It is generally assumed that fertilizer addition is the prime driver of nitrogen (N) gas loss from modern cropping systems. This assumption has its basis in observations of nitrous oxide (N₂O, an important greenhouse gas) emissions, and is contrary to theory from unmanaged ecosystems, where N losses are controlled by plant physiological influence on the soil environment. However, dinitrogen (N₂) emissions are likely a major N loss pathway in both managed and unmanaged ecosystems, but these emissions are very difficult to measure. We directly measured N₂ and N₂O emissions from two temperate agricultural systems over the course of the growing season to test when total N gas losses are highest. We hypothesized that N₂ emissions mirror those of N₂O, with the largest flux immediately after fertilization, early in the growing season. Instead, we found that N₂ emissions were highest at the end of the growing season, and were most strongly correlated with soil moisture, which increased after plant senescence. Dinitrogen emissions were an order of magnitude larger than N₂O. Thus, while N₂O emissions were highest following fertilization, overall N gas loss was greatest at the end of the growing season. These data suggest that total N gas losses are high and have different temporal patterns from N₂O fluxes. Understanding the magnitude and controls over these losses are important for understanding and managing the N cycle of temperate agricultural systems.

人们普遍认为，肥料添加是现代耕作系统氮 (N) 气体损失的主要驱动因素。这一假设以一氧化二氮（N ₂ O，一种重要的温室气体）排放的观测为基础，与不受管理的生态系统的理论相反，在该生态系统中，氮的损失是通过植物对土壤环境的生理影响来控制的。然而，二氮 (N ₂ ) 排放可能是管理和非管理生态系统中主要的氮损失途径，但这些排放很难测量。我们直接测量了两个温带农业系统在生长季节的 N ₂ 和 N ₂ O 排放量，以测试总氮气体损失何时最高。我们假设 N ₂ 排放量与 N ₂ O 排放量相似，在受精后即生长季节早期具有最大通量。相反，我们发现氮 ₂ 排放量在生长季节结束时最高，并且与土壤湿度的相关性最强，土壤湿度在植物衰老后增加。二氮排放量比 N ₂ O 大一个数量级。因此，虽然 N ₂ O 排放量在施肥后最高，但总体氮气损失在生长季节结束时最大。这些数据表明，总 N 气体损失很高，并且与 N ₂ O 通量具有不同的时间模式。了解这些损失的严重程度和控制措施对于理解和管理温带农业系统的氮循环非常重要。