AOTGR1-42
Protocol for ‘Paired Paddocks’ in the DAFF project:
‘Farmers leading and learning about the soil carbon frontier’
The theory behind ‘paired paddocks’ as an extension tool, is to effectively communicate and
demonstrate how management practices can impact on soil organic matter. A ‘paired paddock’
demonstration consists of comparing two paddocks, with the same, or at least similar soil type, but with
different management histories. During discussions on what soil organic matter is, what its functions
are, what it consists of, and what the benefits of soil organic matter are, it is also very important to
show farmers how to sample for soil Carbon following SCaRP guidelines.
Background information for ‘Paired Paddocks’


Select two paddocks (often on adjoining farms) with similar soil types but with different histories
(eg. pasture vs. cropping, or NoTill vs. cultivation, or long term NoTill vs. short term NoTill, or with
sheep vs. without sheep etc.)
See attached as an example of a paired paddock comparison
Paddock History:
For each paddock collect 5 years of historical information (eg. 2008 to 2012):
(i)
Crop type, fallow or pasture (include crop yield)
(ii)
Grazing pressure (light, moderate or heavy)
(iii)
Tillage (how often per year)
(iv)
Crop establishment: NoTill, Traditional cultivated seed bed etc
(v)
N fertiliser use
(vi)
Take a photo of the paddock when soil sampling
In the paddock: sampling for (i) soil Carbon and (ii) Bulk Density
Sampling for Soil C is relatively straight forward. Unfortunately without Bulk Density (BD) it is not
possible to calculate the quantity (kg/ha) of Soil C in a paddock. We have to determine both Soil C and
BD for a minimum of ten sampling sites per paddock so that the variability within the paddock can be
determined - this is important if the paddock is sampled again in the future because without a measure
of variability you cannot accurately compare Soil C levels over time.
What you need:
 GPS
 For Soil C: A soil tube (around 40mm diam) and the means to push/hit it accurately into the ground
 For Soil BD: the proper set up for measuring BD using undisturbed rings (see note on BD below)
 Tape measure
 Duct tape to mark 10 and 30 cm on the soil tube
 Ruler
 Spade
 Soil bags either sealed plastic or strong paper bags clearly marked with the date, owners name,
paddock name, sample site number, sampling depth and BD or SC.
1
NOTE on Bulk Density sampling: We prefer using the undisturbed ring technique for bulk density
sampling, but appreciate that most groups may not have access to this equipment nor had the training
on how to use it. An excellent reference to Bulk Density sampling can be found in ‘Soil Matters, by
Neale Dalgliesh and Mike Foale 1998, published by APSRU. You can download the whole book or
sections from the web: www.apsim.info/Wiki/public/Upload/ApSoil/SoilMatters
You will find the information on sampling for Bulk Density in Section 4 (Determining plant available
water capacity).
Just briefly, there are two techniques:
(i) using undisturbed rings which is the most accurate but also the most labour intensive (and you need
the equipment); and
(ii) using a normal tube used for soil sampling. NOTE of warning: one reason why this technique tends
to be less accurate is that you need to use a large diameter tube, anything less than a 75mm diameter
tube is not good enough (see Soil Matters, p 77).
Step wise:
1. Determine with the owner of the paddock the main soil types in the paddock. Draw a mud map of
the main soil types in the paddock. Make sure you include some easily identifiable features in the
paddock (locate north, road, gate, dam, trees etc).
2.
Sample the same soil type in each ‘paired paddock’.
3.
On the selected soil type sample for Soil Carbon at 10 randomly distributed sampling sites at two
depths (0-10 and 10-30cm), locate rough position of each site on your mud map and record each
site with a GPS lat/long, numbering them 1 to 10.
4.
At each of the 10 sampling sites for Soil Carbon you will also have to collect Bulk Density samples for
both the topsoil (0-10cm) and subsoil (10-30cm). You will need to take 10 BD topsoil samples
regardless if you are using the ‘tube’ or ‘ring’ technique (there is high variability in BD across the
paddock in the topsoil). For subsoil BD sampling we take 5 samples (every second sampling site)
when using the rings; and 10 if using a soil tube (because of the decreased accuracy).
5.
On the soil tube, accurately measure and mark with duct tape, 10 cm and 30 cm from the base of
the tube. Measure and record the diameter of the soil tube with callipers (mm).
6.
NOTE: Do NOT Use CRC, WD40 or Canola Oil LUBRICANTS. THESE ALL CONTAIN CARBON! If a
lubricant is required use only a Silicone based product.
7.
Always sample between the crop rows. If the paddock is in pasture, sample randomly or if you can
see old crop rows sample between the rows.
8.
When you have selected a sampling site, cut any vegetation to ground level and remove. Carefully
scrape off any loose vegetative material from the sampling site.
2
9.
SOIL CARBON 0-10. On the cleared area push or hit the tube into the topsoil so that the 10 cm mark
is level with the soil surface, remove the tube and collect the 0-10cm soil for the Soil Carbon
measurement and put into a labelled bag. You may have to take more than one sample to ensure
at least 200g is collected.
10. SOIL CARBON 10-30. Using a spade, carefully dig away the topsoil to 10 cm (measure this
accurately!) so that none of the topsoil can fall into the hole for the 10-30 sample. Push (with a soil
sampling rig) or hit (with a sledgehammer) the tube into the ground until the 30 cm mark is level
with the surface of the 10cm deep platform. Remove the tube and collect the 10-30cm sample into
a labelled bag.
11. Move to an undisturbed sample area next to the last hole and cut any vegetation to ground level
and remove. Carefully scrape off any loose vegetative material from the sampling site.
12. Bulk Density 0-10.
(i) Ring technique: drive the ring assembly into the soil till you have reached the exact depth of the
ring (making sure you don’t compress the sample!). Carefully extract the ring assembly to ensure
no soil is lost from the bottom of the ring. Clean soil flat with the top and bottom of the ring and
empty the ring into a marked sealed plastic or paper bag for drying and weighing.
(ii) Tube technique: push or drive the tube into the soil to exactly 10 cm level with the soil surface.
Gently remove the tube without losing any soil from the base of the tube. Put all of the soil into a
marked sealed plastic or paper bag for drying and weighing. Measure the exact depth of the hole
with a measuring tape, to the nearest mm, and record on the bag if it is not exactly 10cm.
13. Bulk Density 10-30.
(i) Ring technique: With a spade dig away the soil to about 15cm depth and make a small working
platform so that topsoil cannot fall into the subsoil sample. Drive the ring assembly into the soil till
you have reached the exact depth of the ring (making sure you don’t compress the sample!).
Carefully extract the ring assembly to ensure no soil is lost from the bottom of the ring. Clean soil
flat with the top and bottom of the ring and empty the ring into a marked sealed plastic or paper
bag for drying and weighing.
(ii) Tube technique: Using a spade dig away the soil to 10 cm (measure with ruler) and make a small
working platform so that none of the topsoil can fall into the 10-30 sample. Drive the tube into
ground to the 20cm mark where it is exactly level with the soil surface of the platform at 10cm
depth. Gently remove the tube making sure you don’t lose any soil from the base of tube. Put the
10-30 cm sample into a marked and sealed plastic or paper bag for drying and weighing. Measure
the exact depth of the hole you have made with a measuring tape, to the nearest mm, and record
on the bag.
If you loose soil from the tube or bag you will need to repeat the sample.
14. Repeat for each of the 10 sites.
3
In the Laboratory
Soil C analysis
1. Dry the samples for Soil Carbon analysis at 40oC in a force draught oven for 48 hours. After drying,
store samples in labelled bags until they are dispatched to the laboratory.
Bulk Density samples
1. Prepare a lab sheet and record:
> paddock name
> sample number and depth
> aluminium tray number (if the samples are in strong paper bags they can stay in the bag)
> tray or paper bag weight (in grams, to one decimal place)
> wet weight (in grams, to one decimal place) of the soil (soil + tray)
2.
Place in a force draught oven at 105oC for 72 hours. Take out of the oven and record dry weight
(soil + tray). (A wet heavy clay may take longer than 72 hours to dry).
3.
If there is gravel, buckshot or rocks in the sample you will need to sieve the sample to pass through
a 2mm sieve. Separately weigh the gravel or rocks remaining on top of the sieve, record weight.
4.
Determine the diameter of the ring or tube you used in the paddock. With callipers measure the
inside diameter of the tube.
Use the accompanying spreadsheet to calculate the bulk density (Bulk density calculator.xlsx).
Note the calculation is (as a guide BD should be between 0.9 and 1.8 g/cm3):
BD = (Weight of Dry Soil – Tray or bag weight – Gravel weight)
(Volume of soil core – Gravel weight / 2.65)
Calculation of Soil C content in the paddock
5.
When you get the Soil C results from the lab (and its fractions) you can calculate the amount of soil
Carbon in the paddock using:
http://soilquality.org.au/calculators/gravel_bulk_density
It is an easy to use web site and the calculations are straight forward.
Harm van Rees
31/08/2012
4
A few photos with handy hints
Clear stubble and fine material away
to make a clean working surface soil
Hammer tube into the ground
(for the deep samples we used a
sledge hammer)
Have a ruler level to the ground so
you can easily see the depth you
need to sample to
BD ring assembly
BD sampling topsoil
BD sampling subsoil
5
Check depth with a tape
measure (up against the ruler),
record if it is not exactly 30cm
Check to make sure there is a
clear break of soil at the
bottom of the tube (twist the
tube before pulling it out)
Working example only
Farmers leading and learning about the soil carbon frontier
Paired paddock comparison
for soil carbon
Normanville Group
August 2012
Mallee alkaline clay loam,
gentle slope towards the southwest
Contrast in Land-use:
Main issues:
Year:
Paddock history:
Yield (t/ha):
N inputs (kg N/ha):
Grazing:
Total Soil Carbon %
Total Nitrogen %
C:N ratio
Bulk density g/cm3
Particulate Carbon kg/ha
Humus kg/ha
Charcoal kg/ha
Bremner
Hunt p17
35.52.10oS, 143.41.19oE
35.52.09oS, 143.41.26oE
No Till stubble retained
Traditional cultivated crop establishment
 Does long term NoTill stubble retained systems have higher soil Carbon levels compared to traditional crop establishment practices?
 Are there differences in humus content (stable Soil C fraction) between the two management systems?
 How can you raise soil Carbon levels in cropping soils?
2008
2009
2010
2011
2012
2008
2009
2010
2011
2012
Canola
Wheat
Wheat
Barley
Canola
0.1
1.3
3.8
4.2
xx
2.5
9.1
2.4
34.4
43.1
Light grazing on agistment over summer
Topsoil (0-10cm): 1.29
Subsoil (10-30cm): 1.42
Nitrous Oxide emissions
kg/ha CO2e (2008 to 2012) from
N fertiliser
6
Topsoil (0-10cm):
Subsoil (10-30cm):