Corn School: Testing nitrogen rates on your farm


When it comes to determining the right rate of nitrogen for your farm there’s nothing better than on-farm data.

After a winter of talking with growers about escalating nutrient prices and the most economic rate of nitrogen (MERN), Ben Rosser, corn lead with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) is encouraging growers to run on-farm trials this summer to help determine the optimum nitrogen rate for their farm.

On this episode of the Corn School, Rosser shares three approaches growers can use to set up trials. “Usually the best and most accurate way to do it is to build a nitrogen response curve or ramp,” he says. In this case, growers can construct a side-by-side comparison using five nitrogen rates, starting with zero nitrogen or a starter rate. Rates can then be incrementally increased until they reach 200 lbs to 250 lbs per acre, or an appropriate target where the grower feels yield is maxed out for that field.

“That will give you a ramp and when you look at it at the end of the year you will see where yields increase and where they plateau,” says Rosser. “That optimum nitrogen rate is usually a little bit before those yields plateau.” (Story continues after the video.)

With the need for five different rates and replication, Rosser concedes that creating a nitrogen ramp does require growers to do “a fair bit” of work. A simpler approach is to use the Delta Yield method. Here, growers can use two rates — zero and a higher or “N-rich” rate. The yield difference between the zero and N-rich rate is used to assess the level of response in the field. Growers can simply use the N Rate Evaluator Tool at to estimate MERN for the field without having to test the five rates of nitrogen.

Another option is what Rosser calls the “30-pound test.” In this case, growers can do one or two strips that are 30 pounds higher or lower than their normal rate to produce five test strips.

“I’ve talked to one grower who does this every year in their corn fields,” notes Rosser. “Over a number of years he’s developed a really nice data set and he knows which fields reliably need more nitrogen, which fields he can cut rates, and how to zero in on rates across the farm and individually by field.”

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