The questions, how much nitrogen was applied and how much is available don’t have the same answer.
Seven crops into a long-term study on nutrient management at the National Centre for Livestock and the Environment, researchers have found that current provincial guidelines for estimating nitrogen availability may not reflect reality when it comes using solid manures.
“Based on the two solid manure sources we worked with, which is solid dairy manure and solid pig manure, we see that the nitrogen is coming out much more slowly than standard provincial recommendations would have predicted,” said Don Flaten of the University of Manitoba. “The provincial recommendations predict that most of the nitrogen that comes out of that solid manure is going to come out in those initial years, and then less and less and less each year.”
But that doesn’t appear to be the case, said Flaten.
Provincial guidelines estimate all types of manures release 25 per cent of their organic nitrogen during their first year, and release less nitrogen in subsequent seasons.
The first six years of data collected at the expansive test site just south of St. Norbert show that despite high rates of annual application, the cumulative efficiency of all solid manure present left available nitrogen at only five to seven per cent.
“But we know one thing for sure, that the organic nitrogen that is in the solid manure sources is not coming out anywhere near the rates or even the same pattern that the traditional recommendations assume is taking place,” said the researcher. “In fact, we’re finding it’s the other way around — that there is sort of a lag phase while the decomposition is just getting started, then finally, it starts to come out later on… it takes awhile to rev up. So rather than depreciating over time, the nitrogen value seems to appreciate over time.”
The findings mean that some farmers who think they have enough nitrogen, may actually be deficient.
“In some cases we may be running the crop short of nitrogen, because we’re assuming more nitrogen is coming out of those manures than actually shows up,” Flaten said, adding that nitrogen loss is also a concern as nutrients build up before being released.
“If you take a look at a lot of the nitrate that’s in groundwater, it’s old nitrate that was released when the land was first broken out of native prairie and there was such an incredible amount of mineralization and release of nitrogen in those freshly broken soils that a lot of it was lost,” he said. “And I think that we have to make sure that we don’t — with let’s say our solid manures — create the same sort of scenario, where you have a lot more nitrogen being released than you require.”
But that doesn’t mean it’s time to change provincial guidelines, at least not quite yet.
“We have to be somewhat cautious in drawing conclusions about changing those recommendations because we’ve only got two types of solid manure (in this study),” he said, adding that other researchers at the University of Manitoba are also looking at the properties of other types of manures in relation to the release of nitrogen.
All of that research would need to be compiled, assessed and compared before new recommendations could even be considered, he said. Additional studies could be required as well.
In the meantime, Flaten urges producers to have their soils tested.
“I think soil testing is the key step in all of these nutrient management systems, whether you’re working with synthetic fertilizers, or liquid manures or solid manures, — measure the amount of nutrient that you have, before you start applying a whole bunch more,” he said.