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The appeal of late N applications in corn

June 20, 2014, Ontario – Recently there has been a fair bit of attention paid to late applications of nitrogen (N) in corn. Three things have contributed to this excitement: 

1. Equipment that can deliver N (principally 28 per cent - UAN) into much taller corn than traditional tractor-drawn sidedress equipment. This includes high clearance sprayers equipped with injection coulter toolbars or drop tube systems. 

2. American high corn yield contest winners have been speaking in Ontario about how late (around tassel emergence time) N applications boost corn yields to new heights. 

3. Research in the U.S. corn belt has shown that new hybrids tend to take up more N post-silking than older hybrids. When this research was recently summarized, the amount of N taken up post-silking averaged 37 per cent of the total crop uptake of N (Pioneer Crop Insight, March 2014). 

Here are a few reminders to consider as we search for improved corn yield and improved nitrogen-use efficiency through later applications of nitrogen. 

1. Ontario research supports the idea that split applications of N improve profit potential, especially if better N rate decisions based on rainfall, yield potential, soil nitrate status and crop colour can be made. The movement to high clearance equipment widens the window to make these “split” applications, and this may be a critical step forward in improving N management. However, if “improved” N rate decisions are not part of the system and we simply apply the same amount of N but do it in two applications rather than one, the profit improvement will not be as great. 

2. While we consider 30 pounds of N per acre adequate to carry a corn crop to the typical sidedress window, it will likely be insufficient to carry a crop to waist high or beyond. Sixty to 100 lbs/acre is probably a safer early season N rate. 

3. Applying 240 lbs/acres of N early in the season and then coming back with another 60 lbs/acre at tassel time to win a yield contest is a much different context than applying 100 lbs/acre early and then coming back with 60 lbs/acre later to try to get improved yields. Dry soils, lack of soil incorporation, or no rainfall after the application of N may result in the N supply being restricted to the corn plant and therefore a considerable risk of lower yields if only 100 lbs of N is actually available during peak demand periods. 

4. The risks of not getting the N into the soil matrix are real and they increase as you delay N application later into the season. As we move to understand late applications of N and how to manage the options, it might be best to consider waist-high applications as a less risky option than waiting to chest high or tasselling corn. 

We look forward to researchers, corn producers and industry personnel working together to refine nitrogen management systems that fit with modern high yielding hybrids and generate improved profitability and greater efficiencies in the way we use N fertilizers. 2014 will generate a significant amount of Ontario experience on later, high clearance applications of N in corn. Keep an eye out for these developments. 

June 20, 2014  By Greg Stewart OMAF


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