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Calculator To Determine N Rate

“I think there is tremendous potential for this calculator. I can assure you that something like this is going to become a valuable tool in the farming community.”

– DON FLATEN

When nitrogen prices went through the roof a few years ago, farmers flooded John Heard with queries about determining the optimum economic application rate for nitrogen.

It’s not an easy question to answer, said Heard, Manitoba Agriculture, Food and Rural Initiatives’ (MAFRI) soil fertility specialist. There are a lot of variables to consider, such as the price of nitrogen, how much residual nitrogen remains in the top two feet of soil, the crop being grown, its yield potential and expected price.

After working a few scenarios out, Heard said one thing is absolutely clear: a doubling of nitrogen prices does not mean farmers should cut their nitrogen rate in half. In fact, if crop prices go up enough the optimum economic rate of nitrogen won’t change.

Now there’s an interactive spreadsheet program available on MAFRI’s website http://www.gov.mb.ca/agriculture/financial/farm/nitrogencalc.htmlthat takes much of the guesswork out. However, since certain assumptions are made about potential yields and crop prices, Heard said farmers should use the information as a guideline, not a recommendation.

The critical feature is that the calculator is based upon updated field research, which modernizes the relationship between nitrogen rates and yield response.

It allows users to plug in nitrogen prices, levels of residual nitrogen in the soil, the amount of nitrogen the farmer wants to add and crop prices for wheat, barley and canola.

Oats and winter wheat will eventually be added to the calculator too.

When nitrogen is relatively cheap, say 30 cents a pound, it’s a no-brainer – farmers can apply the optimum agronomic rate and be well within the optimum economic return.

For example, if nitrogen is 30 cents a pound and a farmer is growing wheat in a “moist” part of the province, with 30 pounds an acre of residual nitrogen and expects a return of $5 a bushel, the calculator says the optimum economic rate of nitrogen to apply is

110 pounds an acre, resulting in a net return of $287 an acre.

If everything stays the same, except the expected price of wheat is $7 a bushel, the optimum economic nitrogen rate jumps to 120 pounds an acre, resulting in a net return of $416 an acre.

If the farmer is nervous about the potential yield or prices, dropping the rate back to 90 pounds still produces a net return of $407 an acre. In this scenario, applying

30 pounds an acre less nitrogen, only reduces the net return by $9 an acre. When nitrogen is cheap and crop prices are high, there’s little economic reason to be conservative, unless there’s some reason to believe yields will be down.

But things change when crop prices are low and nitrogen is expensive. If wheat is $5 a bushel, but the price of nitrogen is 89 cents a pound the optimum economic nitrogen rate drops to 70 pounds an acre, resulting in a net return of $232 an acre.

If nitrogen is 89 cents a pound but wheat is $7 a bushel, the optimum economic rate jumps to 90 pounds an acre, producing a net return of $354 an acre.

The results are much different if you’re growing wheat in an “arid” area where it is lack of moisture, more than lack of nitrogen that limits yields. If nitrogen is 89 cents a pound and wheat is $7 a bushel the calculator puts the optimum economic nitrogen rate at just 30 pounds an acre producing a net return of $207 an acre. Cutting the rate to 20 pounds drops the return by just 10 cents an acre.

The calculator shows under this scenario that if the price of wheat turned out to be $5.50 a bushel, the net return after applying 30 pounds of nitrogen an acre is $157. Had the farmer applied 50 pounds of nitrogen instead of 30, he or she would have lost $9.20 less return an acre. And had the farmer applied 60 pounds, the reduction in return would be $23.50.

Obviously these computations cannot be done on the back of an envelope, but they can be using a computer-based calculator.

The data used in the nitrogen calculator comes from 20 years of nitrogen yield response trials conducted by Westco (Western Co-operative Fertilizers Ltd.), now a division of Viterra. In 2004, the Agri-Food Research and Development Initiative (ARDI) gave Westco a $35,000 grant to pull the data together on behalf of the Manitoba Soil Fertility Advisory Committee chaired by Heard. Rigas Karamanos, Viterra agronomy manager, provided most of the interpretation in conjunction with guidance and review by other Manitoba scientists and agronomists who comprise the committee.

“I think there is tremendous potential for this calculator,” said committee member and University of Manitoba soil scientist Don Flaten. “I can assure you that something like this is going to become a valuable tool in the farming community.”

MAFRI’s previous nitrogen rate recommendations were based on older crop varieties and some of the trials included summerfallow fields and didn’t include minimum-or no-till fields. [email protected]

About the author

Reporter

Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.

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