Farmers have four Rs for proper nitrogen management: right product, right time, right place and right rate.
Following best management practices like the four Rs is the best way to increase nitrogen fertilizer efficiency, said Rigas Karamanos, agronomy manager with Viterra in Calgary.
“The farmer has to decide how the four Rs fit his or her environmental conditions,” said Karamanos.
The rule of thumb often used is the crop uses only 50 percent of the nitrogen fertilizer applied. It would be a mistake to think the rest of the fertilizer is wasted, said Blair McClinton, executive manager of the Saskatchewan Soil Conservation Association in Indian Head.
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“It doesn’t mean farmers are only getting 50 percent value from fertilizer.”
The plant competes with organisms in the soil for the nitrogen to help decompose organic matter from the previous year’s crop. Over time, that nitrogen is released back into the soil and is taken up by the crop.
“A lot of nitrogen is caught up in that. Over time, it releases,” said McClinton.
While work has been done on helping improve nitrogen use efficiency, improvements are often tiny, with only one or two percent efficiency increases, he said.
“It’s not straightforward what kind of changes are needed to improve nitrogen use efficiency. It’s more nibbling around the edges.”
McClinton estimates the actual nitrogen loss from leaching into the soil or denitrification may be only 10 to 15 percent.
On the Prairies, with its dry soils and relatively low levels of nitrogen applied with the crop, loss to leeching and denitrification is low.
Ross McKenzie, Alberta Agriculture’s agronomy research scientist in Lethbridge, agrees the 50 percent nitrogen use efficiency in a single year can vary widely between farms. McKenzie believes about 60 percent of the nitrogen fertilizer is used in a single year, but it can be as high as 80 percent with ideal conditions.
Because it’s estimated only 60 percent of the nitrogen fertilizer is used, it doesn’t mean the other 40 percent is lost forever.
“It’s not really lost, it’s just tied up and over time it will be released again,” said McKenzie.
“Maybe it’s not as bad as what people think.”
It’s different when some of the four Rs aren’t applied and the wrong fertilizer is used at the wrong time.
McKenzie said a lot of nitrogen is lost if it’s broadcast as urea when the temperature is hot or when it’s applied as liquid fertilizer in the fall.
“If not wisely applied, the losses can be quite significant. It comes down to the farmers’ awareness and what forms and when it’s applied,” he said.
“I would say in the last 20 years farmers are more astute on their use of nitrogen fertilizer. The majority use fertilizer very wisely.”
More than half of nitrogen fertilizer is applied through direct seeding, which has a good efficiency of uptake.
“It’s not all lost from the system unless it’s poorly managed.”
McKenzie said volatilization, or nitrogen lost as ammonia gas to the atmosphere, increases with increasing soil pH, soil carbonate content and the pH of the added fertilizer. These kinds of losses are greatest with urea and liquid nitrogen fertilizer. Losses are greatest when the soil temperature is greater than 5 C and the air temperature is greater than 10 C.
Losses are also greater in sandy soils than heavier textured soils. Nitrogen fertilizer can also be lost in water runoff from the fields. It’s not advised to apply fertilizer to frozen soils.
One of the biggest concerns for farmers is leaching, the movement of nitrate nitrogen out of the root zone because of excess water. Leaching can occur in early spring or late fall under excess moisture conditions.
“The fertilizer will sit there for next year’s crop unless it rains in September and there is a potential for leaching or denitrification,” said McKenzie.
In the past two years of dry weather, a little excess moisture when fertilizer is applied is a risk most farmers are willing to take, he said.
Most leaching can be prevented if the fertilizer is applied in the spring, close to the time of seeding.
Karamanos said scientists have been studying ways to minimize nitrogen loss since the 1960s. Using a stable isotope that could be tagged onto the fertilizer, research at the University of Saskatchewan showed about 50 percent of the fertilizer was used in the first year, 25 percent in the following year and about seven percent in the third year. Overall, the plant eventually used 82 to 83 percent of the tagged fertilizer.
Studies in the 1970s from the University of Alberta showed only about 20 percent nitrogen efficiency when it was broadcast on sandy soil.
“If you go back in the literature there’s some wonderful work done at the time,” he said.
“If someone is doing best management practices they have no reason to fear their fertilizer is being wasted.”
Denitrification: don’t let it happen to you
Denitrification, the enemy of farmers and the environment, happens when nitrate forms of nitrogen are converted to nitrogenous gases such as nitrogen (N2) and nitrous oxide, which are then lost to crops as they enter the atmosphere.
Fertilizer in the form of nitrate-nitrogen may be lost due to denitrification when soils are temporarily wet in late fall, early spring or after heavy rainfall. The microorganisms that convert nitrate to nitrogenous gas do their best work under high moisture or saturated soil conditions.
For this reason, nitrogen fertilizer should not be applied in the fall or spring, ahead of planting, to areas that are subject to saturated soil conditions ahead of planting or to low lying land subject to flooding.
Because of possible denitrification losses, it is generally recommended that fall applied nitrogen be banded in the ammonium form and applied as late as possible when the soil is cold, and organisms are slowed, so the nitrogen will remain in the ammonium form.
Denitrification losses do not occur as long as the fertilizer nitrogen is present in the ammonium form.
Recent research in Saskatchewan has shown there is greater potential for losses of nitrogen through denitrification under minimum and zero-till cropping conditions than when conventional tillage is practised because soil is moister and supports greater microorganism activity.
Source: Alberta Agriculture, Agriculture Canada, Viterra
