Nitrogen mineralisation and impacts on

fertiliser efficiency in pastures

Helen Suter, Oxana Belyaeva, Graeme Ward, Yong Li

IPL Agronomy Forum, 20th July, 2018

Motivation for Research Program

• SW Vic, average 40 kg N/ ha/ application = 200 - 480 kg N/year depending

on dryland / irrigated

• or 1-2 kg N/ha/day

• + 1000 kg N/ha as urine (20% coverage)

• + manure (3% N)

Q: Is there too much N going into dairy pasture, how much is stored, and

can we reduce the fertiliser inputs by using soil stored N?

High Inputs of Nitrogen into dairy pastures

Motivation for Research Program

Autumn Spring

Agronomic N efficiency(kg pasture increase per kg N applied)

8 18

Apparent recovery efficiency (%)(net kg of N taken up per kg N applied)

34 76

Low nitrogen use efficiency from urea

Suter et al. (2013) Nutrient Cycling in Agroecosystems

Ammonia volatilisation – up to 30%

Example: Research at Murroon, SW Vic

Q: Can we reduce N inputs and improve NUE without affecting productivity?

Motivation for Research Program

0

10

20

30

40

50

60

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

Gro

wth

rate

(kg

DM

/ha

/da

y)

Grass N

demand

Clover potential

??

Autumn

Break

Variable seasonal pasture growth

Eckard (1998) A critical review of research on the nitrogen nutrition of dairy pastures in Victoria

Q: Can we modify N fertilisers in line with the plant growth requirements and

use soil N in its place at key times?

0

1

2

3

4

5

6

0 20 40 60 80

Bio

mas

s (t

/ha)

N rate (kg / ha)

Irrigated

15/02/17 27/04/17 6/06/2017

Motivation for Research Program

summer autumn winter

Variable seasonal nitrogen response curves

Q: Could the reason for a flat autumn N response be mineralisation with

autumn rains?

Motivation for Research Program

0

10

20

30

40

50

60

70

80

0 20 40 60 80

Soil

dep

th (

cm)

Total C and N (t/ha)

TC-dryland

TN-dryland

TC-irrigated

TN-irrigated

Mineral N-dryland

Mineral N-irrigated

Profile total 229 t/ha

15.5 t/ha

174 t/ha

13.2 t/ha

90 kg N/ha

50 kg N/ha

0.6% of TN

0.4% of TN

Example: SW Vic - Autumn soil

nitrogen supply in the profile

Mineral N (kg N/ha)

High organic matter content

C:N

15:1

13:1

Investigation of Mineralisation

• Q: Can the soil organic matter pool be effectively utilised for N nutrition?

• Q: Is it possible to drop N rates at particular times of the year without

impacting biomass response at the time and into the future?

• Q: Can we estimate the amount of N that is likely to be provided from soil

mineralisation at these times?

Research Program

• Two small plot trials operating at 1 farm

–Dryland and Irrigated

• Site: Mepunga West, SW Victoria

• Perennial ryegrass dominant pastures

• N response trials (urea: 0, 20, 40, 60, 80 kg N/ha) + urine

Research Program

• 1.5 years

• Pasture biomass and N

• Stock exclusion, full removal

• Soil total C and N, mineral N

• Soil and ambient moisture, temperature

Research Program: NUE assessment

• 15N techniques

•Modelling

• Potentially mineralisable N

Nitrogen Response : Irrigated

0

1

2

3

4

5

6

7

0 20 40 60 80

Past

ure

her

bag

e d

ry m

atte

r (

t D

M/h

a)

N rate (kg N/ha)

9/01/18

15/02/17

19/12/17

17/01/17

a) summer

0

1

2

3

4

5

6

7

0 20 40 60 80

Past

ure

her

bag

e d

ry m

atte

r (

t D

M/h

a)

N rate (kg N/ha)

8/03/17

4/04/17

27/04/17

b) autumn

0

1

2

3

4

5

6

7

0 20 40 60 80

Past

ure

her

bag

e d

ry m

atte

r (

t D

M/h

a)

N rate (kg N/ha)

01/08/17

6/06/17

c) winter

0

1

2

3

4

5

6

7

0 20 40 60 80

Past

ure

her

bag

e d

ry m

atte

r (t

DM

/ha)

N rate (kg N/ha)

14/10/17

01/11/17

22/11/17

d) spring

Nitrogen Use Efficiency: Urea – annual (20-80 kg N/ha)

Dryland Irrigated

Av. Min. Max. Av. Min. Max.

Total N applied (kg/ha) - 140 560 - 240 960

Annual Biomass Control

(t DM /ha)17 - - 21 - -

Annual Biomass Fertiliser

(t DM/ha)24 21 27 40 29 47

Annual N removed in

Control (kg N/ha)562 - - 656 - -

Annual Nitrogen Use

Efficiency

(Net-nitrogen removed /N

input)

0.83 0.75 0.95 0.90 0.74 1.02

Annual Agronomic

Nitrogen Use Efficiency

(kg DM / kg N)21 15 26 27 22 32

Soil supply of N : 15N results, 4/04/17 application

Soil supply of N : 15N results Autumn break (late-April)

Soil supply of N : 15N results, 4/04/17 application

Soil supply of N : 15N results Autumn break (late-April)

N rate (kg N/ha)

Dry matter (t/ha)

N removedby pasture

(kg/ha)

15N recovery

(%)Ndff (%) Ndfs (%)

Dryland

10 1.2 44 23 18.3 81.7

20 1.1 40 23 38.2 61.8

40 - - - - -

Irrigated

10 0.7 27 18 5.9c 94.1a

20 1.0 39 24 11.0b 89.0b

40 1.1 45 25 20.5a 79.5c

Ndff : Nitrogen derived from fertiliser Ndfs: Nitrogen derived from soil

Potentially mineralisable N (PMN)

Acknowledgement: Phil Moody, Qld Department of Environment and Science

Date Location

TC TN PMN (0-10 cm)

(%) (%)(mg/

kg soil)(kg /ha)

April-2017

Dryland 4.09 0.31 113.1 147.0

Irrigated 3.37 0.27 95.5 114.6

Nov-2017Dryland 3.37 0.25 44.9 58.4

Irrigated 3.46 0.27 79.7 95.6

Potentially mineralisable N (PMN)

*BD 1.3 g/cm3 and 1.2 g/cm3 for dryland and irrigated systems respectively

Acknowledgement: Phil Moody, Qld Department of Environment and Science

Date Location

TC TN PMN (0-10 cm)

(%) (%)(mg/

kg soil)(kg /ha)

% of TN

April-2017

Dryland 4.09 0.31 113.1 147.0 3.7

Irrigated 3.37 0.27 95.5 114.6 3.5

Nov-2017Dryland 3.37 0.25 44.9 58.4 1.8

Irrigated 3.46 0.27 79.7 95.6 2.9

Potentially mineralisable N (PMN)

Acknowledgement: Phil Moody, Qld Department of Environment and Science

Date Location

PMN (0-10 cm)

TN removed(15N studies)

Ndfs(15N studies)

(kg /ha)@ 20 kg

N/ha (kg/ha)

@ 40 kg N/ha

(kg/ha)

@ 20 kg N/ha

(kg/ha)

@ 40 kg N/ha

(kg/ha)

April-2017

Dryland 147.0 40 - 25 -

Irrigated 114.6 39 45 35 36

17 - 31% of the PMN taken up by the plant over 23 days of growth

0

5

10

15

20

25

30

35

40

45

50

Jan

_201

7

Feb

_201

7

Mar

_201

7

Ap

r_20

17

May

_20

17

Jun

_201

7

Jul_

2017

Au

g_20

17

Sep

_201

7

Oct

_201

7

No

v_20

17

Mo

del

led

gro

ss m

iner

alis

atio

n

(kg

N/h

a/m

on

th)

Dry-control

Dry-U40

irrig-control

irrig-U40

Climate influences : Estimation of mineralisation

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Ambient oC 23 23 25 19 16 14 13 13 15 18 23

Rain (mm) 53 55 60 75 37 24 65 56 72 43 24

Rain + irrig (mm) 164 157 137 105 54 35 99 100 170 100 217

TC1 TN1 (0-10 cm)

4.6% 0.36%

3.8% 0.32%

0

5

10

15

20

25

30

30

/01

/17

1/0

3/1

7

31

/03

/17

30

/04

/17

30

/05

/17

29

/06

/17

29

/07

/17

28

/08

/17

27

/09

/17

27

/10

/17

26

/11

/17

26

/12

/17

Tem

per

atu

re (

oC

)

Top 20 cm

0

5

10

15

20

25

30

35

40

0

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30

40

50

60

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100

30

/01

/17

1/0

3/1

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31

/03

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30

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29

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29

/07

/17

28

/08

/17

27

/09

/17

27

/10

/17

26

/11

/17

26

/12

/17

Rai

nfa

ll (m

m)

Soil

mo

istu

re (

m3

m-3

)

rainfall Irrigated 10 cm

Dryland 10 cm Irrigated 20 cm

Dryland 20 cm

Soil

temperature

& moisture

Soil supply of N : 15N results, 4/04/17 application

Annual N removal from irrigated pasture

0

20

40

60

80

100

120

140

160

180

200

15

/01

/20

17

6/0

3/2

017

25

/04

/20

17

14

/06

/20

17

3/0

8/2

017

22

/09

/20

17

11

/11

/20

17

31

/12

/20

17

19

/02

/20

18Nit

roge

n r

emo

ved

in b

iom

ass

(kg

N/h

a)

Control Urea - 40 kg N/ha

Control + 40 kg N/ha

Nitrogen

added to soil

from urea

656 kg

N/ha

1270 kg

N/ha

= 480 kg N/ha

Conclusions

• Q: Can the soil organic matter pool be effectively utilised for N nutrition?

Modelled estimates are <1% of total N is mineralised annually

Autumn

• PMN supply 115-147 kg N/ha

• > 60% of the N taken up by plants over 23 days comes from soil

= 25-36 kg N/ha

YES: The soil organic pool can supply N to pastures

Conclusions

• Q: Is it possible to drop N rates at particular times of the year without

impacting biomass response at the time and into the future?

• YES: In autumn flat responses indicate that N fertiliser could be dropped

without impact on biomass

+ Improvements in NUE

• However: Long term impacts are not known at this stage and additional N

supply later may be required.

- Small plot trial shows N mining from soil

- No animal and pasture returns

Conclusions

• Q: Can we estimate the amount of N that is likely to be provided from soil

mineralisation at these times?

• A WORK IN PROGRESS:

PMN values obtainable but climate and soil conditions will influence

mineralisation

Good first estimates from model of mineralisation

25-36 kg N/ha supplied in April -2017

N2 fixation contribution unknown

Thusari Andrew Oxana Graeme Arjun

This project is supported by funding from the Australian Government Department of Agriculture and WaterResources as part of its Rural R&D for Profit program, The University of Melbourne and Dairy Australia

Thankyou

Acknowledgments: Deli Chen, Jim He

Nitrogen Balance : Irrigated

• Excess N being removed from soil

• Seasonal effect

• Possible replenishment from i) N2 fixation = 550-650 kg N/ha/yr (dryland 350-550)

ii) Animal inputs (outside of plots) = 400 kg N/ha/event (localised)

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

Net

N (

N a

dd

ed-N

rem

ove

d)

(kg

N/h

a)

21/11/16 15/02/17 8/03/2017 4/04/2017 27/04/2017 6/06/2017 1/08/2017

14/10/2017 1/11/2017 22/11/2017 19/12/2017 19/01/2018 19/02/2018 14/03/2017

C 20 kg N/ha 40 kg N/ha 60 kg N/ha 80 kg N/ha

0

5

10

15

20

25

30

35

0.0

0.1

0.2

0.3

0.4

0.5

0.6

4/0

4/2

01

7

18

/04

/20

17

2/0

5/2

01

7

16

/05

/20

17

30

/05

/20

17

13

/06

/20

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27

/06

/20

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11

/07

/20

17

25

/07

/20

17

8/0

8/2

01

7

22

/08

/20

17

5/0

9/2

01

7

19

/09

/20

17

3/1

0/2

01

7

17

/10

/20

17

31

/10

/20

17

14

/11

/20

17

28

/11

/20

17

Rai

nfa

ll (m

m)

and

air

tem

pe

ratu

re (o

C)

Soil

mo

istu

re (

m3/m

3)

rainfall Control U80 Fertiliser Max air temp.

Soil moisture and treatment : Dryland site topsoil (0-6 cm)

Potentially mineralisable N (PMN)

*BD 1.3 g/cm3 and 1.2 g/cm3 for dryland and irrigated systems respectively

Acknowledgement: Phil Moody, Qld Department of Environment and Science

Date Location

TC TN PMN (0-10 cm)

(%) (t/ha)* (%) (t/ha)*(mg/

kg soil)(kg /ha)

% of TN

April-2017

Dryland 4.09 53 0.31 4.0 113.1 147.0 3.7

Irrigated 3.37 40 0.27 3.3 95.5 114.6 3.5

Nov-2017

Dryland 3.37 44 0.25 3.3 44.9 58.4 1.8

Irrigated 3.46 42 0.27 3.3 79.7 95.6 2.9