Rethinking nitrogen losses

NEW RESEARCH ANALYSES WHICH PRACTICES RESULT IN THE MOST LOSSES

even with nitrogen (n) prices that have fallen considerably over the last two years there are good reasons to continue to fine tune your N strategies. Nitrogen costs still represent a significant portion of your total crop budget and prices will most likely see a return to higher levels. The loss of N also contributes to environmental concerns that might be as global as atmospheric warming or as local as your own water well.

research in the field
This past summer, researchers at OMAFRA?and the University of Guelph have continued to explore techniques for evaluating N losses from various forms of N and application strategies. Specifically, the work focused on losses from ammonia volatilization. The approach is relatively simple and has been developed by Dr. John Lauzon and his graduate students at the University of Guelph. The nitrogen is applied and then immediately covered with a chamber (full of holes) to somewhat trap the ammonia; in our case we used blue recycling bins (see photo 1). Inside the chamber is a small glass vial which is packed with a material that reacts with the ammonia and produces a colour change indicating the amount of ammonia released into the chamber. The vial can be read periodically and gives a cumulative total.

PHOTO 1. ARRANGEMENT FOR MEASURING AMMONIA VOLATIZATION (N LOSS) FROM PLOTS.

TABLE 1. SUMMARY OF AMMONIA LOSS DEMONSTRATIONS DONE AT RIDGETOWN, ELORA AND WINCHESTER IN 2010.

In 2010 we applied similar treatment to plots at three locations in conjunction with the Ridgetown Diagnostic Days, Elora FarmSmart Expo and the Eastern Crop Diagnostic Day in Winchester. The big challenge with the approach is trying to come up with a reliable calibration that takes the parts per million reading in the chamber to an estimate of real world N losses in pounds per acre. This work is ongoing but for the interest of this article we will present the losses as a relative index in order to compare treatments. Remember also that since the chambers allow very little rainfall to reach the soil these losses are essentially comparing the potential losses if two weeks elapsed after application without rainfall and with relatively warm temperatures.

nitrogen loss results
For the pre-plant treatments surface applications of urea left unincorporated had the highest losses, as expected. We have expressed this as an index of 100 and our best estimates suggested that more than 50 percent of the total N applied was lost due to ammonia volatilization. Environmentally Smart Nitrogen (ESN) was also surface applied and although the total N losses were significantly reduced, this data did not indicate the ESN losses would be zero if left on the soil surface for two weeks without rain.

Of course the vast majority of urea in the province gets incorporated with tillage and the results indicate that this is quite effective at minimizing losses; even a single shallow pass (like you might experience with a vertical tillage tool) cut losses by 60 percent and a more aggressive single pass reduced losses by 84 percent.

The research also compared spraying UAN on the soil surface at planting. Since urea is the source of the volatilization and UAN is comprised of roughly 50 percent urea we would expect losses to be cut by one half.  In reality they were reduced by more than 50 percent when surface applied, but were still higher than urea moderately incorporated.

The lowest losses (near zero) at all three sites were always the plots where UAN was surface applied and then lightly incorporated with tillage.

In the next range of plots at each location N was applied as UAN at side-dress time. We compared side-dressing where the injection was deep (three to four inches) and the UAN completely covered to treatments where it was dribbled on the soil surface or where it was poorly injected (approximately one inch deep) but where the UAN could often be seen at the bottom of the shallow trench. Consistently the losses from the good job of injection were very low and somewhat surprisingly the surface applied or shallow injection resulted in significantly higher N losses.

PHOTO 2. STREAMER NOZZLE APPLICATONS OF UAN BEING EVALUATED BY THE PEEL COUNTY SOIL AND CROP IMPROVEMENT ASSOCIATION.

so what?
This work will be repeated in future experiments to confirm some of the numbers and to arrive at more reliable estimates of actual N loss. However, the observed results of this research have been consistent enough for us to arrive at some tentative conclusions.

It almost always took four to five days before ammonia losses were detected even from the surface applied urea under relatively warm conditions. However, the cool conditions that prevail when  applying urea to winter wheat fields in March or April will often delay volatilization until a rainfall moves the nitrogen into the soil matrix.

This research also revealed that even fairly modest amounts of tillage can significantly reduce the losses from surface broadcast urea. Although this may be less likely if surface plant residue levels are high. But, when it comes to surface applications UAN seemed to be much less prone to loss than urea and a shallow incorporation of the UAN essentially dropped losses to near zero.

For UAN applications at side-dress timing, our numbers clearly suggest that it is worth the time to get the coulters and injectors working properly to cover the UAN. Surface applications of UAN at side-dress time or poor covering of the UAN by the side-dress applicator did result in much higher N losses than correct injection.

For those producers using spray rigs to apply UAN with streamer nozzles into six inch high corn in early June this work does pose reasons to at least consider timing, temperature and rainfall forecasts as tools to minimize potential N loss. Future work will provide more detail into pros and cons of this approach over N injection. 

This research was funded in part through Growing Forward, a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of several Growing Forward programs in Ontario. •

About Greg Stewart 24 Articles
Corn Specialist, Ontario Ministry of Agriculture, Food and Rural Affairs