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Effect of grazing on cereal forage DM yields for whole crop silage

Joe Jacobs1 and Graeme Ward

Future Farming Systems Research, Department of Primary Industries, 78 Henna Street Warrnambool. VIC. 3280.
Email joe.jacobs@dpi.vic.gov.au

Abstract

Perennial ryegrass based pasture systems experience feed deficits during winter and summer. Winter cereal forage crops offer potential on dryland dairy farms, for both grazing and ensiling opportunities. A study was undertaken to evaluate the DM production potential of wheat and triticale for grazing and subsequent silage production. Two experiments were established using either wheat (cv. Wedgetail) or triticale (cv. Crackerjack). Grazing treatments were silage only (NG), harvested at GS 84, or grazed at either GS21, GS24, GS 30 or GS 32 and subsequently locked up and harvested for silage. For wheat, DM yields at grazing increased (P<0.001) as the growth stage progressed. By silage harvest (GS 84), the DM yield of NG wheat was higher (P<0.001) than all treatments except grazing at GS 24. For triticale, DM yields at GS 21 were lower (P<0.001) than for either the GS 30 or GS32 grazing treatments. Grazing at GS 32 resulted in higher (P<0.001) total DM yields than all other grazed treatments. At GS 84 for triticale, DM yield NG was higher (P<0.05) than all other treatments. Herbage nutritive values at grazing were highest (P<0.05) for earlier grazing treatments for both wheat and triticale with crude protein and metabolisable energy values above 30% and 13 MJ/kg DM for both cereals. By GS 84, values ranged from 7.7 – 10.9 % DM and 8 – 9.1 MJ/kg DM for crude protein and metabolisable energy. Results indicate that cereals can be used in dairy systems to provide feed for both grazing and ensiling. However, consideration needs to be given as to the area sown and impacts on feed supply across the farm.

Key Words

wheat, triticale, grazing, silage, DM yield

Introduction

To be competitive in the Australian dairy industry, farmers need to improve their efficiency of converting their farm business inputs into outputs, thus reducing the overall unit cost of production of milk and improving profitability. Sustainable improvements in profitability of southern Australian dairy farms can be achieved by increasing the amount of forage grown and consumed on-farm, combined with the strategic use of bought-in supplements to support milk production during periods of on-farm deficits in the supply of energy and protein. Existing production systems (ryegrass based pasture only) experience feed deficits in winter and summer and alternative strategies are needed to increase on-farm forage production, to even out the seasonal distribution of forage production and to maximize the use of the ryegrass pasture base (Chapman et al. 2006). Winter cereals offer the potential of a high yielding crop that can be grazed and then be cut for silage. The potential of using cereal crops for both winter grazing and silage in New Zealand was highlighted by de Ruiter et al. (2002). However, their potential to fit into dryland dairy systems in southern Australia is not known. Virgona et al. (2006) have shown that grazing with sheep for less than 19 days prior to the onset of stem elongation had no detrimental effect on final grain yield. The aim of these experiments was to determine the effect of grazing either winter wheat or triticale at different stages of growth on DM yield and nutritive value at grazing and for silage.

Methods

Site preparation and design

Experiments were conducted on a commercial dairy farm (DemoDAIRY) (38o 14’ S; 142o 55’E) in south west Victoria. The soil, a fine sandy clay loam is described as a brown chromosol (Isbell 1996) derived from quaternary basalt. In late March 2007, the experimental areas were sprayed with a mixture of Roundup Max at 3 L/ha (540 g/L glyphosate), Dicamba 500 mL/ha (500 g/L dicamba) and Le-Mat 100 mL/ha (290 g/L omethoate) to kill emerging weeds and reduce any existing population of red legged earth mite. Fourteen days after herbicide application (12 April), experimental sites were sown by direct drilling using a cross slot No Till machine with DAP applied at 100 kg/ha (18 kg N, 20 kg P) at sowing. Following sowing 500 kg/ha of 3&1 super potash (33 kg P, 63.5 kg K, 41 kg S) was broadcast over the experimental area.

Two experiments were established using either wheat (cv Wedgetail) or triticale (cv Crackerjack). Both cereals were sown at 100 kg/ha to achieve plant establishment densities of 190 to 210 plants /m2 for wheat and 130 to 150 plants/m2 for triticale. Randomised block designs were used for each experiment with four replicates of each grazing treatment. Grazing treatments were silage only (NG) (harvested at GS 84), or grazed with lactating dairy cows at either GS21, GS24, GS 30 or GS 32 and subsequently locked up and harvested for silage.

Measurements

Prior to grazing (wheat: GS 21 6 June, GS 24 19 June, GS 30 17 July, GS 32 14 August; triticale: GS 21 6 June, GS 24 19 June, GS 30 27 June, GS 32 17 July) and harvesting at GS 84 (wheat 6 November: triticale 24 October), 10 cuts of plant rows each side of a 50 cm rod were taken per plot and weighed to determine DM yield. Samples were bulked on a plot basis, sub sampled for DM content and nutritive characteristics. Forage samples were analysed by FEEDTEST, DPI Victoria, for crude protein (CP) (nitrogen concentration x 6.25), neutral detergent fibre (NDF) and dry matter digestibility (DMD). Values were estimated for all samples using near infrared spectroscopy (NIR). Metabolisable energy (ME) (MJ/kg DM) values were calculated from predicted DMD values using the formula:

ME = [0.164 (DMD% + EE) – 1.61],

where EE = Ether Extract (% of DM) assumed to be 2% for all types of fodder (AFIA 2002).

In addition, DM yields were taken after each grazing to determine residual DM yield. Statistical analyses were undertaken using ANOVA (GenStat Committee 2003).

Results

DM yield

For wheat, DM yields at grazing increased (P<0.001) as growth stage progressed (Table 1). At GS 84, the DM yield of NG was higher (P<0.001) than all treatments except grazing at GS 24. Total DM yields were lower (P<0.001) for the GS 21 treatment than all other treatments. The trends for triticale were similar with DM yields at grazing at GS 21 were lower (P<0.001) than for either the GS 30 or GS32 grazing treatments, whilst deferring grazing until GS 32 resulted in higher (P<0.001) DM yields than all other grazed treatments. At GS 84, NG was higher (P<0.05) than all other treatments, whilst total DM yields for NG were higher (P<0.05) than all treatments except GS 24.

Table 1. Dry matter yields (t DM/ha) of wheat and triticale grazed at different stages of growth, cut for silage and treatment totals

   

Grazing

Silage (GS 84)

Total

   

DM yield (t DM/ha)

DM yield (t DM/ha)

DM yield (t DM/ha)

         

Wheat

GS 21

0.48

12.17

12.65

 

GS 24

1.28

13.74

15.02

 

GS 30

2.67

12.71

15.38

 

GS 32

4.32

10.30

14.62

 

NG

 

14.69

14.69

LSD(P=0.05)

0.632

1.041

1.049

Triticale

GS 21

0.59

14.11

14.70

 

GS 24

1.31

14.92

16.22

 

GS 30

1.82

12.69

14.51

 

GS 32

3.36

10.79

14.15

 

NG

 

19.85

19.85

LSD(P=0.05)

0.752

4.746

4.570

Nutritive characteristics

The CP content of wheat was highest (P<0.05) when grazed at GS 21 and lowest (P<0.05) at the GS 32 grazing (Table 2). The ME content at grazing was lower (P<0.05) when grazed at GS 32 compared to all other treatments, whilst NDF content was higher (P<0.05) at this grazing stage. By GS 84 there were no differences in the ME or NDF content of all treatments but the CP content of the NG treatment was higher (P<0.05) than either the GS 21 or GS 30 grazing treatments.

For triticale, the CP content when grazed at GS 21 was higher (P<0.05) than for all other treatments, with values decreasing (P<0.05) at each respective grazing time. Metabolisable energy values were higher (P<0.05) for the GS 21 and GS 24 grazing times than for (Table 3) other treatments, whilst ME at GS 32 was lower (P<0.05) than for GS30. The NDF content of both GS 21 and GS 24 was lower (P<0.05) than the other grazing treatments. By GS 84 there was no treatment effect on either CP and ME, whilst the ungrazed (NG) treatment had a lower (P<0.05) NDF content than all grazed treatments.

Table 2. The crude protein (CP) (%DM), metabolisable energy (ME) (MJ/kg DM) and neutral detergent fibre (NDF) (%DM) of wheat at different grazing times and when cut for silage

 

Treatment

 
 

GS21

GS24

GS30

GS32

NG

LSD (P=0.05)

Grazing

           

CP

37.0

34.2

30.6

23.2

 

1.29

ME

13.6

13.6

13.3

10.5

 

0.33

NDF

37.4

36.3

37.9

54.4

 

1.92

             

Silage

           

CP

9.3

10.6

9.7

10.4

10.9

1.05

ME

8.9

9.0

9.0

8.9

9.1

0.28

NDF

53.8

52.2

53.0

53.3

51.5

1.78

Table 3. The crude protein (CP) (%DM, metabolisable energy (ME) (MJ/kg DM) and neutral detergent fibre (NDF) (%DM) of triticale at different grazing times and when cut for silage

 

Treatment

 
 

GS21

GS24

GS30

GS32

NG

LSD (P=0.05)

Grazing

           

CP

35.5

32.3

30.0

23.4

 

1.84

ME

13.5

13.5

12.8

12.0

 

0.43

NDF

37.2

37.0

42.5

44.1

 

2.28

             

Silage

           

CP

8.0

7.7

8.3

8.5

8.4

0.83

ME

8.3

8.3

8.0

8.3

8.6

0.46

NDF

56.0

57.0

58.7

57.5

52.5

2.81

Discussion

Apart from the lower total DM yields for the earliest grazing treatment (GS 21), it would appear that for wheat, grazing anytime from mid tillering (GS 24) to the commencement of stem elongation (GS 30) does not adversely affect DM yields. In contrast, for triticale only grazing during mid tillering (GS 24) resulted in comparable DM yields to the ungrazed (NG) treatment, with other grazing times resulting in significant DM yield reductions for both silage (5.7-9.1 t DM/ha) and total (5.1-5.7 t DM/ha) DM production. For both wheat and triticale, the residual DM present after grazing was considerably higher for the later grazing treatments (data not presented) indicating poor utilisation of available feed for grazing. The demand for grazeable feed of high nutritive value in early to mid winter is high at this time as it coincides with early lactation on dairy farms in south west Victoria. At this time, growth rates for perennial ryegrass are low (Jacobs et al. 1999), thus the provision of cereal crops as a forage grazing option provides greater flexibility into the system.

The nutritive value of both wheat and triticale at grazing was more than adequate to contribute to the diet of dairy cows in early lactation. In fact, the CP content was such that consideration needs to be given to managing excess N in the diet and subsequent energy cost incurred in its removal in urine. At GS 84 the nutritive value of both cereals could only be considered as of moderate value with ME values between 8 – 9 MJ/kg DM and CP content of 7.7 to 10.9 % DM. Such values will tend to limit the use of silages made from these crops in the diets of dairy cows to periods of late lactation or as dry cow feed. It is likely that the only time that silages with high NDF values such as found here could be used in early or mid lactation is to increase rumination, slow down the rate of feed passage through the animal and minimise milk fat depression, providing the amount fed does not lead to extensive substitution of feed of higher nutritive value (Stockdale et al. 1997). One option to improve the nutritive value of silage may be to harvest at an earlier stage of growth, although this is likely to significantly impact on DM yield at harvest.

Conclusion

Winter cereal crops can be used in dairy systems to provide forage for both grazing and ensiling. There are limitations with the use of cereals in that only one grazing event is available and thereafter to maximise DM yields crops need to be locked up for silage. Nutritive value of feed at grazing is high, whilst for ensiling the feed value is moderate at best. Given this limitation, consideration needs to be given as to the area sown to cereals and the impacts on feed supply across the farm.

Acknowledgements

The authors acknowledge the Victorian Government, Dairy Australia, WestVic Dairy, Gipps Dairy and Murray Dairy for providing financial assistance for this study. We also wish to thank DemoDAIRY for the use of land on their farm to undertake the experiment. The technical support of Stewart Burch, Troy Jenkin, Robyn Bush and Paul Moloney are also acknowledged.

References

AFIA (2002). Laboratory Methods Manual. Australian Fodder Industry Association, Melbourne, Australia.

Chapman DF, Jacobs JL, Ward GN, O’Brien GB, Kenny SN, Beca D, McKenzie FR (2006). Forage supply systems for dryland dairy farms in southern Australia. Proceedings of the New Zealand Grasslands Association. 68, 255 - 260.

de Ruiter JM, Hanson R, Hay AS, Armstrong KW, Harrison-Kirk RD (2002). Whole crop cereals for grazing and silage: balancing quality and quantity. Proceedings of the New Zealand Grassland Association, 64, 181-189.

GenStat Committee (2003). GenStat Release 7.1. (VSN International Ltd: Oxford).

Isbell RF (1996). The Australian Soil Classification (CSIRO Publishing, Melbourne).

Jacobs JL, McKenzie FR, Ward GN (1999). Changes in the botanical composition and nutritive characteristics of pasture, and nutrient selection by dairy cows grazing rainfed pastures in western Victoria. Australian Journal of Experimental Agriculture. 39, 419-28.

Stockdale CR, Dellow DW, Grainger C, Dalley D, Moate PJ (1997). Supplements for dairy production in Victoria. DRDC, Melbourne.

Virgona JM, Gummer FAJ, Angus JF (2006). Effects of grazing on wheat growth, yield, development, water use, and nitrogen use. Australian Journal of Agricultural Research. 57, 1307-1319.

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