characteristics.
The final manufactured topsoil should be analysed to verify its
characteristics.
Blending
The application rate of compost needed to improve the organic
matter content of a soil can be determined. For instance, blending
65 to 84m3 of moist compost having an organic matter content
of 30% on a dry weight basis, with 100m3 of soil, would raise the
organic matter of that soil from 2 to 5%.
Transforming a droughty soil into a
productive one using compost.
1 2 3 4
pH 4.4 5.9 6.9 8.3
Organic matter % 1.1 5.1 9.2 23.4
Soluble salts (mmhos/cm) 0.07 0.36 0.70 1.52
Water-holding capacity % 25 39.5 54.9 80
TKN (% dw basis) 0.04 0.05 0.10 8.59
P 2
O 5
(ppm) 41 160 330 2500
K 2
O (ppm) 58 214 461 3200
1 - Existing soil (sandy)
2 - Soil : Compost 3:1
3 - Soil : Compost 1:1
4 - Compost
Incorporating 20 to 30% compost (by volume) into soils of various
texture and quality is often an appropriate application rate. The
following generic directions are suggested if upfront soil analyses
are not completed.
Application recommendations
In-situ
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Cultivate the soil, to a depth of 300mm when ground conditions
are reasonably dry.
Uniformly apply a 25 to 50mm layer of compost.
Incorporate the compost to a depth of 100 to 200mm.
Smooth the treated area, and remove any stones or debris from
the surface prior to planting.
Ex-situ
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Check that site drainage conditions have been rectified.
Place soil, sand and/or aggregate piles near the compost pile.
Determine compost inclusion rate and convert it into a blending
ratio.
With this ratio in mind, create a bed of compost (usually the
lightest material), then apply the appropriate number of scoops
of mineral materials evenly on top (heavier materials). Do the
blending on concrete if possible.
Using a front-end loader, scoop up the layered material from
underneath, and dump it forward – to the front or past the soil
bed. Try to ‘feather out’ the material from the front-end loader
bucket when dumping so that it blends as it falls.
Working through the middle of the soil bed, incorporate
materials from either side. This should eventually displace the
soil bed, moving it forward, as the blending continues.
Continue until the materials are adequately mixed.
The manufactured topsoil should be spread a minimum of
150mm deep for turf and 300 to 600mm deep for tree/shrub
planting areas.
Compost can often supply the nutrients needed for the first 6
to 12 months after planting. Turf and food gardens are likely to
require additional fertilization.
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PO Box 31580 North Shore City 0741 Auckland . tel 09 4866722 . www.wasteminz.org.nz