On‐Farm Assessment of the Amount and Timing of Nitrogen Fertilizer on Ammonia Volatilization

Ammonia (NH 3 ) volatilization is one of the main pathways through which applied N enters the environment undesirably. A seven site‐year on‐farm field experiment was performed for 3 yr at Ottawa, ON, and 2 yr at Guelph, ON, and Saint‐Valentin, QC, Canada. Our objectives were to (i) quantify the flux and the amount of NH 3 volatilization as affected by the rate and time of N fertilizer; (ii) assess the impact of rainfall and soil temperatures on NH 3 volatilization; and (iii) determine the threshold level of N fertilizer at which large NH 3 volatilization losses occur. Using the static chamber method, NH 3 volatilization was monitored after preplant or sidedress N application. Rate of NH 3 volatilization peaked at 3 to 7 d and then dropped sharply within next 7 d before leveling off in the following weeks. The amount of NH 3 volatilization increased with increasing N levels applied preplant or sidedress at all site‐years. Peak NH 3 volatilization ranged from 40 to 8000 g N ha −1 d −1 after preplant fertilization and from about 100 to 2100 g N ha −1 d −1 after sidedress, resulting in NH 3 losses of 0.1 to 47 kg N ha −1 and 0.6 to 20 kg N ha −1 , respectively, equivalent to 0.1 to 38% and 0.3 to 13% of fertilizer‐induced emission (FIE) within 28 d after preplant or sidedress N fertilization. Our data clearly indicate that sidedress applications enable reduction in N fertilizer for economic crop yields, and may reduce losses simply due to lower total N rates.