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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.
The New Zealand Institute for Plant & Food Research Limited
Paul.Johnstone@plantandfood.co.nz
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