There’s a surprising nugget of information in the latest North Dakota Crop and Pest Report about ammonia volatilization after shallow incorporation of urea.
“My colleagues in the soil fertility world have often assumed that shallow (inch or so) incorporation of urea was better than no incorporation at all,” Dave Franzen, North Dakota State University Extension soils specialist wrote. “A recent publication out of Quebec destroyed this assumption and found that even in a slightly acid soil, ammonia volatilization from urea was about four times more during the first 10 days after application when incorporated an inch deep, compared to not incorporating the urea at all (Rochette et al., Journal Environmental Quality, 2014).”
“This means that both surface and lightly tilled urea down to a depth of 2 inches should have a urease inhibitor (Agrotain and its NBPT containing brothers and sisters/Limus-NBPT+NPPT) to prevent ammonia volatility for about 10 days,” Franzen continued. “If urea is applied to the surface, it is better to leave it alone rather than incorporate it in a no-till/strip-till system. Conventional till systems should set the cultivator 3-4 inches deep.”