Can different pasture management
methods increase soil carbon?
Garth Coghlan1, Kerry Bridle1, Mark Hovenden2
1 Tasmanian Institute of Agriculture, University of Tasmania, TAS, Australia,
Email [email protected]
2 School of Plant Science, University of Tasmania, TAS, Australia
Introduction
Strategies being trialled
Semi-native dryland pastures in Tasmania have been severely impacted by
inappropriate grazing regimes and drought. Various grazing and pasture
management strategies have been trialled in an attempt to reduce soil
erosion and increase agricultural productivity.
Sown perennial pasture
This study investigates trials on 20 Tasmanian farms (Fig. 1). These
strategies vary in their cost of implementation and their effect on
productivity
d ti it (Fig.
(Fi 2).
2) In
I collaboration
ll b ti with
ith our project
j t partners,
t
we ask
k the
th
question ‘How effective are these strategies at increasing soil
carbon?’.
New varieties of perennial pasture
species have been developed that
are persistent over long time
periods,
including
drought.
Providing year round ground cover
reduces soil erosion, increases
productivity and may increase soil
carbon. Trial sites range in age from
2 to 25 years.
Sown perennial pasture on a north-facing
slope Photo: Eric Hall
Use of amendments
Figure 1:
Distribution of trial
sites across
Tasmania.
Farmers are trialling a range of amendments to increase site productivity:
•
increasing soil organic matter (via compost and poppy waste)
•
improving saline soils with gypsum or acidic soils with lime
•
supporting
g soil biology
gy ((use of compost teas).
)
These young (< 3 year old) trials have been supported by NRM North and
NRM South.
Blue: grazing method
green: sown
perennial pasture
light blue:
amendments
pink: native
restoration
white: long-term
long term
exclusion
Changing grazing
management
Conventional
grazing
Rotational
grazing
In recent years some farmers have
moved from set-stocking to rotational
grazing with assistance from NRM
y
North and NRM South. In this study,
sites have been rotationally grazed
for less than four years (postdrought).
Stock exclusion
Methods
It is difficult to detect change in soil carbon stores under different grazing
practices, particularly in the short-term (<5 years) (Sanjari et al. 2008,
Ch
Chan
et al.
l 2010).
2010) Paired
P i d sites
i
h
have
b
been
carefully
f ll chosen,
h
and
d labile
l bil
carbon measured to provide an indicator of short-term response to
management.
A minimum of three farms were selected to investigate each strategy. At
each site, a “cross-fence” comparison was made between the treatment
and traditional management. Twelve soil cores (4 groups of 3, 30 cm deep)
were taken as paired samples either side of a fence line, pasture
assessments conducted and growth rate measured with pasture cages.
Soils will be analysed for basic nutrients, total and particulate carbon.
Sown perennial pasture
Effect on agricultural
production
+
Changing grazing management
North-facing slopes are particularly sensitive to over-grazing, resulting in
loss of groundcover and soil erosion. Since 1999, over 300 north-facing
slopes have been fenced off to exclude livestock and allow recovery.
North-facing slope
N ti restoration
Native
t
ti
Greening Australia has three on-farm trials to investigate the role that
biodiverse carbon plantings can play in increasing biodiversity and carbon
storage in degraded landscapes. Baseline soil carbon measurements from
2010 will be compared to samples taken in 2013.
Pasture amendments
Cost of implementation
Long-term exclusion
-
Native restoration
Discussion
This project will finish in June 2014 and will:
•
Collect baseline data on soil carbon stocks for future reference
•
Add to our scientific knowledge about the comparative value of onfarm strategies for increasing soil carbon, and
•
Provide farmers with more information on the relative usefulness of
different methods of soil carbon sequestration.
Figure 2: The relative cost of implementation of the different management
strategies and their effect on agricultural production.
References
Acknowledgements
This project is supported by funding from the Australian Government Department of Agriculture, Fisheries and Forestry as part of its
Carbon Farming Futures – Action on the Ground program.
CHAN, K. Y., OATES, A., LI, G. D., CONYERS, M. K., PRANGNELL, R. J., POILE, G., LIU, D. L. & BARCHIA, I. M. 2010. Soil carbon
stocks under different pastures and pasture management in the higher rainfall areas of south-eastern Australia. Soil Research, 48, 715.
Thanks to our project partners NRM South, NRM North, Greening Australia and Serve-Ag, to our participating farmers, the project
advisory committee and to Mark Downie.
SANJARI, G., GHADIRI, H., CIESIOLKA, C. A. A. & YU, B. 2008. Comparing the effects of continuous and time-controlled grazing
systems on soil characteristics in Southeast Queensland. Soil Research, 46, 348-358
Photo: Tanya Bailey Rotational grazing Conventional grazing