Soil carbon, nitrogen use efficiency and the CFI
in the cane farming system
Phil Moody, Weijin Wang, Ram Dalal
Soil Processes
Department of Science, Information Technology, Innovation and the Arts
What the CFI means for the sugar industry
CFI aims to reduce/mitigate emissions of the greenhouse
gases- carbon dioxide, nitrous oxide, methane
Focus for cane farming:
Carbon dioxide (CO2) – can carbon be sequestered in the
soil via plant biomass production?
Nitrous oxide (N2O) – can emissions be reduced?
(agriculture contributes 86% of national N2O emissions)
Department of Science, Information Technology, Innovation and the Arts
Soil carbon – what is it?
• Soil carbon occurs as inorganic (carbonates in
alkaline soils) and organic forms
• Focus of CFI is soil organic carbon
Department of Science, Information Technology, Innovation and the Arts
Soil organic carbon- what is it?
Living roots
Charcoal
Soil fauna
Plant residues
Microbes
Department of Science, Information Technology, Innovation and the Arts
Humus
Soil carbon – how is it classified?
Department of Science, Information Technology, Innovation and the Arts
Soil organic carbon- how is it classified?
Department of Science, Information Technology, Innovation and the Arts
Soil organic carbon- why is it important?
Apart from impacting on greenhouse gases, soil organic
carbon is the main driver of ‘Soil health’
Soil health: comprises key chemical, physical, biological
components
Chemical
- nutrient holding capacity
- resistance to acidification (pH buffer capacity)
Physical
- aggregation (structure)
- water holding capacity
Biological
- nutrient mineralisation (particularly nitrogen)
- disease suppressiveness
Department of Science, Information Technology, Innovation and the Arts
Has my soil got adequate organic carbon to be
healthy?
• ‘Ideal’ level depends on climate, soil type, and
cropping system- there is not one ‘critical’ value.
• ‘Ideal’ level supports suitable chemical, physical and
biological conditions for a sustainable, profitable
system.
Department of Science, Information Technology, Innovation and the Arts
How does your soil measure up?
Visit www.soilquality.org.au
Department of Science, Information Technology, Innovation and the Arts
Increasing soil carbon levels: Land use change options
Department of Science, Information Technology, Innovation and the Arts
Increasing soil carbon levels: Land use change options
•
•
•
•
Cropping
ley (pasture)
Cropping
permanent pasture
Cropping/pasture
afforestation
Plantations
reforestation
Department of Science, Information Technology, Innovation and the Arts
Increasing soil carbon levels: Cane farming system
options- green cane vs burnt cane? Till vs no-till?
No significant effect of trash versus burnt system
or till no-till on soil C to 30 cm
Difference in organic carbon stocks for 0-0.3 m at the Bundaberg trash/ tillage trial site
for conventional tillage (CT) and no-till (NT) treatments.
Vertical bars are standard deviations.
Page, K.L., Bell, M., Dalal, R.C. Soil Research (in press)
Department of Science, Information Technology, Innovation and the Arts
Increasing soil carbon levels: Cane farming system
Take home messages:
• manage soil organic carbon for soil health benefits
• any increase in soil carbon stocks (sequestration) will be
a bonus!
Department of Science, Information Technology, Innovation and the Arts
Climate Change Research Program: Soil carbon
2012-2015
National Soil Carbon Program
Main Objectives:
• Filling the Research Gaps (Increasing soil carbon)
• Improved measurements (in situ VIS-NIR, NIR-MIR, temporal change)
• Crop, pasture management (N inputs, perennial pastures, grazing, C
inputs)
• Vegetation management (regrowth, plantation forestry, reforestation)
• Amendments (compost, biochar)
• Modelling (measurement and modelling linked to reduce costs)
• Linking to CFI methodology (e.g., managed forest regrowth)
• Linking to Action on the Ground projects
Department of Science, Information Technology, Innovation and the Arts
Nitrous oxide – what is it?
• Nitrous oxide (N2O) is 298 times more potent as a greenhouse
gas than carbon dioxide.
• Reducing nitrous oxide gas emissions is a focus area of CFI.
• In the cane farming system the main emissions of N2O occur
following N fertiliser application or where nitrate-N has
accumulated in the soil following short
term horti crops or legume break crops.
Department of Science, Information Technology, Innovation and the Arts
How is nitrous oxide measured?
Measure on site or take gas sample back to lab and analyse.
Automatic systems measure throughout day but limited spatially.
Department of Science, Information Technology, Innovation and the Arts
What processes cause nitrous oxide emissions from
soils?
Denitrification is the major cause of N2O emissions
nitrate
nitrite
NO3-
NO2-
NO
N2O
N2
Denitrification is dependent on simultaneous occurrences of:
• nitrate
• anaerobic soil conditions (i.e., saturated soil ..well sort of!)
• dissolved organic C (e.g., trash blanket is a 5* source)
• temperature
Department of Science, Information Technology, Innovation and the Arts
Measuring nitrous oxide gas emissions
Manual/ auto gas chamber
NO3-
NO2-
NO
N2O
N2
….but the proportion of nitrogen gas/nitrous oxides varies from
1% to 99%!
(depends on: temperature, soil pH, soil water content, nitrate concentration and
dissolved organic carbon)
In the cane farming system, denitrification can cause
large N losses- every kg N lost costs you money!
Department of Science, Information Technology, Innovation and the Arts
30
0
(a)
25
50
20
15
10
100
Soybean
sowing
Cane
Tillage planting
Cane
harvest
Fertilisation
Daily rainfall (mm)
Mineral N (kg/ha) / temperature (oC)
Is nitrogen loss by denitrification important in the
cane farming system?
Soybean fallow nitrate
150 N urea nitrate
150
5
0
600
400
Daily N2O fluxes (g N/ha/d)
(b)
Daily rainfall (mm)
Daily mean temperature
BF-S+0N
SF-S+0N
BF-S+150N
BF-S+150N+DMPP
SF-S+75N
800
Auto chambers
200
0
800
(c)
Manual chambers
600
400
Soybean fallow N2O
150 N urea N2O
Nitrous oxide emissions
10 kg N/ha/yr lost from soybean fallow
6-9 kg N/ha/yr lost from 150 N urea
….but this is only a fraction
of the N lost by denitrification
200
0
01 Jan
2010
01 Mar
2010
01 May
2010
01 Jul
2010
01 Sep
2010
01 Nov
2010
01 Jan
2011
01 Mar
2011
01 May
2011
01 Jul
2011
Wang et al. (2010) ASSCT Conf.
Department of Science, Information Technology, Innovation and the Arts
Time (d/m/y)
N loss pathways in the cane farming system
Volatilisation
Denitrification
Legumes
Surface
Runoff
Mud &
Dunder
Trash
Urea
Water logging
Mineralisation
Soil
Organic
Matter
Ammonium
NH4
Nitrate
NO3
Nitrite
NO2
- N loss pathways
- N movement in soil
Leaching
Reducing nitrous oxide emissions: Cane farming system
Take home messages:
• maximise N recovery by the crop
(fertilise for realistic block yield targets; split applications;
legume break crop residue management)
• keep nitrogen in the ammonium form
(nitrification inhibitors; slow release urea)
• any N loss is costing you money!
Department of Science, Information Technology, Innovation and the Arts
Climate Change Research Program: Nitrous oxide
2012-2015
Nitrous Oxide Research Program II
Main Objectives:
• Optimising nitrogen fertiliser applications, timing, placement
• Increasing nitrogen use efficiency
• Slow-release fertiliser (polymer-coated urea)
• Alternative N sources (legume nitrogen – reduce transportation GHG)
• Additives: urease and nitrification inhibitors (Green Urea, ENTEC)
• Modelling
• Developing linkages to CFI methodology (nitrogen management, especially
on nitrogen fertiliser use)
Department of Science, Information Technology, Innovation and the Arts
Thank you
• For more information about ongoing projects
[email protected] (soil carbon)
[email protected] (nitrous oxide)
[email protected] (nitrous oxide)
[email protected] (N fertiliser use efficiency)
Department of Science, Information Technology, Innovation and the Arts
How is soil organic carbon measured?
Sample collection
• Randomly locate 25 m x 25 m square
• Divide into 5m x 5 m grid
• Randomly select 10 points for sampling
(random distribution between row/interrow
positions)
• At each point take 0-10 cm, 10-20 cm,
20-30 cm samples with corer of
min. i.d. 40 mm
• Bulk samples by depth
• Require 3 samples for bulk density for
each depth
Department of Science, Information Technology, Innovation and the Arts
How is soil organic carbon measured?
Sample analysis
• sample dried @ 40C
• sample crushed < 2 mm
• subsample ground <5 um
• subsample acid tested for carbonate.
If present, subsample treated with
sulfurous acid.
• total organic carbon determined by
Dumas dry combustion on carbon
analyzer.
Department of Science, Information Technology, Innovation and the Arts
How is soil organic carbon measured?
Carbon fractionation
Particulate organic C (> 50 um)
- generally more sensitive to land management than total organic C
- residence time: months to years
Humic C (< 50 um)
- generally largest proportion of total organic C
- residence time: years to decades
Resistant organic C
- fraction associated with C sequestration
- residence time: decades to centuries
Particulate organic C
• treat < 2mm sample with sodium hexametaphosphate
• wet sieve through 50 um sieve
• soil retained on sieve is dried and weighed
• ground < 5 um and analysed for total organic carbon as before
Department of Science, Information Technology, Innovation and the Arts
Near-infrared and Mid-infrared spectroscopy
reduces cost of carbon measurement
“MIR continues to look promising as a
rapid cost effective means of analysing
total soil carbon – applicability to fractions
remains to be tested”
“Field-based NIR has the potential to rapidly
measure soil carbon once the unit has been
rigorously calibrated against standard
techniques”
Department of Science, Information Technology, Innovation and the Arts