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Sidedress to Minimize Potential N Loss



Denitrification, leaching minimized by sidedressing prior to corn’s V8 growth stage.00436_Fast_Sidedressing_1200x628_Graphic.jpg

Mother Nature is not doing corn farmers many favors this spring. She’s thrown up weather stumbling blocks from day one ranging from heavy rainfall and flooding to late-season snowfall after a winter that seemed to never end for some farmers.

Most of the conjecture about the weather holdups this year has centered around major field operations like planting. But the corn crop’s ultimate productivity this year will hinge on more than simply hitting the optimal planting window. Other field operations throughout the crop year could happen either outside the ideal timeframe or in poor conditions, making it difficult to achieve desired results. 

Applying nitrogen (N) fertilizer is one of those operations whose efficacy depends on both timing and field conditions. Given the tight timeframe for getting everything done in the field this spring, some nitrogen applications might happen in less-than-perfect conditions. One way to avoid the performance drag of mistimed applications or those done in poor field conditions is by sidedressing nitrogen — injecting it into the soil instead of applying on the surface where it’s susceptible to loss before corn plants have a chance to utilize it.

Potential N losses in wet soils

First, it’s important to know what you’re up against when potentially applying nitrogen when soils are too wet. Two of the main causes for nitrogen loss — denitrification and leaching — are much more likely in wet field conditions and increase the likelihood that only part of what you apply will actually be taken up by corn plants. For example, research by North Dakota State University Soil Science Professor Amitava Chatterjee shows when urea is applied when soils have 80% of its water-holding capacity (WHC) remaining, almost 16 times more nitrogen will be available to the crop planted there than when nitrogen is applied when the soil has only 30% of its WHC available.

"A considerable amount of applied urea N is subjected to denitrification loss of more than 60% WHC," Chatterjee said. "Efficient N fertilizer management includes avoiding N application at the times of excessive rainfall, irrigation or spring thaw events."

Preventing nitrogen loss

Denitrification and leaching — the loss of nutrients on soil’s surface caused by running water and erosion — can be minimized by sidedressing a nitrogen application. Following a pre-plant application, a sidedressed application puts fertilizer immediately adjacent to young corn plants, usually around the V5 or V6 growth stage. This helps narrow the window in which fertilizer can be lost in wet soils where denitrification and leaching are both more common than in drier soils. Research shows in-season nitrogen applications begin to lose efficacy at around the V8 growth stage for corn.

“Independent yield studies have shown that there is a benefit to split application of nitrogen as a way to increase yields and minimize potential nitrogen loss,” said Mountain Lake, Minnesota, farmer Cody Fast. “We also feel there is a benefit to giving our corn a shot of nitrogen right before ear size is determined at V5 or V6 rather than skipping this critical growth stage and waiting until later in the season which multiple independent yield studies also back up.”

The right tools for the jobArticle_Banner_pic.jpg

Especially when soils are damp (provided conditions allow a pass through the field), injecting nitrogen using a machine like a FAST liquid fertilizer applicator helps get fertilizer where it is intended. Beyond the benefit of applying fertilizer, like urea ammonium nitrate (UAN), below the soil’s surface and making it more immediately available to crops, sidedress applications helps better sustain more consistent year-over-year soil fertility by minimizing nutrient loss from causes commonly associated with surface applications.

“We variable-rate sidedress 20 to 30 gallons of 28% UAN per acre along with ammonium thiosulfate (ATS) with our FAST 2,400-gallon applicator on CAMSO 15-inch tracks,” Fast said. “This is in addition to our pre-plant pass with our FAST sprayer where we use 28% and ATS as a carrier along with pre-emerge herbicide.”

Long-term nutrient consistency

Beyond the benefit of more precise nitrogen applications each spring, sidedressing helps maintain more consistent soil fertility. In the long run, more consistency in soil nutrition helps streamline year-over-year crop management, even in years of major variability in growing conditions like 2019.

“We know that rainfall varies tremendously in early summer and we feel that injecting our nitrogen into the ground rather than dribbling it on top is our safest way to apply it and minimize potential loss. We rely on timely rainfall enough in our farming operation,” Fast said. “We feel much more secure year-over-year knowing that our nitrogen is already in the ground and it moves with the water in the soil profile to the corn roots.”