Banding better in potash trial

Haidee VandenbergheCountryman

Applying muriate potash by variable rate rather than a blanket application can save growers about $10 a hectare, according to the results of a trial unveiled at the Facey Group's annual trials presentation.

With funding from the GRDC, Tincurrin Rural Services agronomist Clinton Mullan conducted and hosted the trial at his Dudinin farm.

The trial looked at two things - the most efficient way to apply potash and whether the radiometrics potassium map correlated to soil tests and yield data.

Mr Mullan said 300ha of the farm were surveyed by Precision Agronomics, using EM38 and radiometrics surveying.

"I looked at using the radiometric potassium map to see if we can use that to generate prescription maps for variable rate potassium applications," he said.

"Potassium is one of the more predominant nutrients which are lacking in a lot of our soil types and it's also one of the more expensive ones.

"The whole idea of doing this trial work is to ground truth - to make sure there are some gains in doing it."

With that in mind, Mr Mullan wanted to see whether the cost effectiveness of variable rate application meant you got your money back quickly.

In the second week of June, the 70ha trial site was sown with wheat variety EGA 2248, with plant counts at four weeks and plant tests at six weeks post sowing.

Potash was applied at 20kg and 40kg banded and at 40kg and 80kg spread. "We looked at spreading the potash and also banding the potash with the air seeder," Mr Mullan said.

"We've got the nil treatment, which is the control, and then two rates of banded potash versus two rates of spread.

"We also ground truthed that zone in April through CSBP soil testing, just to establish what the radiometrics map said was low was also low in the paddock."

The results showed the most efficient way to apply potassium was through banding.

"That surprised me a little bit," Mr Mullan said. "I expected the spread potash would be as good given the season we had with the good spring rainfall.

"The response obviously declined significantly in the higher radiometrics potassium zone, which you would expect."

Although there were no significant differences, the results showed distinct trends and allowed Mr Mullan to run some economics on the variable rate versus non-variable rate.

"Generally speaking, if you were able to band the optimum rate of muriated potash in this situation you would be talking about $10/ha difference … by variable rating versus broadacre blanket operation," he said. "That's just the result less the cost of the potash."

But despite the trial revealing the potential savings of variable rating potash, Mr Mullan said there were still some significant barriers for farmers wanting to employ the technology.

"The cost of machinery setup is one of the big ones and I think the other main barrier is just understanding the technology and how to use it," he said.

"At the moment, for us to variable rate potash across a whole program, machinery is the stumbling block.

"We would have to invest in some machinery to be able to do that.

"We've got spreading capacity to variable rate spread potash and lime gypsum. The ideal aim is to be able to do (variable rate potassium) down the track."

Mr Mullan said he would like to expand on the 2011 trial by collecting harvesting data this season.

"We'll follow what happens with the higher rates that were spread last year and see what it does to this year's crop to see if we pick up that gain in the following season," he said. "That will help build the picture a bit more.

"The higher rate of 80kg muriated potash, you would expect that to hang around for a couple of years unless there are really leaching conditions."

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