Getting the right nitrogen rate for your corn

Thursday, May 1, 2014

Attempts at getting the proper nitrogen dose for your crop frequently fail. Using the Ontario Nitrogen Calculator is one way, provided it is understood. Using side dressing or nitrogen inhibitors can also reduce your nitrogen needs

by PAT LYNCH


Nitrogen is one input you do not want to run out of when you grow corn. The high yields these past few years are in part because growers are using higher nitrogen rates. You want to use a rate that provides a profit.

There is an environmental issue if nitrogen is applied and not used. Studies from Ohio suggest that we are losing about one pound of phosphorus from every acre of cropland. We are also losing 10 pounds per acre of nitrogen from every acre. The problem with nitrogen is that it changes into different forms. Once it is in a form that the plant can utilize, it is also in a form that can be lost to the air or to the tile or ground water.

Profit and environmental concerns suggest that we should try hard to apply the right rate of nitrogen.

It is not easy to arrive at the right nitrogen rate for corn. In my 40-plus years of extension work, I have witnessed three attempts to arrive at the proper rate and all failed. Our best method now is the Ontario Nitrogen Calculator. But this calculator has to be understood. It uses soil types, application time, yield and nitrogen costs.

Ontario has great soil maps showing the various soil types. You can qualify the soil on any farm, then match the nitrogen rate to a soil type. It is common to have a sandy soil in 20 per cent of a farm and heavy clay loam in 60 per cent of the same farm, with the rest of the farm in between. When you factor lower yield potential on the lighter soil and the difference in nitrogen requirements for the two soils, there is a 30-40 pounds per acre difference in nitrogen requirements. This is one place where variable rate nitrogen can work.

You can use various means to delay nitrogen getting to a form that will be lost. The most consistent of these methods is side dressing. Research indicates you can get the same yield with 10 to 30 pounds per acre less nitrogen if you side dress. The quantity by which you can reduce your total rate depends on the quantity you apply at planting. If you are shooting for 200 bushels an acre, you can reduce your total nitrogen rate by 20 to 30 pounds per acre, depending on your soil type.

I like to see 30 to 40 pounds per acre of nitrogen at planting with the rest side dress. I temper this according to the available equipment and other factors. It is common to apply 20 to 30 pounds per acre of nitrogen at planting and use another 80 to 90 pounds in a weed-and-feed program. Then the rest is side dressed.

Since the total amount of nitrogen is based on yield, it is easier to estimate yield potential when side dressing than it is at planting time. This is another benefit to side dressing.

Anhydrous used to be the product of choice for side dressing. Due to insurance and other factors, anhydrous use in Ontario has fallen. A more common method is 28 Per Cent. Various methods of drop-nozzling 28 per cent are still being tried. Some growers are broadcasting urea treated with Agrotain.

Some products are also being tried to delay the release of nitrogen until the plant needs it. Using a nitrification inhibitor is one of the ways to do this. Nitrogen inhibitors work by delaying the release of nitrogen by 15 to 25 days. This compares to the 40 to 45 days that side dressing buys you.

Another method is using polymer-coated urea (ESN). AGRIS Co-op finds that using a 75/25 blend of ESN and urea works well on lighter soils. On heavier soils, a 50/50 blend is recommended. The manufacturers of ESN tell us that 10 to 15 per cent of the nitrogen is available in 10 days, 40 per cent is available in 60 days and by 90 days it is all available. AGRIS is also treating urea with Agrotain a nitrogen stabilizer and broadcasting it on corn that is two to three feet tall. All of these techniques are being used to try and keep nitrogen in place for use by the corn plant later in the season.

The results obtained by using these methods vary. You have to balance the extra cost of these products versus the returns and the need to be environmentally responsible. Also, many growers do not like to side dress with traditional side dress equipment.

Because of all the soil interactions, it is hard to get the right nitrogen rate. By next December, we will be 90 per cent sure of what you should have used. But that should not keep us from trying. BF

Consulting agronomist Pat Lynch, CCA (ON), formerly worked with the Ontario agriculture ministry and with Cargill.