Trials at Edillilie on South Australia's Eyre Peninsula have revealed that while forage and grain sorghum summer crops may not be profitable on their own in the southern cropping zone, they could prove to be a valuable rotation crop in high rainfall areas.

Peter Treloar, of the Edillilie Farming Systems Group, says the trial provided a break from in-crop winter chemical regimes and made control of ryegrass and wire-weed (hogweed) easier.

The trial, initiated mainly to ascertain the effect of a summer crop on moisture in the soil profile, involved planting 3ha to forage and grain sorghum on a paddock that had been grazed the previous winter. The paddock was prepared using the double knockdown of glyphosate and paraquat.

The crops were not sown until the soil temperature started to reach 16°C by 9am, which finally happened on October 22. The sorghum was sown at a rate of 4-5kg/ha, with 80kg/ha of MAP and extra sulphur.

Peter says sorghum roots only marginally penetrated the heavy clay to be found beneath the topsoil at Edillilie, unlike lucerne. It was hoped the summer crops would dry-out the profile of a soil prone to water-logging.

However, the crops did manage to extract some water. Only one inch of rain fell during the whole summer growing season at the trial site, but Peter says the crop performed well in the conditions. After it was slashed for pasture, it began re-growing.

Freight rates being what they are on the lower Eyre Peninsula, Peter doesn't believe the grain sorghum will be profitable on its own, but the trial strongly suggests that in rotation, cereal crops sown afterwards will experience less pressure from weeds. The group is looking forward to planting wheat and barley at the site to measure the affect the summer crop has had on yield and quality.

The Crop Doctor is GRDC Managing Director, Peter Reading.