Long fallow: going the way of the dodo?
A respected authority from the United States has told Australian graingrowers that long-fallow dryland cropping is reaching a dead end, if not now, then soon. Greenhouse warming is just one reason.
Efficiency, cost and yield are three other good reasons. Jim Cook, professor of wheat research at Washington State University, was a keynote speaker at the Australasian Soil-borne Diseases Symposium at Lome in Victoria, supported by growers and the Federal Government through the GRDC.
He said the potential for soils to contribute to greenhouse warming is significantly lower for no-till than conventional tillage and planting. Covered soils offer a sink rather than a source of carbon dioxide.
Dr Cook acknowledged the greater threat of soil-borne diseases in no-till systems but offered a variety of management strategies.
These include planting in paired rows, exposing more soil to the sun (this may be a more viable strategy in higher-rainfall or cooler areas); sowing crops at an angle to old stubble rows so that less seed lands on top of old stubble; using high-quality seed with greater resistance; placing fertiliser below and to one side of seed at planting, giving plant roots access to better nutrition; occasional stubble burning; disturbing soil below the seeding depth.
Eliminating volunteer cereal and grass weeds two to three weeks before sowing eradicates a major source of infection.
He said, at the end of the day, cultural practices have reached a limit and the time has come to seriously work on root disease resistance in wheat and barley. Biotechnology will help provide the needed breakthroughs, he predicted.
For further discussion on fallowing and its alternatives, see our feature on changing practices for mallee soils p 14-15.
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