When should growers apply nitrogen during the growing season to help their soybean crop optimize yield?
That’s a question Ontario Ministry of Agriculture, Food and Rural Affairs soybean specialist Horst Bohner tackles in this 2021 Ontario Diagnostic Days video report.
Bohner kicks off the discussion with help from Aaron Stevanus, agronomist and Mosaic technical sales manager. For Stevanus, a key point of emphasis is the important role nitrogen plays in helping no-till soybeans flourish in higher levels of residue produced by higher-yielding corn crops.
Stevanus says growers should certainly consider early-season nitrogen to jump start nodulation and help soil microbes break down corn stalks. However, yield returns on early nitrogen can be disappointing. Bohner notes that his research trials have typically shown a one to two-bushel yield response. He’s comfortable with a 50 lb/ac early-season application, but above that it’s difficult to make it pay.
When it comes to effective nodulation, both Bohner and Stevanus also stress the need for other nutrients, including adequate levels of magnesium and potassium. (Story continues after the video.)
Bohner then shifts focus to mid-season nitrogen application with help from NK Seeds agronomist Matt Rundle who notes the prevalence of poor mid-summer soybean stands in 2021 after the crop struggled through dry early conditions followed by late June rains and a wet July.
Rundle shares research that indicates one bushel of soybeans requires five lbs of nitrogen — that’s 250 lbs for a 50-bushel crop. Growers can count on nodulation to produce just over half of the plant’s nitrogen needs but in a season like 2021, when many soybean fields suffered through wet feet, growers need to resist applying too much of the nutrient. Again, research on mid-season applied nitrogen indicates a yield bump of only one to two bushels per acre.
Patience will be rewarded, says Bohner, noting that the crop does have the ability to bounce back when soils dry out and conditions improve. He adds that over-applying nitrogen mid-season can also be costly from a disease perspective when humid, wet conditions also promote white mould development.
“If we have patience, the beans will come out of it and, at the end of the day, you’ll be further along to leave them alone and not try to feed a significant amount of nitrogen at this stage,” says Bohner.