Results of phosphorus and potassium experiments on Partner Farms of the

Greener Pastures 1 project

Mike Bolland, Plant Nutrition Consultant, Eaton&

Ian Guthridge, Graham Blincow & Peter Needs, DAFWA, Manjimup

Reason for doing the experiments

Continue to improve our knowledge on the phosphorus and potassium requirements of intensively grazed ryegrass dairy pastures.

P experiment

Comprised:

Nil & 3 P levels by 3 methods of application

P level & application methodKg P/ha Method of P application (kg P/ha)

per year All in autumn Half in autumn & spring 1/6 autumn & after first 5 grazings

0

10 1 x 10 = 10 2 x 5 = 10 6 x 1.67 = 10

20 1 x 20 = 20 2 x 10 = 20 6 x 3.33 = 20

30 1 x 30 =30 2 x 15 = 30 6 x 5 = 30

Location of the 3 sites of the phosphorus experiment

• Paddock 41, Mottershead farm, Witchcliffe

• Paddock 38, Evans farm, North Jindong

• Paddock 30, Rodwell farm, Boyanup

Results of the P experiment

Total pasture dry matter consumed 2009, Miles Mottershead, Witchcliffe

0 5 10 15 20 25 300

1

2

3

4

5

6

7

Nil-PAutumnAutumn & springAfter each grazingMean

Kg P/ha applied per year

Past

ure

cons

umed

(t/h

a)

Soil test P (mg/kg) for nil-P treatmentMiles Mottershead, Witchcliffe

2006 2007 2008 2009 20100

10

20

30

40

50

60

70

80

90

f(x) = − 7.1 x + 14318.8R² = 0.980739299610895

PBI = 75 (range 40-114)Critical soil test P (mg/kg) = 30 (15 plots) & 35 (15 plots)

Colw

ell s

oil t

est P

(mg/

kg)

Total pasture dry matter consumed, 2007, Grant Evans, North Jindong

0 5 10 15 20 25 300

1

2

3

4

5

6

7

Nil-PAutumnAutumn & springAfter each grazingMean

Kg P/ha applied per year

Past

ure

cons

umed

(t/h

a)

Soil test P (mg/kg) for nil-P treatmentGrant Evans, North Jindong

2006 2007 2008 2009 20100

10

20

30

40

50

60

70

f(x) = − 4.4 x + 8888.6R² = 0.867383512544803

PBI = 181 (range 124-249)Critical soil test P (mg/kg) = 35 (28 plots) & 40 (2 plots)

Colw

ell s

oil t

est P

(mg/

kg)

Decline in Colwell soil test P (mg/kg per year) when no fertiliser P is applied for a low P sorbing sand (PBI 30) and a high P sorbing

gravel sand (PBI 250)

Years since no fertiliser P applied

Soil

test

P (m

g/kg

) whe

n no

P a

pplie

d

Soil test P (mg/kg) for nil-P treatmentVictor Rodwell, Boyanup

2006 2007 2008 2009 20100

5

10

15

20

25

30

35

40f(x) = − 6.7 x + 13480R² = 0.956734867860209

PBI = 32 (range 19-48)Critical soil test P (mg/kg) = 25 (14 plots) & 30 (16 plots)Co

lwel

l soi

l tes

t P (m

g/kg

)

Total pasture dry matter consumed 2009, Victor Rodwell, Boyanup

0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Nil-PAutumnAutumn & springAfter each grazingMean

Kg P/ha applied per year

Past

ure

cons

umed

(t/h

a)

Pasture consumed at first grazing 2010, Victor Rodwell, Boyanup

0 5 10 15 20 25 300

0.5

1

1.5

2

2.5

3

Nil-PAutumAutumn & springAfter each grazingMean

Past

ure

dry

mat

ter

cons

umed

(t/

ha)

Kg P/ha applied before first grazing in 2010

Published range for critical plant test values for young dried herbage of perennial ryegrass, and plant test values obtained for mixed young annual

and Italian ryegrass dried herbage at the 3 sites of the P experiment

Element Published critical plant

rest value

Witchcliffe N. Jindong Boyanup

P (%) 0.20-0.28 0.52, 0.49 0.42, 0.42 0.50N (%) 3.0-3.5 4.4, 6.0 6.4, 5.1 3.8

K (%) 1.4-1.9 5.2, 5.5 4.6, 4.5 3.6

S (%) 0.18-0.22 0.36, 0.50 0.46, 0.40 0.29

Ca (%) 0.15-0.2 0.47, 0.48 0.61, 0.54 0.65

Mg (%) 0.15-0.2 0.23, 0.24 0.28, 0.25 0.22

Cu (mg/kg) 4.0-6.0 9.9, 12.3 13.2, 8.8 8.4

Zn (mg/kg) 10-15 43, 61 40, 29 25

Mn (mg/kg) 15-20 80, 97 48, 41 108

Fe (mg/kg) 40-60 104, 151 174, 155 189

B (mg/kg) 3.0-5.0 5.4, 7.2 7.6, 6.5 17.3

Conclusions from P experiment

• Only apply fertiliser P when soil test P is below the critical value for that soil

• Applying fertiliser P when soil test P is above the critical value for that soil has no significant effect on pasture production

• When soil test P is well above the critical value and no fertiliser is applied soil test P declines gradually and it takes some time for the soil to become P deficient for pasture production

K experiment

Comprised: Nil & 3 K levels by 3 methods of application

The same K experiment was located at 2 sites:

• Paddock 41, Mottershead farm, Witchcliffe

• Paddock 50, Evans farm, North Jindong

K level & application methodKg K/ha Method of K application (kg K/ha)

per year All in autumn Half in autumn & spring 1/6 autumn & after first 5 grazings

0

50 1 x 50 = 50 2 x 25 = 50 6 x 8.33 = 50

75 1 x 75 = 75 2 x 37.5 = 75 6 x 12.5 = 75

100 1 x 100 =100 2 x 50 = 100 6 x 16.67 = 150

Results of K experiment

Total pasture dry matter consumed 2008, Miles Mottershead, Witchcliffe

0 10 20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

Nil-KAutumnAfter each grazingMean

Kg K/ha applied per year

Past

ure

dry

matt

er c

onsu

med

(t/h

a)

Pasture dry matter consumed at the first 2 grazings in 2010, Miles Mottershead, Witchcliffe

0 10 20 30 40 50 60 70 80 90 1000

0.20.40.60.8

11.21.41.61.8

2

Nil-KAutumnAutumn & springAfter each grazingMean

Kg K/ha applied before first 2 grazings in 2010

Past

ure

dry

matt

er c

onsu

med

(t/h

a)

Published ranges for critical plant test vales for different elements for young tissue of perennial ryegrass, and plant test values for the elements obtained for young tissue of

mixed annual and Italian ryegrass obtained from the K experiment at Witchcliffe for the first 2 grazings in 2010

Element Published critical plant test values

Plant test values obtained at Witchcliffe in 2010

K (%) 1.4-1.9 4.2, 4.8

P (%) 0.2-0.28 0.68, 0.72

N (%) 3.0-3.5 4.6, 6.2

S (%) 0.18-0.22 0.36, 0.53

Ca (%) 0.15-0.20 0.51, 0.56

Mg (%) 0.15-0.20 0.27, 0.24

Cu (mg/kg) 4-6 11, 13

Zn (mg/kg) 10-15 45, 63

Mn (mg/kg) 15-20 76, 74

Fe (mg/kg) 40-60 118, 153

B (mg/kg) 3.0-5.0 5.2, 5.2

Conclusions from K experiment

• Fertiliser K is usually only required for clover in the traditional clover ryegrass pastures

• Fertiliser K is rarely required for ryegrass pastures, except after silage or hay crops

• Apply fertiliser K when there is less than 2% K in young clover or ryegrass herbage collected 5 cm above the soil surface just before grazing

• Applying fertiliser K to ryegrass pastures when it is not required will have no effect on ryegrass dry matter production and may adversely affect cow health (inducing magnesium deficiency in cows)

General conclusions

• Apply phosphorus fertiliser when soil testing indicates it is required

• Apply potassium fertiliser when plant testing indicates it is required

Phosphorus Buffering Index (PBI) of soil and corresponding Critical Colwell soil test phosphorus

PBI(no units)

Critical Colwell soil test phosphorus(mg/kg)

5-10 15

11-15 20

16-30 25

31-70 30

71-140 35

141-280 40

Subterranean clover, top 10 cm of soil

0

1

2

3

4

5

6

0 50 100 150 200 250

Colwell soil test K (mg K/kg soil)

DM

resp

onse

to a

pplie

d K

(t/h

a)

Greener Pastures

Critical potassium level for clover

Annual ryegrass, top 10 cm of soil

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 50 100 150 200 250

Colwell soil test K (mg K/kg soil)

DM

resp

onse

to a

pplie

d K

(t/h

a)

Greener Pastures

Critical potassium level for ryegrass

Colwell soil test K measured in nil-K plots and plots receiving 100 kg K/ha per year, K experiment, Mottershead farm, Witchcliffe

Kg K/ha per year

Method of Kapplication

2007 2008 2009 2010

0 65 43 70 101

0 143 46 82 53

0 94 136 84 49

100 Autumn 127 54 93 77

100 Autumn 91 66 77 85

100 Autumn 83 155 92 41

100 Autumn & spring 111 52 119 107

100 Autumn & spring 92 81 109 58

100 Autumn & spring 188 64 83 50

100 After grazing 98 80 109 113

100 After grazing 117 96 82 57

100 After grazing 76 106 75 45

Relationship between percentage of the maximum (relative) plant yield and either P level applied or soil test P for a low P sorbing sand (PBI 30) and high P

sorbing lateritic gravel sand (PBI 250)

Kg P/ha appliedSoil test P (mg/kg)

Rela

tive

plan

t yie

ld (%

)

Maximum yield plateau

100

50

0

95% OF THE MAXIMUM YIELD

75

25