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Urea deep placement (UDP) has demonstrated its benefits of saving N fertilizer and increasing nitrogen use efficiency (NUE) and grain yields. However, studies on its environmental impacts, particularly on nitrous oxide (N2O) and nitric oxide (NO), are limited. We conducted multi-location field experiments in Bangladesh to determine the effects of UDP versus broadcast prilled urea (PU) on N2O and NO emissions, NUE, and rice yields. N2O and NO emissions were measured from three N fertilizer treatments—no N, UDP, and PU—using automated gas sampling and analysis systems continuously for two rice-growing seasons—Aus (May–August) and Aman (August–December). Fertilizer-induced peaks in N2O emissions were observed after broadcast application of PU but were rarely observed after UDP. Total seasonal N2O and NO emissions, yield-scaled emissions, and fertilizer-induced emissions were affected by fertilizer treatments and sites. Though nitrogen fertilizer increased emissions significantly over the control, emissions resulting from UDP and PU were similar. Effects of N placement on grain yields and NUE were site- and season-specific. Of the N placement methods, UDP increased grain yields by 13% (p < 0.05) during the Aman season and gave similar yields in spite of lower N application during the Aus season. UDP increased N recovery from 25 and 16% of broadcast PU to 61 and 73% during the Aus and the Aman seasons, respectively in one site, but was similar in another site. On the other hand, alternate wetting and drying irrigation reduced grain yield and N recovery at the BRRI site during the Aman season. [ABSTRACT FROM AUTHOR]

Urea deep placement (UDP) increases nitrogen use efficiency (NUE) in lowland rice fields by reducing ammonia volatilization, surface runoff and increasing nitrogen uptake. However, its effects on N losses as nitrous oxide (N 2 O) and nitric oxide (NO) are not yet clear. We conducted field experiments at two locations of Bangladesh — Bangladesh Agricultural University (BAU) and Bangladesh Rice Research Institute (BRRI) — to determine the effects of UDP vs broadcast urea on N 2 O and NO emissions from rice fields. N 2 O and NO emissions were measured from three N fertilizer treatments (control [0 kg N/ha], UDP, broadcast urea) using automated gas sampling and analysis system continuously for three rice growing seasons — Aus (May–Aug), Aman (Aug–Dec) and Boro (Jan–May). Urea was applied as 2–3 split application, while for UDP treatment, urea briquettes were deep placed (7–10 cm depth) between 4 hills of rice at alternate rows to meet recommended N rates in a single application. Treatments were arranged in a randomized complete block design with three replications and N 2 O and NO measurements were done at every three-hour interval. N 2 O emissions were sporadic and event specific. Peaks in N 2 O emissions were observed after broadcast application of urea, during dry period and after re-flooding of the dry soil. For the rest of the time during the rice-growing season, emissions were very low to negligible. However, across the rice-growing seasons, UDP significantly (P < 0.05) reduced N 2 O emissions compared with broadcast urea. Moreover, N 2 O emissions showed significant spatial and seasonal variations. They were higher during Boro season compared with Aus and Aman seasons and at BAU site than that of BRRI. Conversely, emissions between Aus and Aman seasons and between control and UDP treatments were similar. In contrast to N 2 O emissions, NO emissions were negligible and not affected by fertilizer treatment. However, significant spatial and seasonal variations were observed, with higher NO emissions at BRRI site compared with BAU and during Boro than that of Aus season. [ABSTRACT FROM AUTHOR]