Research shows there is a limit to how much nitrogen improves irrigated sunflower yields and content.
PHOTO: Clarisa Collis
New South Wales Department of Primary Industries (DPI) northern cropping systems leader Loretta Serafin has found that sunflower oil content can suffer from too much nitrogen.
This was the finding of trials at Breeza on the Liverpool Plains and across northern NSW, which examined the effects of different nitrogen rates and plant populations in the wet 2012-13 summer grains season and previous seasons.
Ms Serafin says the research showed that applying high rates of urea to sunflowers in waterlogged conditions caused a decline in the crop’s oil content.
“This has implications for growers in terms of decreasing the price per tonne and increasing expenditure on fertiliser inputs,” Ms Serafin says. The trials also showed the importance of nitrogen budgeting.
“In the 2012-13 season, there was no yield benefit from applying urea at rates of 50kg/ha, 100kg/ha, 150kg/ha and 200kg/ha. However, levels of plant-available nitrogen in the soil before starting the trials were quite high at 114kg/ha. As a result, there was no yield benefit from additional applications of nitrogen.”
She says another finding of the study was there was no significant yield difference between three different plant populations, including 36,000 plants/ha, 48,000 plants/ha and 56,000 plants/ha under irrigation in a wet season.
This result backs up earlier research by Dr John Thompson at Leeton, NSW, in the 1970s, Ms Serafin says. His work showed that different plant populations had no effect on sunflower seed oil content.
“The trials did, however, highlight the crop’s ability to compensate for variable plant populations by adjusting the number and weight of the seeds on sunflower heads, plus the size of the plant and its flower head,” she says.
Dr Thompson’s research also helped to determine optimum seeding rates for irrigated sunflower cropping, with populations between 50,000 and 80,000 plants/ha providing the highest yields in the late 1970s and 1980s.
Ms Serafin says preliminary trials at Breeza on the Liverpool Plains, also in saturated conditions during 2011-12, showed that there were no significant differences in the yield of four different sunflower varieties.
However, this trial showed that irrigating the crop at bud initiation increased yields by 1t/ha compared with delaying irrigation until early flowering.
“Maintaining adequate water supply until the crop reaches physical maturity has the potential to optimise yields based on research by C.L. Browne at Leeton, NSW, in the 1970s,” Ms Serafin says. “This work showed that irrigating the crop up to 22 days after mid-flowering increased yields up to 19 per cent.
“However, in our trials waterlogging played a role in both the 2011-12 and 2012-13 seasons, so the research is continuing under different seasonal conditions.”
Ms Serafin says too much water could be just as damaging as not enough water, with waterlogging for any longer than 24 hours reducing yields by up to 60 per cent.
“But changes in sunflower varieties, agronomic practices and farming systems mean the question is whether these results still hold true today,” Ms Serafin says.
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