Should pulse crop growers use starter nitrogen?
Pulse and soil specialists say it depends on the type of pulse crop, the weather and the level of nitrogen in the soil.
Ray McVicar, special crops specialist with Saskatchewan Agriculture, said producers are looking to reduce crop inputs, particularly this year, and decreasing nitrogen fertilizer on their pulse crops is one way to do it.
That’s because legumes, especially inoculated legumes, convert or “fix” atmospheric nitrogen to a form of nitrogen available for plant growth.
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“But each crop is different, so while it may be an opportunity to reduce nitrogen fertilizer, producers cannot make any assumptions,” McVicar said.
“Only a soil test will tell them if the reduction of nitrogen is good economics.”
Early boost
Because it can take three to four weeks for nitrogen-fixing nodules to become fully functional, some believe a little starter nitrogen can help the crop, said Fran Walley with the University of Saskatchewan’s soil science department.
“But, although starter nitrogen can increase early vegetative growth, this does not always result in increased yields. It will increase final yields if nitrogen fixation is not optimized – if, for example, there is an inoculant failure, a dry seed bed, or other conditions that contribute to poor nodulation.
“Some producers report consistent yield increases resulting from the use of starter N, but others have found no crop benefits. Research supports both sides of the argument.”
Walley said one reason for the confusion is that all pulses are not created equal.
Peas are excellent nodulators and fixers of nitrogen. There is little evidence to suggest that peas will benefit from starter nitrogen.
Dry beans, on the other hand, are generally regarded as the worst nitrogen fixer of all the prairie pulse crops.
Research by Steve Shirtliffe, also of the U of S plant sciences department, has shown that inoculated and uninoculated bean yields increase in response to nitrogen applications.
“We are still learning about beans,” Walley said.
“But we are beginning to suspect that some beans are better at fixing nitrogen than others. It may mean that some varieties should be treated more like a non-fixing crop, which includes fertilizing them with nitrogen.”
Environment is another factor, both the general conditions of the soil zones and the conditions in a particular year.
“Peas grown in the dry brown soil zone, for example, are not the same as peas grown in the moist black soil zone,” she said.
“So the starter N issue is not clear-cut. Growers need to evaluate their own situation and stay away from generalizations.
“If starter N is not being used, all producers must remember the plant will be relying on nitrogen fixation. So they must make sure they do a really good job with inoculation.”
McVicar said it is important to have the correct inoculant product for the crop grown.
“For example, inoculant products suitable for lentil and pea are not suitable for chickpea,” he said.
“Producers should also be reminded to inoculate only the amount of seed that can be planted right away, as the bacteria in inoculants do not live long when exposed to the elements.”
He said a soil test will tell producers if their field is at a critically low level of available nitrogen.
“It provides a basis for producers to decide whether or not the addition of starter nitrogen is correct for their field.”
Walley’s article When to Use Starter N on Pulses is in the spring 2000 issue of The Saskatchewan Pulse Grower.
