Nitrous Oxide Production throughout the Year from Fertilized and Manured Maize Fields

Abstract Two field sites on a loam soil were established to monitor N 2 O concentration in the soil atmosphere and rate of emission from the soil surface. The sites were cropped to maize ( Zea mays L.) and managed at two high‐N levels (181 or 237 kg N ha −1 ). Both sites received 168 kg N ha −1 as feedlot cattle ( Bos taurus ) manure (preplant‐incorporated) and 13 kg N ha −1 as NH 4 NO 3 fertilizer in the row at planting. One site (Site B) received additional soil‐incorporated N (56 kg N ha −1 ) as urea. Fluctuations in N 2 O emissions from the two sites were temporally similar, and differed only in magnitude with Site A (no additional fertilizer), emitting about 3.6 kg N 2 O‐N ha −1 yr −1 and Site B about 5.2 kg N 2 O‐N ha −1 yr −1 , or about 2% of the N applied. Most of the N 2 O was emitted between mid‐June and the end of July when the soil was warm and NH + 4 ‐N was present, and at spring thaw (late March the following year) when soils were cold and near water‐saturated. High N 2 O emissions during the growing season occurred following precipitation events, and hence were associated with high soil water and probably with the initiation of soil drying. Nitrous oxide production was continuous during winter months, presumably a result of denitrification. The N 2 O concentration in the profile of the frozen soil increased to high levels (nearly 2000 µ L L −1 N 2 O at Site B) before spring thaw. At thaw, nearly 330 d after application of the N amendments, an apparent physical release period occurred and N 2 O flux was far higher (about 50 g N 2 O‐N ha −1 d −1 ) than at most times during the growing season.