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MANAGING ANNUAL PASTURES TO BENEFIT GRAIN AND OUT-OF-SEASON LAMB PRODUCTION

M.C. Crawford1, A.L. Avery1 and M.P. McCarthy2

1Agriculture Victoria, Department of Natural Resources and Environment, Rutherglen, Vic, 3685
2
Catchment and Agricultural Services, Department of Natural Resources and Environment, Bendigo, Vic, 3550

Abstract

A priority of the meat industry is the consistent supply of lambs through increased production in periods of traditional low supply. A priority of the grains industry is the production of high quality grain. In Victoria, a new project has commenced to develop and promote systems that increase yields of quality lamb and grain from the cereal/livestock zone while enhancing the soil resource. One such system uses the annual legume, subterranean clover, as a pure pasture in order to increase nitrogen accretion. Results of preliminary simulations using GrassGro for three sites in Victoria show the potential for increased pasture and silage production through this system.

Key words: Pastures, silage, GrassGro, prime lambs, crops.

The valuable role of pastures in broadacre cropping rotations in south-eastern Australia has long been recognised. In recent years, there has been an increased understanding of the potential value of enhanced pasture management to improve the quality and yield of grain crops, especially through nitrogen fixation and disease reduction. However, at the same time, it is generally acknowledged that the quality of many pastures in cropping rotations is poor. Any attempt to improve the quality of pastures in the cereal/livestock zone must recognise the role they play in an integrated system of grain and prime lamb production (Fig. 1). Closer examination of this system reveals that through increased inputs and better management, synergistic benefits to both the grain and prime lamb enterprises can be obtained.

In this paper, simulations using GrassGro (Horizon Technology, Roseville, NSW) are presented that illust-rate the potential production from a high-input annual legume pasture.

Materials and methods

GrassGro is a computer program which seeks to predict pasture growth and decay and associated performance of grazing animals (2). GrassGro was used to simulate the growth of an annual grass/ subterranean clover pasture and a pure subclover pasture (ie. winter cleaned) for three locations in Victoria's cereal/live-stock zone; namely Horsham, Bendigo and Rutherglen. The annual grass/subclover simulations represented a typical annual pasture on a low fertility soil with small reserves of subclover seed (50 kg/ha). The pure subclover simulation represented a situation where fertility was not limiting and the seed bank was greater (400 kg/ha). The simulations were run using historical meteorological data for each location, on soil types common-ly found in each area.

Results

The maximum amounts of green available herbage for each location are presented in Table 1. The 50 % per-centile value represents the maximum amount of green herbage that would be available in five years out of ten. At all sites, a high-input pure subclover pasture would yield more herbage than a low fertility annual grass and subclover pasture, if it were to be cut for silage or hay at the time of maximum green available herbage. The 30 % and 70 % percentile values indicate the range of yields that could be expected. Using the rule of thumb of Peoples et al. (3) that 25 kg of N is fixed for each tonne of legume herbage produced, a good subclover pasture can fix 50-100 kg N/ha more than a typical annual pasture in five years out of ten. This extra nitrogen is potentially available to the following crop.

Discussion and conclusions

The meat industry requires a greater consistency of supply of high quality lambs. To finish lambs out-of-season, there must be a feed supply. Options for provid-ing an out-of-season feed supply include a feed supply that is actively growing over this period (ie. lucerne or a summer active grass), a feed supply that is dead but still of high quality (ie. dead residues of annual legumes), or a feed supply that has been conserved and can be utilised when needed (ie. silage, hay, or grain, or a combination of these). A realistic option that potentially benefits the following grain crop is an annual legume pasture, conserved as silage to provide high quality feed to finish lambs out-of-season. The challenge is to manage the annual legume pasture to consistently achieve its yield potential, while maximising benefits to the following grain crop. Through improved management of the pasture, the following grain crop benefits from greater nitrogen fixation, improved soil structure, and better disease and weed control.

These simulations show the potential yield advantage associated with high-input pure subclover pasture. However, the cost of these inputs needs to be recouped through additional grain yield and quality and through more high value prime lambs. The degree of risk associated with a high-input annual legume pasture also needs to be considered. The benefits of improved past-ure management to the following crop have been demonstrated by others (1) and now the challenge is to effectively integrate this improved pasture management with prime lamb production. This challenge is taken up in a new project funded by the Government of Victoria through its Agriculture and Food Initiative, that aims to develop components of the grains/prime lamb product-ion system to increase the supply of quality meat and grain. Through this project, detailed investigations of the interactions of winter cleaning and fodder conservat-ion will be investigated and their benefits to the grain and meat enterprises on the farm evaluated.

References

(1) Latta, R.A. and Carter, E.D. 1996. Proc. 8th Aust. Agron. Conf., Toowoomba. pp. 365-368.

(2) Moore, A.D., Donnelly, J.R. and Freer, M. 1997. Agric. Syst. 55, 535-582.

(3) Peoples, M., Gault, R., Angus, J., Bowman, A., Brockwell, J., Kemp, D., McCallum, M., Paul, J., Quigley, P., Rifkin, P., Scammell, G. and Wolfe, E. 1997. Proc. 12th Ann. Conf. Grassld Soc. NSW., Orange. pp. 20-29.

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