Grazing strategies and timing of stock removal from dual purpose cereals and canola

Take home message

Timing of lock up and residual biomass influence grain yield recovery in both cereals and canola.

Early lock-up enables a crop sufficient time to achieve biomass levels at flowering to fully recover grain yield but lower residual biomass at lock-up can reduce crop recovery during a sensitive window around or shortly after GS30 in cereals and bud visible in canola.

Light defoliation with sufficient residual biomass even after GS30 can allow cereal crops to fully recover grain yield in some seasons.

To avoid risk of yield loss in canola, residual biomass levels greater than 2.5 t DM/ha are required if grazing continues after late July. A similar critical level is less clear in cereals but appears to be about 1-1.5 t DM/ha required at lock-up in mid-August.


Introduction


Dual-purpose crops hold great potential to utilise early season sowing opportunities and provide grazing for livestock and later yield grain. The period of grazing can increase net crop returns by up to $600-900/ha (i.e. 2000-3000 sheep grazing days at 28c/day) and have a range of systems benefits including weed management, reducing crop height and enabling pastures to be spelled during this period.

 Grazing can have both positive and negative effects on subsequent grain yield. Positive effects can occur under dry seasonal conditions where grazing reduces crop canopy and slows water use to be used later to fill grain more effectively. Large reductions in subsequent crop yields are reported to occur when grazing continues into an ‘unsafe’ period after the initiation of reproductive stem elongation (GS30 in cereals or stem elongation in canola), primarily by reducing tiller numbers and hence grain number in the regrowing crop for cereals and delaying the onset of flowering in canola (Fig. 1). On the other hand, when grazing stops sufficiently early this allows sufficient time for the crop to recover critical biomass and leaf area to achieve its similar grain yields to ungrazed crops (Fig 1). However, we believe there is a ‘sensitive’ window when the crop may still be grazed but sufficient residual biomass is required to allow the crop to reach its critical biomass or leaf area to achieve potential grain yields. Crops with low levels of residual biomass after grazing may not have sufficient time to recover to this critical level and hence will suffer a yield penalty from grazing. In this paper we present some results of recent experiments where we explore this effect and discuss the implications for grazing management of dual-purpose crops to maximise their yield recovery.

Here we firstly present some results form an experiment conducted at Greenethorpe, NSW in 2013 where a range of mechanical defoliation intensities (hard cut – 5 cm, moderate cut – 8 cm and ‘clip’ cutting – removing leaves) and lock-up timings were imposed to explore their impact on yield recovery in a winter and spring wheat and canola.  This experiment received 270 mm of growing season rainfall (Apr-Oct) after 88 mm in March, but experienced a very dry spring which limited grain yield potentials.

Bell Well 1

Figure 1. Yield recovery (% of ungrazed crop) of grazed dual-purpose crops highlighting the safe, sensitive and unsafe periods of grazing. Early lock-up in the ‘safe’ period allows sufficient time to fully recover grain yield,  during the ‘sensitive’ period yield recovery is affected by residual biomass at lock-up and late grazing in the ‘unsafe’ period reduces grain yield recovery by removing heads.

Wheat - effect of lock-up time and residual biomass

Firstly, it should be noted that the earlier sown winter wheat was able to out-yield the later sown spring wheat, and provided large amounts of biomass and potential economic gains from grazing.

In the winter wheat EGA Wedgetail sown 15 March, early defoliation prior to GS30 (2 July) had no negative effects on grain yield irrespective of the residual biomass remaining (Table 1). However after this time the crop moved into a sensitive period (mid-July), where residual biomass greatly influenced yield recovery. Lightly grazed or defoliated crops with residual biomass >1.5t/ha were able to recover to achieve grain yields equal to ungrazed crops, while crops that were more intensely defoliated and had lower residual biomass were less able to recover grain yield. For example, the hard cutting treatment on 15 July (GS32) had 0.6 t DM/ha residual biomass suffered a 25% reduction in grain yield probably due to the removal of heads by defoliation, while the light cutting treatment suffered no significant grain yield penalty. Even the triple cut treatment which took longer to reach GS30  but had low levels of residual biomass (0.2 t/ha)at this time also suffered a 20% yield penalty despite the fact that no heads were removed

In contrast to EGA Wedgetail, the spring variety EGA Gregory sown 8 May suffered no yield penalties under any of the defoliation treatments, even those which were imposed after GS30 and had low levels of residual biomass. The seasonal conditions with a dry spring limited the yield potential in the uncut treatment (grain filling was hindered, resulting in smaller grains) and the defoliated crops were able to compensate to produce similar grain yields, even though their grain number was reduced. Under   more favourablespring grain filling conditions  where the uncut crop was able to fill its grains, larger yield penalties from late and intense defoliation may be likely.

Table 1. Effect of mechanical defoliation treatments on removed dry matter (DM), residual dry matter, grain yield recovery and relative economics compared to a grain-only control in EGA Wedgetail winter wheat sown 25 March and EGA Gregory spring wheat sown 8 May at Greenethorpe, NSW in 2013. Optimal economic outcomes are highlighted in grey.

Var.

Lock-up time

Cutting intensity treatment

Removed DM (t/ha)

Residual DM (t/ha)

Grain yield (t/ha)

Relative Yield (% of uncut)

Relative economics ($/ha)

EGA Wedgetail

UNCUT



4.35



Z30

(2 Jul)

Clip

1.0

2.7

4.66

107

+328

Moderate

2.5

1.2

4.44

102

+648

Hard

2.6

1.1

4.36

100

+653

Z32

(15 Jul)

Clip

3.3

1.4

4.19

96

+785

Moderate

3.8

0.9

3.96

91

+853

Hard

4.1

0.6

3.28

75

+758

15 Jul

Triple (+Z14+Z30)

3.0

0.2

3.47

80

+530

6 Jul

Grazed

2.0

2.4

4.30

99

+488

Grazed+mow

2.6

1.7

3.95

91

+550

EGA Gregory

UNCUT



3.58



Z14

Hard

0.3

0.1

3.67

102

+98

Z30

(15 Jul)

Clip

0.1

0.5

3.59

100

+27

Moderate

0.3

0.3

3.51

98

+57

Hard

0.4

0.2

3.69

103

+128

Z32

(30 Jul)

Clip

0.6

1.0

3.47

97

+123

Moderate

1.0

0.6

3.91

109

+333

Hard

1.2

0.4

3.45

96

+268

30 Jul

Double moderate (Z30+Z32)

0.6

0.5

3.72

104

+185

20 Jul

Grazed

0.4

0.2

3.74

104

+140

Economics calculated at $250/t grain and biomass removed at $0.25/kg (i.e. $1.7/kg LW for a sheep growing at 225g/day and eating 1.5kg biomass/animal/d)

Figure 2 shows the regrowth of crops after defoliation relative to the uncut control in both EGA Wedgetail and EGA Gregory. This shows that EGA Wedgetail crops that were cut later and had less residual biomass suffer a significant reduction in crop biomass by anthesis. Those crops that failed to reach a critical anthesis biomass level (estimated to be about 8.5 t/ha in that particular growing season) suffered a significant yield penalty. That is,the late and hard defoliation in EGA Wedgetail only reached 7-8 t DM/ha by anthesis and hence suffered significant yield penalties (>15%). On the other hand, in EGA Gregory the crops were able to recover to achieve anthesis biomass sufficient to produce similar yields to uncut crops even from late defoliation treatments.  A higher critical anthesis biomass threshold may be needed in seasons with higher yield potential, and in these seasons defoliated crops may not be able to ‘catch up’.

Bell Well 2

Figure 2. Regrowth of biomass in EGA Wedgetail and EGA Gregory wheat after defoliation until anthesis at Greenethorpe in 2013. Dotted line indicates the critical anthesis biomass (8.5 t DM/ha) required to achieve yield potential in 2013.

Canola - effect of lock-up time and residual biomass

Similar results to those discussed in wheat were observed in canola with both defoliation timing and intensity influencing yield recovery (Table 2). Again, the winter canola variety (Hyola 971) sown 25 March had similar grain yields to the spring variety (Hyola 575) sown 23 April but provided large amounts of grazing and significant economic advantage.

In canola, both the winter and spring cultivars suffered yield penalties when defoliated late and hard. Yield penalties of 20-30% were seen when crops were severely defoliated (less than 1. 0 t DM/ha remaining) after the bud had elongated 10 cm. However, less severe defoliation treatments with higher residual biomass (> 2.5 t/ha) were able to recover to produce similar grain yield to the uncut control. In contrast to the cereals, yield penalties were evident from hard defoliation which occurred before stem elongation or bud visible (equivalent of GS30 in cereals). For example in both cultivars, the hard defoliation treatment occurring at bud visible (BV) resulted in a 20% yield penalty, while the less severe defoliation treatments were able to fully recover grain yield.

Table 2. Effect of defoliation treatments on removed DM, residual DM, grain yield recovery and relative economics compared to a grain-only control in Hyola® 971 winter canola sown  25 March and Hyola 575 spring canola sown 23 April at Greenethorpe in 2013. Optimal economic outcomes are highlighted in grey.

Var.

Lock-up time

Cutting intensity treatment

Removed DM (t/ha)

Residual DM (t/ha)

Grain yield (t/ha)

Relative Yield (% of uncut)

Relative economics ($/ha)

Hyola 971

UNCUT



2.79



6-8 leaf

(7 May)

Hard

0.9

0.4

2.90

104

+280

BV

(19 June)

Double (+6-8lf)

3.6

0.9

2.16

77

+585

Hard

3.1

1.2

2.44

87

+600

BV10

(24 Jul)

Double (+6-8lf)

2.4

2.6

2.59

93

+500

Hard

2.4

3.0

2.55

91

+480

BV20

(6 Aug)

Double (+6-8 leaf)

3.8

3.6

2.77

99

+940

Double (+BV)

3.9

1.9

2.43

87

+795

Triple (+6-8lf+BV)

4.4

1.6

2.37

85

+890

Moderate

1.9

5.3

2.88

103

+520

Hard

4.5

2.7

2.24

80

+850

6 July

Grazed

5.6

0.4

2.04

73

+1025

Hyola 575

UNCUT



2.82



6-8 leaf

(17 Jul)

Hard

0.7

0.2

2.55

91

+40

BV

(24 Jul)

Clip

0.1

1.3

3.09

110

+160

Moderate

0.2

1.2

3.01

107

+145

Hard

0.8

0.6

2.29

81

-65

BV10

(30 Jul)

Light

0.8

1.4

2.63

93

+105

Moderate

1.1

1.0

2.78

99

+255

Hard

1.4

0.7

1.99

71

-65

BV20

(6 Aug)

Light

0.4

3.1

2.58

91

-20

Hard

1.3

1.2

2.02

72

-75

30 Jul

Grazed

0.9

0.2

2.13

76

-120

Economics calculated at $250/t grain and biomass removed at $0.25/kg (i.e. $1.7/kg LW for a sheep growing at 225g/day and eating 1.5kg biomass/d) are relative to the uncut control.

As in the cereals, Figure 3 shows the regrowth of crops after defoliation relative to the uncut control in both winter and spring cultivars. Hyola 971 crops that were cut later and had less residual biomass  suffered a significant reduction in crop biomass by the start of flowering. Those crops that suffered a significant yield penalty were those that failed to reach a critical biomass level (estimated to be about 8 t/ha in that particular growing season). This explains the yield penalties observed even in crops that were defoliated in the period that is generally considered to be ‘safe’. For example, in both cultivars the treatments that suffered a 20% yield penalty after a severe defoliation before bud visible failed to reach this critical biomass threshold, meanwhile crops recovering from a higher residual biomass were able to reach this critical biomass and hence fully recover grain yield.

Bell Well 3

Figure 3. Regrowth of biomass in EGA Wedgetail and EGA Gregory wheat after defoliation until anthesis at Greenthorpe in 2013. Dotted line indicates the critical biomass required to achieve yield potential in 2013.

Grazing canola does involve some potential risks for animal health, particularly nitrate poisoning if grazing crops grown under high fertility and hence vigilance is required. Follow recommendations for grazing forage brassicas. There is also often a 10-14 day lag in animal growth rates as they become accustomed to grazing canola; hence, extending grazing periods by moving animals between canola paddocks is likely to provide greatest value.

How do these results compare with experiments in the Central West?

Table 3 and 4 present results of an experiment conducted at Coolah in 2013 where 3 winter and 3 spring cereal varieties and 2 winter and 2 spring canola varieties were defoliated at different times and intensities to investigate the impacts on yield recovery compared to ungrazed crops. Crops were either grazed for 5 days up to 5 September or were cut mechanically to 6-8 cm height to correspond to GS30 (though this did occur after GS30 for some varieties).

Table 3. Effect of lock-up time and residual biomass on yield recovery in winter and spring cereals at Coolah, 2013. Grazing ceased on 5 September (GR) and cutting  (C) of winter varieties on 14 Aug and spring varieties on 29 Aug. Large yield penalties are highlighted in grey.


TRT

Winter Varieties

Spring Varieties

 

EGA Wedgetail

SQP Revenue

Urambie

EGA Gregory

Bolac

Oxford

 

Growth stage at 'lock-up'

GR

>GS30

V

>GS30

GS30

V

>GS30

C

>GS30

V

>GS30

GS30

V

>GS30

Residual biomass (t/ha)

GR

3.35

2.14

4.43

1.23

0.91

1.60

 

C

0.90

0.80

1.45

0.54

0.57

0.88

 

Grain yield (t/ha)

UN

4.15

4.04

4.82

4.44

4.04

5.08

 

Change in GY (t/ha)

GR

-1.16

+0.88

-1.48

-0.40

-0.08

-1.60

 

C

-2.93

+0.11

-2.56

-0.57

-0.01

-1.23

 

Relative yield (% of uncut)

GR

72

122

69

91

99

69

 

C

29

103

47

87

100

76

 













Table 4. Effect of lock-up time and residual biomass on yield recovery in winter and spring canola at Coolah, 2013. Grazing (GR) ceased on 5 September and cutting (C) was conducted on 12 Sep.

TRT

Winter Varieties

Spring Varieties

Hyola 971

Hyola 930

Hyola 575

Garnet

Growth stage at 'lock-up'

GR

BV5

BV10

BV20

BV20

C

BV15

BV20

BV35

BV30

`Residual biomass (t/ha)

GR

3.45

3.75

0.66

1.37

C

1.91

2.26

1.09

1.20

Grain yield (t/ha)

UN

1.40

1.34

0.77

1.15

GR

1.49

1.28

0.29

0.89

C

0.91

0.96

0.41

0.65

Relative yield (% of uncut)

GR

106

96

54

77

C

65

72

38

56









These results are consistent with findings from the Greenethorpe experiment discussed above:

  • Winter and spring varieties achieved similar yield potentials; though it is worth noting that both sets of varieties were sown late which probably hindered yield potential in that season.
  • Defoliation prior to GS 30 allowed crops to recover their yield to similar levels to uncut crops irrespective of the residual biomass. The only possible exception was EGA Gregory where grain yield was reduced by 13% when only 0.5 t/ha remained at GS30.
  • Defoliation after GS30 in both spring and winter cereals resulted in significant reductions in grain yield. The size of the yield penalty was related to residual biomass with more residual biomass resulting in lower yield penalties than those with more residual biomass
  • Defoliation after bud visible (BV) in canola was sensitive to residual biomass with crops with no yield reduction occurring if crops had > 3.5 t DM/ha remaining. Grain yield reductions were > 30% when crops had less than 2 t DM/ha at this time.

Figure 4 integrates results from several experiments where different timings and intensities of defoliation have been implemented. This suggests that there is a relationship between the time of lock-up and risk of a yield penalty with this increasing in canola after 20 July, irrespective of sowing date and variety. Yield reductions observed are larger in spring cultivars in more northerly locations than in winter varieties. After 20 July the capacity of the crop to recover grain yield seems to be greatly affected by the residual biomass remaining with levels greater than approx. 2.5 t/ha required at this time to allow the crop to fully recover. 

Bell Well 4

Figure 4. Relative grain yield (% of uncut) achieved from spring (a) and winter (b) canola defoliated at different times and intensities in experiments in central NSW. Spring cultivars are Hyola 575 (squares; red – Greenthorpe, orange – Coolah) and other spring canola (circles; dark red - Mullaley); Winter cultivars are Hyola 971 (circles; blue – Greenthorpe 2013, orange – Coolah)  and other winter cultivars (squares; orange – Coolah, red – Mullaley). Numbers next to each data point are residual biomass (t/ha).

Contact details

Lindsay Bell
CSIRO, Toowoomba
Ph: 0409 881 988
Email: Lindsay.Bell@csiro.au

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GRDC Project Code: CSP00160,