In most southern growing areas, summer rainfall has been more variable than the previous three years, soil moisture levels remain good and the 2023 winter crop season is shaping up well.
However, IPF technical agronomist Lee Menhenett says several seasons of high nutrient removal mean nitrogen levels are low in parts and tailored nitrogen strategies that maximise nitrogen use efficiency will be needed to optimise grain yields and returns.
He sees green urea as a good option particularly in the face of possibly patchier rainfall this season.
“Legacy soil moisture levels are generally good, and farmers who have been able to control summer weeds are placed well to have a good winter crop,” Mr Menhenett said.
“However, less reliable rain fronts mean it’s important to be organised when it comes to nitrogen programs, and green urea offers timing and operational benefits by expanding the spreading window and minimising volatilisation losses.”
When broadcast on the soil surface, both liquid or dry urea or urea-containing products or blends can be susceptible to ammonia (NH3) loss.
Studies show loss of top-dressed urea in southern Australia can be as high as 23% with green urea reducing those losses by more than 80% (Turner et al, 2010).
Green Urea NV is a urea-based product that is treated with N-(n-Butyl)-thiophosphoric triamide (NBPT) to inhibit the activity of the urease enzyme for a period of up to 14 days. During that period the losses of N as NH3 from the surface applied urea are significantly reduced and N is still present for the next rainfall event.
“Urea losses can occur for two weeks from the day it hits the ground, so there are a number of factors to consider when planning N application,” Mr Menhenett said.
“Firstly, if there is a reasonable rain front forecast, spreading may have to start three or four days in advance of that front to get over the required area.
“If the front doesn’t deliver the expected amount of rain, urea can be exposed to favourable loss conditions for a period of time. Usually in the days leading into a rain system wind speed increases with a negative influence on the spread pattern, which can drive increased gaseous losses.”
Mr Menhenett said the flexibility offered by green urea provides growers with confidence that if rain is late or less than anticipated, the nitrogen will be held in the system for longer and volatilisation losses minimised.
The cost of N losses on highly N-responsive situations will be more than just the value of the N application. If grain yield is compromised, which is highly possible on low N soils, the costs will be even greater.
When considering products that can reduce volatilisation, the potential return on investment is key.
“This year, with the system drying out, there’s value in having green urea on hand for when you need to top-dress but there is uncertainty around the timing and amount of rain,” Mr Menhenett said.
“As growers and agronomists we put a lot of planning into minimising volatilisation of things like trifluralin but can get complacent around more expensive inputs like urea and nitrogen.
“These are the inputs that could make the difference.”
Mr Menhenett said all farming systems should aim to maximise nutrient use efficiency.
“When choosing the most appropriate product, consideration should be given to the rate of application, the frequency of application, the timing of the application, the economic objectives, and environmental consequences.”
