If you’re looking for a quick and easy guide to choosing the right placement for your nitrogen application, there isn’t one. Neither is there a one-size-fits-all strategy for timing or rate. There are, however, clear guidelines on how to improve nitrogen efficiency while limiting environmental impact. University of Manitoba soil science professor Don Flaten explains.
When it comes to nitrogen applications, better agronomic efficiency generally results in better crop uptake and less nutrient loss. This, in turn, improves profitability and reduces environmental problems. But variable weather and labour shortages lead some growers to apply nitrogen in less-than-desirable conditions.
In general, though, the most efficient way to apply nitrogen fertilizer is banding as close as possible to the time when the crop will use the nitrogen, said Flaten. This cuts down on volatilization losses and also lowers the risk of ammonium being converted to nitrate and then leaching below the root zone or denitrifying into the atmosphere. This practice also cuts down on the amount of nitrogen used by microbes rather than the crop. Finally, it restricts the amount of nitrogen that gets stuck inside soil minerals in a phenomenon known as ammonium fixation.
“All of those losses are reduced if you can band the nitrogen under the soil surface as close as possible to crop uptake,” said Flaten.
Consider the caveats
There are always caveats to consider with nitrogen applications, though.
“A number of these loss mechanisms are more intense in wet conditions than in dry conditions,” said Flaten. “If you have dry weather in the short term or dry climate in the long term, your farm might not be as vulnerable to these losses as other farms.
“For example, we find that fall banding of fertilizer works remarkably well in a large part of the Canadian Prairie region, but it doesn’t work as well in wet years or wet regions of those same Prairie Provinces,” he added. “The benefits of a best management practice vary from situation to situation.”
Broadcasting has also been shown to work well, but only under the right conditions and in certain situations. Over the past few years, Flaten’s research team has been broadcasting nitrogen mid-season in high yielding spring wheat trials because they didn’t want to put on large amounts at seeding. Instead, they applied a portion mid-season and used a urease inhibitor called Agrotain to reduce volatilization losses.
“This split application worked very well for us in a recent trial in Manitoba,” he said.
But split applications in some other trials in other parts of the Prairies showed that if you have a dry period after a mid-season broadcast application, you can leave a lot of that nitrogen stranded at the surface where the crop can’t access it.
“Across eight field trials with spring wheat in 2016–2017, we had excellent results from mid-season split applications, but in some other researchers’ trials, that included work in Saskatchewan and Alberta, the mid-season applications were more risky,” said Flaten. “It is so important to take a look at several studies to get a comprehensive picture of what your risks and rewards are for these practices.”
There is, however, one option that Flaten would not recommend and that’s fall broadcasting.
“Fall broadcast nitrogen is by far the worst, most inefficient way of applying nitrogen fertilizer,” he said.
Sometimes labour shortages and consistently sub-optimal weather conditions make spring applications challenging. If this happens, Flaten says growers should refer to the 4Rs as set out by Fertilizer Canada.
The 4R Nutrient Stewardship is a framework for nutrient management that is scientifically proven to improve nutrient efficiency, and increase crop yields and profitability while minimizing losses to the environment. The framework uses scientific principles to guide the development of Right Source, Right Rate, Right Time, and Right Place practices for different cropping systems.
While what is “right” will vary with cropping systems, available fertilizer products and application technology, there is an underlying concept that the selected practice will balance out economic, environmental, and social considerations, explained Cassandra Cotton, vice president of sustainability at Fertilizer Canada.
“While improving efficiency and return on investment is an important aim of 4R in all cropping systems, practices also have been proven to reduce greenhouse gas emissions by 35 per cent,” said Cotton. “If implemented across Western Canada alone, this would reduce nitrous oxide emissions by two to three metric tons of CO2 annually.”
Occasionally, growers may need to break from their intended practices to accommodate unusual circumstances, such unfavourable weather, equipment limitations or product shortages. This is understandable. But growers who choose sub-optimal application timing need to invest extra effort in the other components of the 4Rs to make extra sure that they’re using the right source in the right place, said Flaten. Doing so doesn’t just benefit the environment and the wallet, but also public acceptance or agricultural practices.
“At the end of the day, farmers are increasingly facing pressure from the supply chain and the general public to demonstrate on-farm stewardship and the 4R program can provide them with an opportunity to meet those challenges,” Cotton concluded.