Tips for measuring nitrogen losses using dositubes

A protocol on how to use dositubes to measure nitrogen losses in cropland was developed by the University of Guelph, and has been used extensively by agronomists in Ontario. 


The method uses a gastec passive dosimeter tube (dositube) to measure NH3 losses.


“They’ve used this in Ontario for some time, and we have just de-veloped a protocol that growers can use,” said John Heard, Crop Nutrition Specialist at Manitoba Agriculture. 


“I target it towards agronomists to use first. (They can use it to) evaluate relative losses of ammonia from surface-applied urea, for example. Others have expanded to see if there are any losses from shallow-banded urea.” 


The original protocol for measuring ammonia losses on cropland called for measuring or estimating wind speed, so the actual losses in pounds of nitrogen per acre could be calculated. 


However, Heard has simplified the protocol, partially because Brandon researchers did not find the Guelph estimates worked in their prairie farmland measures.


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“I no longer suggest people frustrate themselves by measuring/estimating wind speed so they can determine actual loss in pounds of N per acre,” Heard said. 


“Just use the gauge in ppm (parts per million) NH3, to gauge relative losses.” 


The losses are to be gauged relative to high- and low-loss checks.


“You have a check area with no nitrogen applied, so that should continue to read about zero. And then you’ve got an area that I consider to be a high check, and that would be surface applied urea.”


To use a dositube, a blue recycling box or five gallon pail with six holes in the top and six holes in the side is needed. The holes allow air exchange. The pail is placed on the area to be measured. 


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“Put a rock on top so it doesn’t blow away. And under that you would put a stake with a dositube attached with an elastic. And then you would just measure accumulative ammonia over the next few days or weeks, or until you get about a half inch of rain.”


A half-inch of rain should be enough to take any surface nitrogen into the soil, Heard said. 


Each dositube costs about $7.


For more information, contact Katie Gibb at Phoenix Solutions: gibb.kt@gmail.com.


A poster that outlining the technique to use dositubes is available at: bit.ly/2qrI3LO.


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