Knowing the ‘4Ls’ helps manage nitrogen

John Heard

When it comes to improving fertilizer application and utilization, growers are encouraged to focus on the 4Rs — the right source, right rate, right time, and right place.

Former Manitoba Ag soil fertility specialist John Heard won’t argue with that strategy but he would also like farmers to think about the ‘4Ls’ — lift-off, leftover, loitering and leakage — when managing nitrogen and getting the most bushels per pound from the nutrient.

At the recent Ontario Agricultural Conference, Heard threw his support fully behind the 4Rs but also emphasized the importance of understanding how and where nitrogen is lost. “That’s the 4Ls. That’s how how you trigger your 4R strategy,” he says.

Heard used ‘lift-off’ to describe the volatilization of surface or shallow-applied urea or UAN. Based on Ontario farmer utilization surveys, he feels growers have a good understanding of the impact of volatilization because one-third of the urea or UAN going down in the province is applied with some form of a urease inhibitor.

“That’s because they know what the risk is,” says Heard. “When you lay nitrogen on the surface, and if you don’t get rain, and if it’s a sandy, low organic matter soil, followed by drying and warm conditions, we can lose a lot of that nitrogen.”

Heard uses ‘leftover’ to describe the crop residue and how it’s important to ensure that microbes, which work to break down that residue, don’t chew up valuable nitrogen that’s intended for the new crop. “Depending on how you manage nitrogen, we can advantage one over the other,” he says.

“If you’re broadcasting and incorporating your nitrogen, you’re feeding the bugs — they’re first at the trough, and the crop is getting what’s left,” he explains. “I can switch the tables, leave that residue stranded on the surface, band my nitrogen below, and I’ve got a physical separation and [crop] roots are going to get that band. So there are ways to to fool Mother Nature.”

In this interview with RealAgriculture’s Bernard Tobin, Heard also shares how nitrogen can loiter when it’s applied too early and can leak — through leaching and denitrification — before the plant has an opportunity to take it up. Watch or listen to the full report below.

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