Improved N application methods and N sources for corn in Southwestern Ontario

Increased farm sizes and greater urgency for timeliness have resulted in greater time constraints for producers to apply N fertilizers to crops. Hence, some producers have now started applying their N by either streaming urea-ammonium nitrate (UAN) or broadcasting urea onto their soils. They are considering adding inhibitors with urea or UAN to reduce losses of applied N. The increased use of urea and UAN fertilizers compared to other N sources may also enhance N losses through ammonia volatilization and/or denitrification (nitrous oxide) and dinitrogen (N₂) emissions). The objectives of this study were to: 1) determine the amount of ammonia lost following side-dress N application; 2) determine the effectiveness of injecting or streaming N application in reducing ammonia volatilization losses compared to broadcast application; 3) evaluate the ability of urease and nitrification inhibitors to reduce ammonia volatilization and nitrous oxide emissions; and 4) determine the crop response to the various N sources and application methods. This study was started in April 2014 and this is the first year of the co-operative study. The treatments investigated included three application methods (broadcasting, streaming and banding N fertilizers) and three different N sources (the regular N source [urea for broadcast and UAN for streaming and banding], the regular N source with a urease inhibitor and the regular N source with a urease inhibitor and a nitrification inhibitor). A control N treatment (zero rate) was included for comparison.

Ammonia volatilization measurements were obtained daily using wind tunnels over the first 28 days after application. Weekly measurements of nitrous oxide emissions were obtained throughout the growing season. Every three weeks, soil samples and five plant samples were taken to examine the amount of inorganic N remaining in the soil and the plant biomass and plant N uptake.

Dramatic differences were obtained in ammonia volatilization losses. In general, the broadcast urea resulted in the greatest ammonia volatilization losses (~28% of N applied). When a urease inhibitor was included with the urea or the N was injected into the soil, ammonia losses were reduced more than fourfold. The nitrous oxide emissions from this growing season are being analyzed on a gas chromatograph.

Initial data and observations collected up to January 2015 indicate that N source and placement impacted both ammonia losses and crop yield responses.