JUST when you thought it was safe to go out and spread your urea, along comes a precision agriculture symposium.
But you've got the latest and the greatest so what's the problem?
You might like to read a paper delivered by Harvey manufacturer Roesners, makers of the Marshall Multispread, at last week's Precision Agriculture research Symposium held in Perth.
In a matter-of-fact presentation, company director Matt Roesner unveiled a new side to fertiliser spreading.
It's a given that spinner-type fertiliser spreaders do not apply fertiliser in a perfectly even manner, influenced by a range of factors including wind, fertiliser properties, spreader set-up, pattern overlap and bout width (distance between the centre lines of successive spreader passes in the field).
There's a standard physical test, as a national certification procedure, to test the performance of fertiliser spreaders, but it doesn't take into account the factors that affect the response of the crop to nutrients contained in the fertiliser.
And it pays to know exactly what the correlation is between uneven distribution and yield losses.
In collaboration with CSIRO, Roesners is developing a computer-based tool to initially investigate the relationship between nitrogen fertiliser, bout width, soil quality and season type.
The tool was used this year to model wheat crop yield and economic return for different background soil N levels, a range of idealised spread patterns, along with different soil and season types.
According to Mr Roesner, the different scenarios demonstrated the influence of several factors on the partial net income (PNI) for nitrogen fertiliser applied to wheat, using idealised spread patterns.
"In many cases bout width has less impact on predicted PNI than soil quality or season type," he said.
"The effect of bout width is more noticeable with a low background N of 10kg/ha, than at a higher level of 50kg/Nha."
Mr Roesner said while the physical testing standard considered the performance of the spreader, it didn't take into account the factors that affect the response of the crop to nutrients contained in the fertiliser.
These factors included season and soil type and background soil nitrogen levels.
Economic factors (crop prices and fertiliser cost) also influenced optimal fertiliser application rate.
"Therefore the optimum bout width may not correspond to that at which the spreader is certified, according to physical tests," Mr Roesner said.
"In the sample case this year there was a noticeable PNI penalty at small bout widths, which are primarily the result of higher fuel and labour costs associated with increased driving at narrow bout widths."
Mr Roesner said that based on sensitivity analysis, the impact of wider bout widths, and consequently less even fertiliser application, is greatest when background N is low and when high levels of fertiliser are applied.
In these cases, poor distribution of fertiliser results in yield losses, and therefore results in an economic disadvantage.
"When background N is higher, the negative impact of poor distribution is reduced, reinforcing the message that knowing background soil N levels is valuable," he said.
"It is therefore important that farmers understand background soil N before making decisions on fertiliser application rate."
