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How long can NBPT-Treated Urea Remain on the Soil Surface without Loss? (06/08/17)

Although a few areas of the state have received over ½ inch of rainfall in one event, many other areas have not.

How long can NBPT-Treated Urea Remain on the Soil Surface without Loss?

Although a few areas of the state have received over ½ inch of rainfall in one event, many other areas have not. If urea is surface applied, and a proper rate of NBPT was included in the application, urease activity and resulting ammonia volatilization is nearly zero for about 10 days. After the 10 day period, ammonia volatilization slowly increases, with subsequent volatilization being roughly exponential. If the soil is perfectly dry, ammonia volatilization is slow. A little rain (1/10 inch for example) would result in more loss, as ammonia partitions into the water as dissolved ammonia and is whisked away from the field with evaporation. Ammonia volatilization rate is low in soils with pH less than 7, and much greater in soils with pH greater than 7. Higher surface residue content also increases ammonia volatilization, because soil urease concentration is much greater in residue than in bare soil. It takes about ½ inch of rainfall in one event to move urea down into the soil enough to adequately protect the urea.

Dave Franzen

NDSU Extension Soil Specialist

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