Abstract
Rice is the dominant cereal in Bangladesh; 75% of the country's total cropped land
is under rice production, annually producing approximately 34 million tons of
paddy rice. Nitrogen (N) and water are the two major inputs for achieving a higher
grain yield of rice. Two pattern-based experiments, i.e., i) Mustard - Boro rice - T.
Aman rice and ii) Boro rice - T. Aus rice - T. Aman rice, were conducted at Soil
Science Field Laboratory of Bangladesh Agricultural University, Mymensingh, for
three consecutive years to evaluate the effects of different forms of N fertilizer and
water management practices on yield performance, N recovery and CH4 and N2O
emissions from rice fields. The experiments were laid out in a randomized complete
block design with three replications. Different forms of N fertilizer were used, viz.
prilled urea (PU) and urea briquettes (UB). During the Boro season, continuous
standing water (CSW) and alternate wetting & drying (AWD) water management
were tested. Different N fertilizer applications for rice crops were broadcasting of
PU, deep placement of PU and deep placement of UB. For the mustard crop, N
fertilizer was applied by broadcasting. Manures like poultry manure (PMМ),
vermicompost (VC) and cowdung (CD) were applied in both Boro rice and T. Aus
rice. Deep placement of N fertilizers in the form of UB or PU minimized N losses
and enhanced N use efficiency. It also improved the growth and yield of rice. Urea
deep placement (UDP) showed better performance and significantly reduced
floodwater NH4-N and NH3 volatilization compared to broadcast PU. Urea deep
placement increased grain yields and N use efficiency over broadcast PU and
reduced GHG emissions compared to broadcast urea. N2O emission factor for UDP
in Boro rice, T. Aus rice & T. Aman rice was 0.12, 0.14, & 0.17 and that for PU was
0.40, 0.46, and 0.55, respectively. The AWD reduced 10% CH4 emission compared
to CSW. Shorter-duration variety cut CH4 emissions by 40.5 %. Urea briquette deep
placement reduced the use of PU fertilizer by 25%. The UDP significantly reduced
the amount of N in floodwater compared to PU. Ammonia volatilization loss was
negligible with UDP, while volatilization from PU treatments increased with
increasing N rates. Crop response to fertilizer was similar between CSW and AWD
water regimes. However, UDP, either as PU or as UB, increased rice yield by 4.0 -
31.2% compared to PU. Hence, the combined use of UB and AWD technology can
save irrigation water, increase grain yield and N use efficiency, and reduce CH4
and N2O emissions in rice production.