A Modelling Approach to Explore the Impact of Root Distribution and Citrate Release on Phosphorus Use Efficiency of Crops

Sustainable Agriculture Flagship

Enli Wang, Brad Ridoutt

Zhongkui Luo, Ulrike Bende-Michl

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

Crops

System ControlSystem Control

SoilSoil

SWIM

ManagerReportClock

SoilWat

Soil C & N

SoilPH

SoilP

ResidueEconomics

Fertiliz

Irrigate

Canopy Met

Erosion

Other Crops

Maize

Sorghum

Legume

Wheat

New Module

Manure

SWIM

ManagerReportClock

SoilWat

Soil C & N

SoilPH

SoilP

ResidueEconomics

Fertiliz

Irrigate

Canopy Met

Erosion

Other Crops

Maize

Sorghum

Legume

Wheat

New Module

Manure

ManagerReportClock

SoilWat

Soil C & N

SoilPH

SoilP

ResidueEconomics

Fertiliz

Irrigate

Canopy Met

Erosion

Other Crops

Maize

Sorghum

Legume

Wheat

New Module

Manure

ManagementManagement

ENGINE

ENGINE

1.1 APSIM

• APSIM: Agricultural Production Systems Simulator

• A modular modelling

framework

• Simulates biophysical

processes in farming

systems

• Links to economic &

ecological outcomes of

management practices under

climate variation

1.1 APSIM

APSIM is a farming systems model, able to simulate

• >20 crops, including pastures & trees• complex rotation patterns• water, carbon, nitrogen and phosphorus

cycling

1.2 Crop Modules

• Potential growth of crops

• P demand based on critical P concentrations,

biomass & new growth

• Reduction in growth due to P deficiency

1.3 SoilP Module

P fertilizerbroadcast

UnavailableInorganic P

Rock PUnavailableOrganic P

Labile P

P in Soil solution

Crop P Uptake

Ads

orpt

ion

Des

orpt

ion

MineralizationImmobilization

Dissolution

Placement effect

P fertilizer banded

APSIM-SoilP:• does not simulate • precipitation/dissolution

of tightly bonded soil P• may not work in acidic

soils (pH<5.5) and alkaline soils (pH>7.3)

• new development is on-going for P modeling in those soils

• original version does not consider effect of root exudation on PUE

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

2.1 Process understanding and data availability

• Organic anions can enhance P mobilisation into soil solution (Jones,

1998; Khademi et al, 2010)

• Release of citrate, malate & oxalate from roots increases with P

deficiency (Vance et al, 2003; Ryan et al, 2001)

Crop Citrate Efflux References(nmol/gFW/h)

Rice 155~360 Kirk et al (1999)Wheat 5~185 Ryan et al (2009)

White lupin 1656~2373 Roelofs et al (2001)Proteaceae 3600~9000 Roelofs et al (2001)

Table 1 citrate efflux from plant roots

2.2 Modelling

• Only one modeling study to simulate rice P uptake

in controlled laboratory experiment

• Rice (Kirk et al, 1999) – diffusion,

decomposition and P solubilisation of citrate,

only a few mm around roots, no zero efflux

treatment

• No field scale modelling studies so far

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

3.1 APSIM enhancements

1. Original Model: crop P uptake is linked to solution P in rooted soil layers

2. Enhancement #1: need to link crop P uptake to solution P and root length density (RLD)

3. Enhancement #2: need to link crop P uptake & solution P to citrate efflux from roots

(Fc)

P fertilizerbroadcast

UnavailableInorganic P

Rock PUnavailableOrganic P

Labile P

P in Soil solution

Crop P Uptake

Ad

sorp

tion

Deso

rpti

on

MineralizationImmobilization

Dissolution

Loss of availability

Gain of availability

Placement effect

P fertilizer banded

P released by citrateP released by citrate

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

4.1 Biomass

1. Original Model: crop P uptake is linked to solution P in rooted soil layers

Comparison of simulated and observed wheat grain yields under different levels of P fertiliser inputs at one QLD site and two NSW sites.

The modified model performed slightly better than the original one!

y = 1.1742x - 259.46R2 = 0.896

0

1000

2000

3000

4000

5000

6000

7000

0 10002000 3000 4000 5000 60007000Observed wheat yield (kg/ha)

Sim

ulat

ed w

heat

yie

ld (

kg/h

a)

(b) APSIM-SoilP&RLD

y = 1.1256x + 10.593R2 = 0.8891

0

1000

2000

3000

4000

5000

6000

7000

0 1000 2000 30004000 50006000 7000Observed wheat yield (kg/ha)

Sim

ulat

ed w

heat

yie

ld (

kg/h

a)

(a) APSIM-SoilP

2. Enhancement #1: need to link crop P uptake to solution P and root length density (RLD)

4.2 Scenario analysis

• Study site: Kingaroy, QLD (1957-2009)• Cropping system: Continuous wheat, rainfed condition• Citrate efficiency = 0.4• Five levels of soil P sorption capacity:

• Low 50, 100• Medium 200• High 500• Very high 1000

• Seven levels of citrate efflux (nmol/gFW/h): 0, 50, 100, 200, 500, 1000, 2000

• 11 levels of P application rates (kg P/ha): 0~200 kg P/ha with increase of 20 kg P/ha.

4.3 Biomass responses: short-term vs long-term

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

(a) Citrate efflux = 0 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (k

g/ha

)

(b) Citrate efflux = 200 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

(c) Citrate efflux = 1000 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

501002005001000

Sorption:

(d) Citrate efflux = 2000 nmol/gFW/h

First year 1957

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

501002005001000

Sorption:

(a) Citrate efflux = 0 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

501002005001000

Sorption:

(b) Citrate efflux = 200 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

501002005001000

Sorption:

(c) Citrate efflux = 1000 nmol/gFW/h

0

4

8

12

16

20

0 40 80 120 160 200P Rate (kg/ha)

Bio

mas

s (t

on/h

a)

501002005001000

Sorption:

(d) Citrate efflux = 2000 nmol/gFW/h

Average 1957~2009

0

5

10

15

20

25

1950 1960 1970 1980 1990 2000 2010

Year

Bio

mas

s or

gra

in y

ield

(to

n/ha

)

Biomass

Yield

(a) Citrate Eff lux = 0 nmol/gFW/h

0

5

10

15

20

25

1950 1960 1970 1980 1990 2000 2010

Year

Bio

mas

s or

gra

in y

ield

(to

n/ha

)

Biomass

Yield

(b) Citrate Eff lux = 200 nmol/gFW/h

0

50

100

150

200

1950 1960 1970 1980 1990 2000 2010Year

Tot

al in

orga

nic

soil

P (

kg/h

a) Layer 1Layer 2Layer 3

(d) Citrate Eff lux = 200

0

50

100

150

200

1950 1960 1970 1980 1990 2000 2010Year

Tot

al in

orga

nic

soil

P (

kg/h

a) Layer 1Layer 2Layer 3

(c) Citrate Eff lux = 0

4.4 Biomass, yield and inorganic soil P

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Citrate efflux (nmol/gFW/h)

P r

ate

re

qu

ire

d fo

r 9

0%

ma

x b

iom

ass

(kg

/ha

) SP50

SP100SP200

SP500SP1000

4.5 P rate required for 90% max biomass

0

20

40

60

80

100

120

140

160

180

0 500 1000 1500 2000Citrate efflux (nm/g/h)

Sorption = 50Sorption = 200Sorption = 500Sorption = 1000

(c) P Rate = 60 kg/ha

0

20

40

60

80

100

120

140

160

180

0 500 1000 1500 2000Citrate efflux (nm/g/h)

(b) P Rate = 40 kg/ha

0

20

40

60

80

100

120

140

160

180

0 500 1000 1500 2000Citrate efflux (nm/g/h)

P r

eco

very

(%

)

(a) P Rate = 20 kg/ha

4.6 P recovery

Outline of the presentation

1. APSIM and its capability to simulate crop response to soil P

2. Current understanding and available data on citrate release from plant roots and its impact on PUE

3. New model development to enable APSIM to simulate impact of citrate efflux on PUE

4. Simulated response of wheat growth and P uptake to citrate effluxes

5. Summary

5. Summary

Long-term effect is different from short-term effect, due to residual effect of applied P.

Major impact is to increase PUE of applied P fertilisers, because soil P reserve can be depleted in a relatively short time period.

P rate required to achieve maximum crop yield decreases with increasing citrate efflux from the roots.

The impact increases with soil P sorption capacity, decreases with P application rate.

Thank you