Grains Research and Development

Date: 03.11.2014

Tighter fallow management gives wheat best chance

Author: Nicole Baxter

Photo of two men inspecting wheat

Graham McDonald (right) and his son James were surprised by the performance of their EGA Gregory wheat in 2013 after a late seasonal break and a dry July and August.

PHOTO: Nicole Baxter

Graham McDonald says wheat is the most profitable – but also the most variable – crop grown on the two blocks his family farms, one 16 kilometres north of and the other 30km north-west of Condobolin, central New South Wales. Seasonal variability means yields fluctuate wildly, from three tonnes per hectare on average down to 0.3t/ha, depending on the season.

To capture every available drop of rain and turn it into grain, Graham and his family place a high priority on summer weed control.

CSIRO’s Dr James Hunt says research carried out as part of the GRDC’s National Water Use Efficiency Initiative showed that up to 72 per cent of wheat yield in central NSW is a consequence of summer rainfall.

John Small, extension agronomist with the grower group Central West Farming Systems, says that failing to control summer weeds within two weeks of a rainfall event means losing valuable stores of moisture and nitrogen.

“For every millimetre of soil water transpired by summer weeds, the subsequent crop loses 0.7 kilograms of nitrogen, equivalent to 1.5kg/ha of urea at 100 per cent application efficiency,” he says. “That means losing 20mm of moisture through weeds is losing 28kg/ha of urea.”

For the McDonald family, knowing how much moisture and nitrogen they could potentially lose with poor fallow management has reinforced the need for timely summer weed control. Graham says preparation for cropping starts the year before, immediately after harvest, to control summer weeds. He and his family use two 30-metre, tractor-mounted boomsprays to control germinating weeds as early as possible, ideally within two weeks of any rain.

For the EGA Gregory wheat (pictured above in 2013), the season broke in early May, which meant sowing started two weeks later than ideal. Graham sowed the crop into moisture at 25kg/ha with 50kg/ha of monoammonium phosphate. While June was wet, with 100mm of rain recorded, July and August turned dry, and Graham says the crop appeared to “turn blue”, or die, because of a lack of moisture. A further 50mm fell in September, which Graham’s son James says saved the crop. When the EGA Gregory was harvested, Graham says he was pleasantly surprised by the results. After just 340mm of rain for 2013, less than the McDonalds’ mean annual rainfall of 425mm, the EGA Gregory wheat yielded 2.5t/ha.

“Wheat is a remarkable and resilient plant,” he says. “I’m astounded by how well it recovered because it really looked terrible before the September rain.”

The only disappointment in 2013 was low protein levels (9.5 to 10 per cent), which he hopes to have remedied in this year’s wheat by applying higher nitrogen rates at sowing and topdressing with urea as the crop developed.

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Mystery of regional yield variability solved 

GRDC Project Code CWFS0013, FLR00005

Region South, North