SOIL amelioration and nitrogen go hand in hand if the rest of the profile is balanced and yield potential is increased, said CSBP senior agronomist James Easton, as he discussed the results from the 2018 trials at the CSBP research and agronomy conference at Optus Stadium last week.
Mr Easton said CSBP has conducted a lot of trials over the past 10 years to see what could be done to get better results from the nitrogen they were using and what they could do to increase nitrogen use efficiencies.
In the past few years they have focused closely on soil amelioration, in particular deep ripping, at a number of sites to find out the effects of amelioration on N (nitrogen) requirements.
"We have asked the questions, can we cut back on N because the soil is better at sourcing N after amelioration?" Mr Easton said.
"The roots are getting down into the profile after deep ripping and capturing all of the nitrogen so should we be maintaining our inputs?
"We are growing more crops so should we be putting on a lot more N after amelioration?"
Mr Easton said in the longer term there was no doubt for growing bigger yields, more nitrogen was needed just to replace what had been taken out.
"At some point the yield needs to make up for the nitrogen it's pulling out," he said.
"Whether it be gypsum, lime or deep ripping, we need to find ways to replace the N source."
CSBP trials have been taken over five sites which helped to form the 2018 trial data.
Bunjil
The trial site at Bunjil had a lot of compaction down the profile, with the ripper down to 45 centimetres.
Mr Easton said the ripper was highly effective at breaking up the compaction layer.
"This was an emission trial," he said.
"So we were looking at the effects of not only deep ripping on nitrogen but also phosphorus and potassium requirements."
In year one, 2017, the trial cut back the applied N and in some plots applied no N after deep ripping.
"The trial showed we were getting as much yield with zero N as what we got with higher rates of N," he said.
"But we are only talking 2 to 2.5 tonnes per hectare yields so we don't need a lot of N anyway for those low yields."
This same trial was cropped again last year with higher rates of N up to 70 kilograms a hectare.
"We saw similar responses from nitrogen with ripping and non ripping," Mr Easton said.
"In this scenario, with much higher yields getting up to 4t/ha it has paid to maintain the nitrogen inputs.
"We have removed 15 kilograms of nitrogen from the soil with deep ripping which needs to be made up otherwise we will run down our organic reserve."
Binnu
The Binnu trial was completed in 2015 but showed similar results to the Bunjil trial.
There were big responses to deep ripping with close to 1t/ha increase in yield.
Mr Easton said if the yield potential was only 2t/ha, then no N might have done the job but it certainly pays to keep those N inputs up.
"The interesting thing about Binnu is it was quite acidic and it was a dry finish so we had a great response to deep ripping," he said.
Tammin
A good response to deep ripping at the Tammin trial site resulted in a 0.5t/ha increase in yield.
"We only had a 2.4t/ha yield potential, so we don't need a lot of N but again it does pay to maintain the N inputs," Mr Easton said.
"Although it's possibly potassium limited the response to N at this trial as it was deficient in other nutrients which are essential to seeing N results."
Merredin
In the previous three trials it was necessary to maintain N applications after deep ripping but this wasn't the case in all sites.
At the Merredin trial site CSBP recorded no response to N and deep ripping.
"Despite a lot of compaction there was limited response from deep ripping but it wasn't significant, about 200kg/ha," Mr Easton said.
"This trial had 2t/ha of lime and 0.5t/ha of gypsum prior to ripping and 5-10 tonnes of lime over the past 10 years.
"The problem was none of the lime had made its way down to the subsoil so the PH wasn't great."
Mr Easton reiterated his point of a healthy soil, saying the aluminium and potassium levels weren't great either which he thought limited the response of deep ripping and Nitrogen in this particular trial.
"Just because we are ameliorating the soils, we may not need to be feeding our crops, there may be other constraints not being addressed," he said.
"We need to see what the subsoil tests tell us, like is there enough potassium?"
Jerramungup
At the Jerramungup trial there was a lot of compaction down the profile.
Mr Easton said he was impressed with yields at 3t/ha which was an outstanding result considering the trial was re-sown at the end of June due to wind erosion.
"This trial had a great response to deep ripping but not a great response to N," Mr Easton said.
"Because it was coming out of rotation with lupins, which produced enough N in the soil, the crop didn't require that N for a yield increase.
"More N would have increased the protein for sure, which it did, but we need to look at the demand and supply of the soil."
Mr Easton said they got these big responses from deep ripping, particularly when there is N already present in the soil.
He said looking at the soil tests across the sites, the results are predictable.
"Sometimes you thought you wouldn't get any response when you look at the balance in the soil," he said.
"I think in the lower yielding years, where the potential isn't great, people could maybe cut back on their nitrogen.
"But the better yielding seasons it pays to maintain your inputs and over time increase them."
Mr Easton said the problem wasn't only in compaction when looking at N efficiency.
"If your primary subsoil constraint isn't compaction then you need to fix that primary constraint first before you look at deep ripping," he said.
"People need to be careful about ripping every paddock because the key to that is having a full soil test profile to see where you are getting responses with pH and balances.
"It comes down what your biggest constraint is and if the aluminium or pH isn't right down the profile then you wont get the responses of deep ripping on your N."
Mr Easton then highlighted the importance of other nutrients.
"Potassium is a big one out there at the moment and the big question is whether we are putting enough on," he said.
"If you are going to be limited by potassium or some other nutrient, you aren't going to get the returns or the nitrogen use efficiency from the nitrogen you put on."
Mr Easton left the group with a message that "N is the big lever but we can't lose sight of the importance of having enough of everything else in place".