History sheds revealing light on crop sequencing

Forty years of crop sequencing trials have recently been collated by the Department of Agriculture and Food WA (DAFWA), giving Western Australian grain growers real insights into the rotational benefits of break crops.

Representing more than 160 crop sequence experiments, the results were presented by DAFWA’s Mark Seymour at the Grains Research and Development Corporation (GRDC) supported 2009 WA Agribusiness Crop Updates.

Mr Seymour said the database not only revealed the benefits of break crops, but also shed light on the impact of changes to crop management over the years.

The data clearly demonstrates that continuous wheat was rarely as productive or economically viable as rotations that included either a pasture or break crop, regardless of how much nitrogen fertiliser was applied.

It also points to the difficulty of achieving yields higher than 2.5t/ha when wheat is sown after wheat. Overall, wheat sown after lupin out yielded wheat sown after wheat.

Since 1990 both the yield of wheat on wheat and the likelihood of a response to lupin in the following year have increased at all levels of applied nitrogen.

This corresponds with an era of more effective herbicide use and rotations that have shifted to more continuous cropping. Trials in this era were more likely to be sown with no-till machinery.

Narrow leafed lupin has been the most widely examined break crop species.

According to Mr Seymour, a lupin crop frequently provides a break from
Take-all, which severely limits wheat yields, or from high levels of annual ryegrass or brome grass. Other crops, such as field peas or canola, can also provide that essential break.

A detailed report summarising some of this extensive database is being prepared as part of the GRDC’s project “Increasing the Profitability of Cropping Systems in Western Australia using Lupins, Oats, Oilseeds and Pulses.”

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