This presentation was presented during the 2 Parallel session on Theme 3.2, Managing SOC in: Grasslands and livestock production systems, of the Global Symposium on Soil Organic Carbon that took place in Rome 21-23 March 2017. The presentation was made by Mr. David Whitehead, from University of Waikato – New Zealand, in FAO Hq, Rome

1. Soil organic carbon stock
changes under grazed
grasslands in New Zealand
Louis Schipper, Paul Mudge, Miko Kirschbaum,
Carolyn Hedley, Nancy Golubiewski,
Simeon Smaill, Francis Kelliher,
David Whitehead

2. Historical increase in establishment of grasslands
800 years ago
Pre-human
Post European
settlement
Pre European settlement
Post Māori burning
Mostly year round outdoor grazing Landcare Research
Land area
268,021 km²

3. New Zealand
• Rapid conversion to intensive dairy farming over 2 decades
• 20.9 billion litres milk/year – 3% of global total
• 49% of greenhouse gas emissions derived from agriculture
• What are the impacts on soil carbon in grazed grasslands?
• Can we increase soil carbon to offset agricultural emissions?

4. Landuse
Pre-1990
natural forests
Pre-1990
planted
forests
Post-1989
planted
forests
G
rassland
with
woodybiom
ass
High-producing
grassland
Perennial cropland
Annual cropland
Vegetated
wetland
Change
in soil carbon
(Mg C ha-1)
-50
-40
-30
-20
-10
0
10
20
30
Average grassland carbon stock (0-0.3m depth) = 106 Mg C ha-1
Long-term changes in soil carbon when converted to low-producing grassland
McNeill et al (2014), Tate et al (2005), Schipper et al (2017)
Mean +/- SE

5. Change in carbon stocks for grasslands
Resampling sites to 1 m depth after
sampling 20-40 years previously
Analysis using archived soil samples
Schipper et al (2014)
Photo: Alice Barnett

6. Flat land
Schipper et al (2014)
-10 Mg ha-1
-15 Mg ha-1
5 Mg ha-1
Change in carbon stocks for grasslands over 20-40 years

7. Hamilton
Rukuhia Moanatuatua
Hauraki
• About 1% of NZ land surface
• Productive land when drained
• Often 10+ m deep
• Carbon loss of -2.9 Mg C ha-1 y-1
• Date available for only one site
Komakarau
Figure adapted from: www.landcareresearch.co.nz/science/plants-animals-
fungi/ecosystems/wetland-ecosystems
Campbell et al (2015), Nieveen et al (2005)
Organic soils: a special case

8. Note: Recovering topsoil, shallow sampling
Schipper et al (2013), Condron et al (2012)
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
3
4
5
Carbon%
1960 1970 1980 1990 2000
Year
WnoP
WresP
WhiP
Management effects: addition of phosphorus fertiliser
62 years of observations at Winchmore with border dyke irrigation
No P addition
Intermittent P addition
High P addition
Phosphorus fertiliser
• doubled forage
production
• no change in soil
carbon

9. Sampling of adjacent irrigated and non-irrigated sites
7 Mg C ha-1 loss for sites irrigated 3-90 years at depth 0-0.3 m
Mudge et al (2017)
Management effects – irrigation
Irrigation duration (years)
0 10 20 30 4080 90
Irrigated-unirrigatedsoilcarbonstocks
(MgC/ha,depth0-0.3m)
-30
-20
-10
0
10
Box plot
Short-term estimates of carbon balance at Beacon Farm
Winchmore border dyke irrigation
Depth 0-1 m, difference between 20% irrigated and dryland

10. • soil carbon in A horizon
8.6 ± 4.1 Mg C ha-1 less in dairy
compared with dry stock
• difference of 9.6 ± 7.9 Mg C ha-1 at
0-0.6 m depth but not significant
• mainly Allophanic soils
Barnett et al (2014), Houlbrooke et al (2008)
Management effects – animal stock

11. Rutledge et al (2017a)
Management effects –grassland renewal
Soil water content (%)
Soilcarbonloss(gCm-2d-1)
Soil carbon loss -0.8 to -4.1 Mg C ha-1
regulated mainly by:
• soil water content status
• length of time the soil surface is
left exposed
No decrease of rates of carbon loss
before seedlings emerge
Daily carbon loss for no till is the
same as that for full cultivation

12. Net ecosystem carbon balance for
• ryegrass/clover
• mixed species sward
Rutledge et al (2017b)
Management effects –grassland composition
Net carbon uptake years 2 to 4 Dry matter production Mg/3 years
relative to year 1 (g C m-2)
Ryegrass
control
Re-grass
with
mixed
sward
Re-grass
with
ryegrass
Change to mixed sward compared with replacing ryegrass
• retains more soil carbon
• increases forage production

13. Summary
Historical changes in soil carbon
Flat land
• carbon losses from Allophanic and
Gley soils over 30 years
• large ongoing carbon losses from
Organic soils (1 site)
• no change for other soil orders
Hill country
• long term increases
Chris Morcom
Management effects on soil carbon
• phosphorus addition – no detectable
change
• nitrogen addition – no data
• irrigation – lower at irrigated sites
• animal stock – small effect?
• grassland renewal – small loss but may
recover if infrequent
• mixed swards may maintain carbon stocks
and increase production
Schipper et al (2017) A review of soil carbon change in New Zealand’s grazed grasslands.
New Zealand Journal of Agricultural Research doi: 10.1080/00288233.2017.1284134
Request more information from Louis Schipper louis.schipper@waikato.ac.nz