rootzone reality a fluxmeter network to measure and … · rootzone reality –a fluxmeter network...

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


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!


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?


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


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 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


Key measurements

Soil fertility (N, P, C…)

Crop biomass (DM, N uptake, export)

Drainage (volume, NO3, NH4, DRP, Total P)


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


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…


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)


Above

optimum


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

)


Dra

inage (m

m)

Monitoring period (months)


Measured nitrogen lossesC

um

ula

tive m

inera

l N

losses (

kg/h

a)


What represents an acceptable

environmental loss?


economic loss?


Measured phosphorus lossesC

um

ula

tive T

ota

l P

losses (

kg/h

a)


environmental loss?

Not an economic driver



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…


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?


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.


[email protected]

rootzone reality a fluxmeter network to measure and … · rootzone reality –a fluxmeter network...

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