Prospects for grass-clover swards in beef production systems: A computer simulation of the practical and economic implications

A mathematical model of herbage production and utilization on grass and grass-clover swards in the context of an 18-month beef system is described. Using the model the potential costs and benefits of replacing grass by grass-clover mixtures are examined. It is projected that gross margins per hectare will be higher on grass-clover swards receiving little or no fertilizer N than on grass swards receiving 300kg N ha⁻¹. The higher average profits from grass-clover systems must be set against a higher year-to-year variation in the financial returns. To some extent the financial risk associated with the more variable annual profits may be reduced by only allocating a proportion of the forage area to grass-clover and continuing to devote the rest of the area to fertilized grass swards.These conclusions, which are at variance with other studies, are influenced by three key assumptions within the model. First, dry-matter intakes by beef cattle are presumed to be about 10% higher on grass-clover than on grass swards. Secondly, the metabolizable energy value of clover is assumed to be 5% higher than grass. Thirdly, the model projects that the available forage is utilized more efficiently on grass-clover swards, due to the more uniform seasonal pattern of herbage production. If some or all of these assumptions are rejected, the economic advantage moves in favour of grass-based production systems. Since confirmation of these assumptions awaits experimental work, the findings of the model can be seen as little more than informed speculation.