Abstract
Rice is one of the world's most important cereal crops supplying 35-60% of dietary
calorie intake for about three billion people and rice farms account for 9-13% of
global greenhouse gas (GHG) emission. Nitrogen (N) and water are the two major
inputs for achieving higher grain yields of rice. The present study aimed at
evaluating the effectiveness of prilled urea (PU), urea briquette (UB) and NPK
briquette (NPK Briq) in terms of grain yield, nitrogen use efficiency (NUE) and NO
& N2O emissions from rice field under continuous standing water (CSW) and
alternate wetting and drying (AWD) conditions on rice based cropping system
(Boro-T. Aus-T.Aman) for two consecutive years (2013 and 2014). The experiment
comprised of eight treatments which were T1: control-N, T2: UB-N52, T3: UB-N78, T4:
PU-N104, Ts: UB-N104, T6: NPK briq-N51, T7: PU-N104 and Ts: NPK briq-N78 for T. Aus
and T. Aman rice, and T₁: control-No, T2: UB-N7s, T3: UB-N104, T4: PU-N156, T5: UBN156, T6: NPK briq-Ns1, T7: PU-N104 and Ts: NPK Briq-N103 for Boro rice. Sulphur and
Zinc were applied to all plots at the rate of 20 kg ha-1 from gypsum and 3 kg ha-1 from zinc
oxide, respectively. UB and NPK briquette were placed at 7-10 cm depth between 4
hills of rice at alternate rows after 10 days of rice transplanting. Ammonium
nitrogen (NH4-N) concentration of standing water was measured after deep
placement of UB and NPK Briq, and after each split application of PU. UB and NPK
briquette significantly reduced water NH4-N concentration in the rice field as
compared to PU. The grain yield of Boro rice for 104 kg N ha-¹as PU (T,) was
identical with that for 78 kg N ha-¹ as UB (T2) indicating that 25% urea saving is
possible for adoption of UDP in Boro rice under both CSW and AWD conditions. For
T. Aus and T. Aman rice, 52 kg N ha-1 (T2) either from UB or 51 kg N ha-1 (T6) from
NPK briquette showed an identical grain yield with 78 kg N ha-¹ (T7) as PU
indicating 33% urea fertilizer may be saved due to UB or NPK briquette application.
Moreover, UB and NPK briquette showed higher N recovery and NUE compared to
PU under both water management practices. AWD appears to be a good technology
without incurring loss to rice productivity during Boro season. Treatment T2 (UB52)
or T6 (NPK51) for T. Aus and T. Aman seasons and T2 (UB78) for Boro season are found
to be one of the best N management options for increasing NUE and yield of rice.
Nitrous oxide emission was recorded higher in Boro season than in T. Aus and T.
Aman seasons. Application of N as UB resulted in much lower N2O emission from
rice field under both CSW and AWD practices. The amount of NO emission was
much lower than that of N₂0 emission. Hence, combined use of UB and AWD
technologies can potentially save irrigation water, increase grain yield, nitrogen use
efficiency, and reduce N₂O emission in rice field.