While the longer-term trend has been towards a reduction in the dominance of cereals in
winter crop rotations, the role of pulses and oilseeds remains relatively minor. For the winter
crops, the role of canola and pulses has increased significantly over the past two decades, but
the overall ratio of broadleaf crops to cereals has still averaged less than 1:8 at the state level
in the ten years to 2003.
Given the role that legume pastures play in farming systems over much of the state, the role
of broadleaf crops in the entire rotation is certainly even lower. To the extent that most
pastures in the cropping zone are broadleaf pastures, the proportion of broadleaf species to
cereals in the rotation is likely to be considerably greater than the recent 15% of crops that are
sown to broadleaf crops. However, data on pasture area are notoriously unreliable, and it has
not been possible to obtain comparable data for pastures in rotation with crops.
An important issue is what level of cereals in a cropping rotation is “sustainable”. While there
is no precise rule, a ratio of cereals to broadleaf crops and pastures closer to 1:1 is likely to be
closer to a biologically sustainable rotation for much of NSW. Long-term research (Heenan
and Chan 1992) has shown that cropping rotations based on approximate equal components of
cereals and broadleaf species (including crops and pastures) are the most sustainable in a
biological sense in southern NSW. Within that overall 1:1 ratio, a ratio of broadleaf crops to
cereal crops of around 1:4 is considered appropriate for sustainable cropping systems, given
that 2-3 years of consecutive cereals can create disease problems and that broadleaf crops can
create disease problems if the same crop is grown within four years in the same paddock.
Because of the lack of direct information on rotations, it is difficult to take these generalities
too far towards precision. For example, a rotation that has only cereals and pastures may well
be sustainable, without any broadleaf crops. Similarly, in continuous cropping where there is
no pasture phase, one broadleaf for every four cereal crops will not be sustainable (Heenan
and Chan 1992). Therefore, these ratios are merely broad-based targets that provide a basis
for measuring improvements in overall sustainability of the production of winter crops in
NSW.
Economic factors also have an impact on the role of pastures and non-cereal crops in
profitable rotations. For example, Patton and Mullen (2001) found that in the Central West of
NSW, a pasture component of around four years was profitable for a wide range of wool and
wheat prices and a cereal cropping phase of 3-4 years. In the lower-rainfall areas, profitable
rotations tended to have higher components of pasture or non-cereal crops and lower
proportion of cereals. These proportions have been found to be relatively stable over a wide
range of relative prices for crops and livestock.