2.5. Carbon fractionation
Soil samples, used to determine the different types of soil carbon,
were obtained by aggregating a fixed mass of soil from each sampling
point within a treatment for the 0–10 cm and 10–20 cm depth increments.
Five samples from each aggregated treatment and depth pool
were then separated into fractions using the Zimmermann et al.
(2007) method. The five fractions derived were dissolvable organic carbon
(DOC), particulate organic matter (POM), chemically resistant soil
organic carbon (rSOC), sand and stable aggregates (S + A), and silt
and clay fraction (s + c). The chemically resistant soil organic carbon
(s + c-rSOC) is derived from the value of s + c minus rSOC.
2.6. Fine root mass
Fine root mass density (FRMD) was measured by releasing fine roots
from the soil cores used to determine bulk density. To release the fine
roots, the core was inserted into a 250 cm3 plastic bottle, filled with
deionised water and placed inside an end-over-end agitator for at
least 12 h. The root material was then floated off from the bottle, and
caught on a sieve with 710 μm apertures. The clay and silt slurry was
washed away, and root material dried at 105 °C and then weighed.
The fine root mass density (mg cm−3
) was calculated as the mass of
the fine roots divided by the core volume.
2.7. Soil moisture content
Soil moisture was measured at three points in each of the three
treatments (nine access tubes; Fig. 1) on a fortnightly basis between
23 October 2013 and 19 March 2014 using a ‘Diviner 2000’ capacitance
probe (Sentek Sensor Technologies, 77 Magill Road, Stepney SA 5069,
Australia. www.sentek.com.au). Readings were taken at 10 cm
increments between 15 cm and 125 cm, however one tube in both the
woodland and silvopastoral treatments (Fig. 1) extended to a reduced
depth, due to difficulties in installing the tubes by hand. Volumetric
moisture content (θv) was calculated using the calibration equation
for a nearby clay soil given by Burgess et al. (2006).