Research shows canola's sensitive side

19 Jun, 2017 01:40 PM
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University of Western Australia Postgraduate Showcase 2017 research presenters, Robertson Khataza, Shahin Uz Zaman, Karen Frick, Haiyan Liu, Lauren Blekkenhorst, Omar Al-Awad, UWA Institute of Agriculture's Industry Advisory Board chairman Dr Terry Enright, UWA Future Farm 2050 project leader Professor Graeme Martin, Nicola Bondonno and UWA Institute of Agriculture director Professor Kadambot Sidd
University of Western Australia Postgraduate Showcase 2017 research presenters, Robertson Khataza, Shahin Uz Zaman, Karen Frick, Haiyan Liu, Lauren Blekkenhorst, Omar Al-Awad, UWA Institute of Agriculture's Industry Advisory Board chairman Dr Terry Enright, UWA Future Farm 2050 project leader Professor Graeme Martin, Nicola Bondonno and UWA Institute of Agriculture director Professor Kadambot Sidd

UREA promotes growth in canola through the uptake of nitrogen, but too much of a good thing can be a bad thing, according to University of Western Australia (UWA) research.

One of the studies being undertaken at UWA’s Institute of Agriculture and previewed at last week’s Frontiers In Agriculture, Postgraduate Showcase 2017, is on the effects of ammonium toxicity on growth of canola genotypes.

Work with canola genotypes in Lancelin soils by Iraqi PhD student Omar Al-Awad, who has been studying in Australia for three and a half years, has reinforced findings of other research centres that some genotypes are more sensitive to ammonium toxicity than others.

His research so far has also indicated combining nitrogen sources of ammonium with nitrate, may have a better effect on plant growth and possibly avoid the effects of toxicity on growth.

Mr Al-Awad explained to a showcase audience of students, academics and agriculture industry representatives, that urea “was the most important nitrogen fertiliser in the world”.

It was very cheap to produce and transport and at 46 per cent nitrogen, a cost-effective method of delivering nitrogen in nutrient-depleted soils, Mr Al-Awad said.

Urea application benefited germinating canola by promoting leaf canopy growth to maximise water utilisation.

“Usage of urea for nitrogen in farming in Australia has increased during the past 20 years, however there is not always a good outcome,” he said.

Urea hydrolyses breaks down in a chemical reaction with water in soil to release ammonium which is taken up by plant roots.

“Ammonium toxicity (too much ammonium for the plant to use) is one of the most common soil problems in the world, and most crops have poor resistance to the toxicity which can affect plant growth,” Mr Al-Awad said.

“Ammonium has been shown to be remarkably toxic to canola.

“The problem is, it (toxicity) often goes undetected.”

Symptoms include chlorosis, a loss of normal green colouring or a yellowing of outer leaves on a plant, and leaf curl.

Ammonium toxicity can damage new leaves and roots as it accumulates in the plant cells and its effects are more pronounced in colder, wetter months when lower soil temperatures and damp soils slow normal nitrifying microbial activity.

Microbes in the soil convert ammonium to nitrate, a simple molecule that is the predominant form of nitrogen in soil and the easiest form for plants to take up through their roots and store in their leaves.

As was pointed out in a question and answer session at the end of Mr Al-Awad’s presentation, there is some evidence plants will take up nitrate first, in preference to ammonium, if both are available.

Mr Al-Awad said work since 1998 had identified there were differences in canola genotypes and the way they react to ammonium toxicity.

He said he hoped his on-going work – he is in Australia for another year and a half – would define a critical or “optimum” level of ammonium concentration in relation to canola genotypes, establish which genotypes are more resistant to ammonium toxicity and test ratios of ammonium to nitrate.

Experiments using eight rates of ammonium chloride application, five rates of calcium nitrate, and a nitrification inhibitor, on four replicates over 35 days measuring shoot and root weight, had indicated the best and worst performing concentrations.

“Ammonium at a rate of 15mg per kilogram of soil did not have an adverse effect on the growth of canola and was the optimum concentration,” Mr Al-Awad said.

At 60mg per kilogram canola showed signs of ammonium toxicity, he said.

Soil pH had started at 5.9 and became more acidic at 5.6 as higher concentrations of ammonium chloride were applied.

Nitrate application showed an opposite effect with shoot and root weights increasing, and acidity decreasing, at higher application rates of 60 and 40mg per kilogram of soil.

Subsequently experiments applying 15 and 60mgs of ammonium chloride per soil kilogram on known “toxicity sensitive” and “non-sensitive” canola genotypes had been conducted with shoot and root weights measured.

Growth of all genotypes in response to 15mg “was significant”, Mr Al-Awad said, with roughly double the response of 60mg, but figures he showed suggested growth was even more pronounced on toxicity sensitive genotypes.

He said his experiments had shown Brassica napus (canola) genotypes BN39 and BN48 could grow at relatively high concentrations of ammonium.

But further work was required, he said, and his future studies would concentrate on the impact of ammonium toxicity on canola oil yield.

A third experiment compared the effect of a toxic rate of 60mg of ammonium on the growth of two sensitive and two toxicity-resistant genotypes with the effect of varying ratios of percentages of ammonium and nitrate.

“The rates of 25pc ammonium with 75pc nitrate and 50-50 really were the best for growth,” Mr Al-Awad said.

The combined nitrogen sources at those rates promoted growth in both the “sensitive” and “non-sensitive” canola, he said, but further work was needed.

Field trials to confirm the experiment results and establish appropriate field application rates were also needed, he said.

Other postgraduate research on the tolerance variation of field peas to waterlogging at germination, the potential for wetting agents to improve soil moisture content and distribution and reduce run-off erosion, and genomic research on improving narrow-leafed lupin was also presented by students from UWA’s school of Agriculture and Environment.

Students from other faculties presented on research related to cardiovascular health benefits from eating apples and vegetables, the impact of income and price sensitivity on diets globally and the speed of adoption of new technology by farmers.

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The view of the PGA on this issue suggests that they also believe that the earth is flat. At
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And Rural Realist WAFF are even worse. Look at their call on single desk, GM, wool floor price