On-farm assessment of the amount and timing of nitrogen fertilizer on ammonia volatilization
Ammonia (NH3) 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 NH3 volatilization as affected by the rate and time of N fertilizer; (ii) assess the impact of rainfall and soil temperatures on NH3 volatilization; and (iii) determine the threshold level of N fertilizer at which large NH3 volatilization losses occur. Using the static chamber method, NH3 volatilization was monitored after preplant or sidedress N application. Rate of NH3 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 NH3 volatilization increased with increasing N levels applied preplant or sidedress at all site-years. Peak NH3 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 NH3 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.