Speakers - 2026

Title: Improve efficiencies and minimize losses of nitrogen through optimized management in a terrace paddy field of bangladesh

Abstract

Field experiments were conducted in dry and wet rice seasons (2021-23) at Bangladesh Rice Research Institute to assess nitrogen (N) use efficiencies and losses via leaching, gaseous NH3-N and N2O-N emission under various N managements. Selected rice cultivars were BRRI dhan89 and BRRI dhan87 for dry and wet seasons, respectively. Overall 28 (7 treatments × 4 reps.), 20m2 plots were established following RCB design. Tested seven treatments were T1:no N fertilizer+100%PKSZn (N0), T2:140 kg N ha-1 from prilled urea+100%PKSZn (N140PU), T3:T2+25% PUN (N175PU), T4:T2-25%PUN (N105PU), T5:Cow dung (2 t ha-1)+IPNS with T2 (N140 PU+CD), T6:BRRI Organic Fertilizer (2 t ha-1)+IPNS alike T4 (N105 PU+BOF) and T7:Deep Placed Urea (UDP) alike T4 (N105 UDP) for dry season. While these were T1:no N fertilizer+100%PKSZn (N0), T2:110 kg N ha-1 from PU+100%PKSZn (N110PU), T3:T2+25%PUN (N138PU), T4:T2-25%PUN (N83PU), T5:CD (2 t ha-1)+IPNS with T2 (N110 PU+CD), T6:BOF (2 t ha-1)+IPNS alike T4 (N87 PU+BOF) and T7:UDP alike T4 (N83 UDP) for wet season. Air samples were collected to analyse N2O. After each PU topdressing, NH3 emission was measured by closed chamber and boric acid trap method. Grain yields in all N fertilizer treatments were always significantly greater than that in N0 (T1). Also the yields across six N fertilizer applied treatments were statistically identical except in T4 (N105PU) during dry seasons 2021 and 2023. Agronomic N use efficiency (AEN) (kg grain kg-1 applied N) was consistently greater in T6 and T7 (27-39) than other N fertilizer treatments in dry season, which was the case for T7 (7-10) only in wet season. In both seasons, N recovery efficiency (REN) (%) was consistently greater in T7 (in dry: 55-69, in wet: 46-69) than other N fertilizer treatments. The next higher REN (%) was attained from T6 in dry season 2021 (52) and 2022 (45). Across PU-N fertilizer treatments of dry season, total NH3-N emission (kg ha-1 season-1) was significantly  greater in 25% more PU-N rate T3 (6.7-8.9) than that in T2, T4, T5 and T6 (3.2-5.8). Total NH3-N emission was significantly lowest in T1 (0-0.6) and T7 (0.1-1.1) in all seasons. Seasonal N2O emission (kg N ha-1) was significantly  greater in all N fertilizer applied treatments T2-T7 (2.0-2.5 in dry, 0.41-0.63 in wet seasons) than that in no N applied treatment T1 (0.21 and 1.1, resp.). In 2021 dry season, N leaching loss (kg N ha-1 season-1) was significantly  lower in T1, T2, T6 and T7 (1.7-3.1) than that in T3, T4 and T5 (3.2-4.2). In 2021 wet season, N leaching loss (kg N ha-1 season-1) was lower in T1, T2, T4, T5 and T7 (0.6-2.0) than that in T3 (2.8) and T6 (3.6). Therefore results on yield, AEN, REN, N losses via leaching, gaseous NH3-N and N2O-N indicate that 105 or 83 kg N ha-1 from UDP firstly, and PU+BOF secondly would be the most suitable N managements to sustain rice production and reduce environmental harm from reactive N but requires further verification via 15N isotope tracing.

Key words: Rice, Nitrogen use efficiency, gaseous losses, grain yield