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 the recent 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.
Mr Al-Awad said work since 1998 had identified differences in canola genotypes and the way they react to ammonium toxicity.
He hoped his work would define a critical level of ammonium concentration in relation to canola genotypes.
