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The effect of dairy effluent on dry matter yields and nutritive characteristics of summer active regrowth forage crops

Joe Jacobs and Graeme Ward

Primary Industries Research Victoria, Department of Primary Industries,
Warrnambool, Vic 3280. joe.jacobs@dpi.vic.gov.au

Abstract

The effect of dairy effluent on the DM yields and nutritive characteristics of chicory (Chichorium intybus L. cv. Grouse), Hunter (Brassica campestris L. x Brassica napus L.), Winfred (Brassica napus L.), and Sweet Jumbo (Sorghum bicolour (L.) Moench x Sorghum Sudanese (Piper) Stapf.) was determined. Second pond dairy effluent was applied at rates of 0, 40, 80 or 100 mm with half the effluent applied 6-8 weeks after sowing and the other half immediately after the first grazing. All forages were grazed twice with DM yield and nutritive characteristics measured at each grazing. Effluent indicated high concentrations of potassium (437.7 kg/ML) and moderate levels of nitrogen (132.3 kg/ML). Total DM yields of all forages increased (P<0.05) with effluent application. Effluent application resulted in increases in crude protein (CP) content at the first grazing, whilst by the second grazing, only the application at the highest rate increased (P<0.05) CP compared to the control. The study indicated that effluent can increase the DM yield for a range of forage crops through the late spring and summer whilst improving the CP content. Increases in forage CP during this period may alleviate some of the need to purchase costly protein supplementary feeds for lactating dairy cows.

Key Words

Summer crops, dairy effluent, crude protein, nitrogen,

Introduction

Given the general inability of perennial ryegrass to provide adequate DM yield throughout the summer under dryland conditions in southern Australia, the use of forage summer crops will remain a component of such systems provided they remain cost effective in relation to purchased feeds. However, in many situations DM yields are variable. A recent study (Jacobs and Ward 2003) highlighted the potential of using dairy effluent for turnip crops to improve both DM yield and nutritive value. Summer regrowth forages may provide greater flexibility in terms of feed availability over summer. This study determined the value of using dairy effluent to improve DM yields and nutritive value of a range of summer regrowth forage crops.

Materials and methods

This trial was conducted on a commercial dairy farm (3814’ S; 14255’E) in southwest Victoria. On 10 November 2004 allocated plots (12 x 12 m) were sown to Hunter, Winfred, chicory or Sweet Jumbo at 4, 3, 5 and 8 kg/ha respectively. For each forage, effluent was applied at rates of 0, 40, 80 or 100 mm with each treatment replicated four times in a randomised block design. Half the effluent was applied 6-8 weeks after sowing, with the remainder immediately after the first grazing with all forages being grazed twice. Prior to each grazing, herbage DM on offer and nutritive characteristics were determined. Statistical analysis was undertaken using REML (GenStat Committee 2003).

Results

Effluent analysis indicated concentrations of potassium (437.7 kg/ML) and sodium (496.9 kg/ML) and moderate levels of nitrogen (132.3 kg/ML). Approximately 60% of total N was in an ammonium form. Effluent increased (P<0.05) DM yields at both grazings with total DM yields of all forages increasing (P<0.05) linearly with effluent application (Figure 1). Dry matter yield responses were 48, 52, 29 and 51 kg DM per mm applied effluent for chicory, Hunter, sweet jumbo and Winfred respectively. Application of effluent resulted in increases (P<0.05) in crude protein (CP) content at the first grazing, whilst by the second grazing, only the application at the highest rate increased (P<0.05) CP compared to the control (Figure 2). Metabolisable energy, neutral detergent fibre and water soluble carbohydrate contents were unaffected by effluent.

Discussion

Apart from recent studies (Jacobs and Ward 2003, 2006) there are no comparable data on the response of summer forage crops to dairy effluent in Australia or New Zealand. The DM responses in this study compare favourably with those from previous studies. The response of chicory was similar to that of the two brassica species. A potential advantage of using chicory is that unlike brassica crops it is not susceptible to insect damage. In addition, being a perennial species it can contribute feed throughout the year and minimise the need for further cultivation and resowing in autumn. Effluent improved DM yield, had little effect on ME and improved CP content. The data indicate that despite a higher DM yield from chicory, both brassica species produced more ME per ha where effluent was applied due to their higher ME density. Such data emphasises the value of brassicas to provide good yields of a high energy feed over summer. Increases in forage CP during the late spring and summer in dryland areas of Victoria are of particular importance as most other available home grown forages are low in CP at this time. The study indicates that effluent can increase the DM yield for a range of forage crops through the late spring and summer whilst improving the CP content. Increases in forage CP during this period may alleviate some of the need to purchase costly protein supplementary feeds for lactating dairy cows.

Figure 1. Effect of applied dairy effluent on the DM yield of chicory (dark shading), Hunter (clear), sweet Jumbo (diagonal lines) and Winfred (spotted). l.s.d 1.379

Figure 2. Effect of effluent (0 (dark shading), 40 (clear), 80 (diagonal lines), 100 (spotted) on crude protein (CP) of chicory, Hunter, sweet Jumbo and Winfred at the first (G1) and second grazing (G2). l.s.d G1 1.73; G2 3.59

Acknowledgements

The authors wish to acknowledge the financial contributions of Department of Primary Industries, WestVic Dairy, GippsDairy, MurrayDairy and Dairy Australia and DemoDAIRY.

References

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

Jacobs JL and Ward GN (2003). Effect of different rates of dairy effluent on turnip DM yields and nutritive characteristics. 11th Australian Agronomy Conference. Geelong Victoria.

Jacobs JL and Ward GN (2006). The effect of dairy effluent on turnip DM yield and nutritive characteristics. Australian Dairy Science Symposium, Mt Gambier.

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