Nitrogen is essential and expensive. But a good portion of the nitrogen farmers apply to the soil doesn’t get where it’s intended to go. Before the product can get to the plant in a form the plant can use, valuable nitrogen is lost through volatilization (released from the soil into the atmosphere as a gas), leaching (driven down deep into the soil to be useful) and denitrification (converted to a gas underground and lost).
Nitrogen efficiency enhancers, or nitrogen stabilizers, can limit these losses.
N loss to volatilization
When nitrogen is applied as urea it starts to break down as soon as it’s applied to soil that’s not completely dry. When urea contacts moisture and an enzyme called urease, a reaction takes place and ammonium and carbon dioxide are created.
John Kruse, research agronomist with Koch Agronomic Service, says urease is a naturally occurring enzyme. “It’s very, very common,” Kruse says. “It’s on your skin, everywhere.”
The ammonium produced by urea’s reaction with the urease enzyme is a gas. When rain or application techniques move the urea down into the soil before the reaction takes place, losses are minimal. However, when the reaction happens on the soil surface ammonium gas is released into the air. This is volatilization — a major cause of nitrogen loss.
Kruse says, “It just gasses off, right into the atmosphere. The grower can lose a very significant portion of his investment.” Kruse says losses can be 30 to 40 per cent or higher. “It can just simply turn into ammonia gas and volatilize away. Nobody wants to pay for 10 pallets of fertilizer, but the crop only sees six pounds.”
While the days of applying nitrogen on the surface have, for the most part, passed by, Kruse says if farmers are applying fertilizer just under the soil surface, scratching it in, “there’s still a great potential for nitrogen loss.”
Kruse says the solution is to “really bury it,” or protect the nitrogen with a nitrogen efficiency enhancer.
N loss to leaching
Kruse suggests thinking of soils and nitrates like magnets — opposite charges attract. Ammonium in the soil has a positive charge. “Soils are typically negatively charged,” Kruse says. The attraction allows the plants to use the nitrogen.
Having positively charged ammonium in your soil isn’t a guarantee. Kruse says, “There are other naturally occurring microbes in the soil that will break down ammonium and turn it into nitrate.”
“Nitrate is also another excellent source of plant food. The problem is that nitrate has a negative charge,” Kruse says. This means it will be repulsed by the negatively-charged soil. “Nitrate doesn’t stick anywhere in the soil,” Kruse says. Rain will quickly send it downwards. “It can literally just wash that nitrate down past the root zone.” This is leaching.
Not only does leaching cause farmers to lose nitrogen, it sends nitrates into the groundwater, which is not good for the environment.
N lost to denitrification
Even when they’re at the right place in the soil, nitrates are at risk of being lost through denitrification.
Kruse says, “The nitrate is a food source to a class of microbes in the soil.” Microbes need oxygen to survive. “If they run out of oxygen, they can use the oxygen that’s on nitrate as their source.” When this happens, the N03 molecule loses its oxygen and become an N2 molecule — a gas that can be lost into the air.
Denitrification can be a problem when nitrogen is applied in the fall, before a wet spring. It most commonly occurs in heavy clay soils.
You’ll make the most of your fertilizer dollar, Kruse says, “if you can protect against converting ammonium into nitrate, and keep it in the ammonium form.”
Leeann Minogue is the editor of Grainews.