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The New Zealand Institute for Plant & Food Research Limited
Rootzone reality – a fluxmeter network to
measure and manage N leaching losses
on cropping farms
PAANZ Workshop – Technology to reduce N leaching
Paul Johnstone, Plant & Food Research
The New Zealand Institute for Plant & Food Research Limited
A rapidly changing farming landscape
» Goal of farmers hasn’t changed – Farming for profit while
minimising losses
» Period of regulatory change – intent vs demonstrate
» Rise of tools for predicting whole farm outcomes and setting
associated policies
» Model vs measure
» Recognition that farming systems are complex!
The New Zealand Institute for Plant & Food Research Limited
Plugging a gap – ‘Rootzone reality’
» Provide growers and regional authorities with robust
measurements of N and P leaching losses from cropping
farms across sites and seasons under GMP’s
» Why?
» Need more measured data for discussion
» Need an idea about whether GMP’s have the desired impact
» Need to do it together to inform models and policy
Overview:
» Summary of network and sites
» Year 1 findings
» The role for precision technologies?
The New Zealand Institute for Plant & Food Research Limited
Measuring losses - tension fluxmeters
» Why use tension fluxmeters?
» Permanent and non-intrusive
» Capture complete drainage events
» Cost-effective approach
» What is a tension fluxmeter?
» PVC pipe that intercepts drainage (stores ~14 L)
» Silica sand and DE reduce sediment transfer
» Passive wick
» Drainage pumped to surface through plastic tubes
150 mm
50 mm
1000 mm
200 mm
150 mm
The New Zealand Institute for Plant & Food Research Limited
Context - installing and testing fluxmeters
» Installation process
» Representative areas of fields, not extremes
» Hole augured, unit lowered, soil carefully
repacked
» Top of fluxmeter is at a depth of 1.0 m
» Testing performance
» Disturbed soil needs to settle
» Soil water balances to look at inputs (irrigation
+ rainfall) and outputs (drainage)
The New Zealand Institute for Plant & Food Research Limited
The fluxmeter network
» Network design
» Four monitor regions
» Three sites per region
» 12 fluxmeters per site (144 units)
» Sites
» Commercial fields
» Range of soils, climates and
management practices
» Avoided high water tables,
artificial drainage and stones
The New Zealand Institute for Plant & Food Research Limited
Key measurements
Soil fertility (N, P, C…)
Crop biomass (DM, N uptake, export)
Drainage (volume, NO3, NH4, DRP, Total P)
The New Zealand Institute for Plant & Food Research Limited
Drivers of nutrient losses – loading and drainage
Implication: manage soil fertility and drainage
Low drainage High drainage
Low soil fertility Low loss Low loss
High soil fertility High risk High loss
The New Zealand Institute for Plant & Food Research Limited
1 2 3 4 5 6 7 8 9 10 11 12
0
100
200
300
400
1 2 3 4 5 6 7 8 9 10 11 12
0
100
200
300
400
Measured loading – soil nitrogen
High
Moderate
Min
era
l N
(kg
/ha,
to 1
m d
ep
th)
AM
N
(kg
/ha,
to 1
m d
ep
th)
High
Moderate
Low
Low
Canterbury Manawatu Hawke’s Bay Waikato/Auckland
N available today…
N available soon…
The New Zealand Institute for Plant & Food Research Limited
1 2 3 4 5 6 7 8 9 10 11 12
0
50
100
150
200
250
Measured loading – soil phosphorus
Optimum
Ols
en
P
(mg
/kg
, to
0.2
m d
ep
th)
Canterbury Manawatu Hawke’s Bay Waikato/Auckland
Above
optimum
The New Zealand Institute for Plant & Food Research Limited
1 2 3 4 5 6 7 8 9 10 11 12
0
250
500
750
1000
1250
15000
500
1000
1500
2000
2500
3000
Drainage
Rainfall
Irrigation
Long term average rainfall
13 12 12 11 12 5 13 12 13 5 7 6
NR
NR No result
13 12 12 11 12 5 13 12 13 5 7 6
Measured drainage
Rain
fall
and irr
igation (
mm
)
Canterbury Manawatu Hawke’s Bay Waikato/Auckland
Dra
inage (m
m)
Monitoring period (months)
The New Zealand Institute for Plant & Food Research Limited
Measured nitrogen lossesC
um
ula
tive m
inera
l N
losses (
kg/h
a)
Canterbury Manawatu Hawke’s Bay Waikato/Auckland
What represents an acceptable
environmental loss?
What represents an acceptable
economic loss?
The New Zealand Institute for Plant & Food Research Limited
Measured phosphorus lossesC
um
ula
tive T
ota
l P
losses (
kg/h
a)
What represents an acceptable
environmental loss?
Not an economic driver
Canterbury Manawatu Hawke’s Bay Waikato/Auckland
The New Zealand Institute for Plant & Food Research Limited
Overall synthesis from network to date
» Key stats since installation and October
» Captured drainage ranged from 0.3 to 611 mm
» N losses ranged from 0.2 to 226 kg N/ha
» P losses ranged from 0.01 to 0.56 kg P/ha
» Winter and spring losses dominate
» Rainfall is a key driver; reduce loading?
» Irrigation not resulting in significant drainage during summer
» High soil N and P levels = high risk
» Value of data increases with long-term trends…
The New Zealand Institute for Plant & Food Research Limited
Implications for precision technologies?
» Tight management of water and nutrients
is important to limit losses
» GMP’s are working
» Precision technologies can also help
» Likely to require different solutions
» mapping, sensing, VRI, VRN…
» How to decide what to use and when?
The New Zealand Institute for Plant & Food Research Limited
Acknowledgements
Grower collaborators
Project managers: Diana Mathers (FAR) and Angela Halliday (Horticulture NZ)
PFR team: Matt Norris, Shane Maley, Mike George, Gina Clemens, Steve Thomas, Steve
Green, Carlo van den Dijssel, Paulo Zuccarini, Nathan Arnold, Adrian Hunt, Christina
Finlayson, Glen Clark and Peter Wright.