CARMAN, Man. – The proverbial silver lining in the saturated soil cloud is that at least most of the nitrogen will be there for next year’s crop. However, nitrogen is disappearing at a rapid rate as soil microbes devour nitrates in saturated fields.
With current soil temperatures, fields can easily lose 16 pounds of nitrogen per acre per day.
John Heard, a soil fertility specialist with Manitoba Agriculture, said the wet soil conditions of earlier this spring are not the same as the wet soil conditions now.
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“In cool spring conditions, with the soil at five degrees Celsius, we can expect to lose between two and four pounds of nitrogen per acre per day,” he said.
This denitrification process occurs because soil microbes use oxygen. Once a soil is saturated, the microbes consume all available oxygen within 24 hours and then set their sights on nitrate nitrogen. This is the nitrogen that farmers have applied as fertilizer and that has converted to the nitrate form. It is plant-accessible in this form, but that also makes it microbe -accessible.
“Microbial activity doubles for every 10 degree Celsius temperature increase,” Heard said.
“So back in the spring with the soil temperature at five degrees, the loss wasn’t too bad. When we got to 15 degrees Celsius, denitrification doubled, from a max of four pounds up to eight pounds.
“When we add another 10 degrees Celsius and we get a soil temperature of 25 degrees, which we have today (July 12), we get up to a loss of 16 lb. of nitrogen per acre per day. In areas with extreme heat, where soil temperatures hit 35 degrees Celsius, nitrogen loss can double again, and hit 30 lb. or more.”
Unusual conditions
Heard said it’s unusual in Western Canada to have saturated soil along with high heat. Once a crop is in the ground, he added, the plants are usually able to consume all the moisture that Mother Nature pours down.
Heard said a soil thermometer is handy during spring seeding, again in the fall when applying anhydrous ammonia and for monitoring winter wheat survival.
The soil thermometers used by soil scientists typically cost less than $50 and are available at farm input suppliers.
