Title : Alternate wetting and drying: a promising water saving approach to reduce methane emission without lessening yield in dry season rice
Despite enhance nitrous oxide (N2O) emission, alternate wetting and drying (AWD) irrigation reduces water input and CH4 emission over continuous flooded (CF) field with no significant yield reduction. Emission of these gases may further be impacted by broadcast prilled urea (PU) or deep place urea briquette (UB) either at their equal or differential N rates which should be evaluated for Bangladeshi paddy fields. To assess CH4 and N2O emissions, N fertilizers use efficiencies and grain yield, we set up an experiment at the paddy field managed by Soil Science Division of Bangladesh Rice Research Institute (BRRI) from January to April, 2020. The cultivated rice variety (BRRI dhan81) was grown under CF and AWD irrigations, with (broadcasted PU N: PUN120/78 or deep placed UB N: UBN78) or without N fertilizer application (N0). Gas samples were collected regularly by closed chamber and analyzed by GC, to compare CH4 and N2O emissions. To record grain yield 125 hills plot-1 (~ 5m2) was harvested. Grain yield in all N fertilized plots were significantly (p<0.01) greater than that in N unfertilized plots (N0). However, water management and its interaction with N fertilizer treatments had no significant effects on grain yield (p = 0.756 and p = 0.112, resp.). The recovery (REN: 17-54%), physiological (PEN: 30-45 kg grain kg-1 N uptake) and agronomic (AEN: 13-25 kg grain kg-1 N applied) efficiencies were in line with previous studies. In each irrigation management, the recovery (REN), physiological (PEN) and agronomic (AEN) efficiencies at UBN78 were closer to that in PUN120. Irrespective of N fertilizer treatment, overall CH4 emission fluxes were greater in all CF plots than that in AWD particularly from 36 to 70 DAT. Cumulative seasonal CH4 emission were significantly lower in AWD than CF (p<0.01) but did not statistically differ between N fertilized and unfertilized treatments (p = 0.118). Also the interaction effects of N fertilizer and water management on seasonal CH4 emissions were insignificant (p = 0.439). Seasonal CH4 emission was decreased by 70 (in AWD-UBN78), 86 (in AWD-PUN120), 102 (in AWD-PUN78) and 177 (in AWD-N0) kg CH4 ha-1 resp., over corresponding treatments under CF which equals 20-41% reduction in CH4 emission under AWD. The yield scale seasonal CH4 emission (in kg CH4 ha-1 t-1 grain yield) ranged from 48-72 in AWD and 65-130 in CF with its lower values in PUN120-AWD (48) and UBN78-AWD (56), and higher values in PUN120-CF (65) and UBN78-CF (73). So, UBN78-AWD seemed almost equally capable to reduce seasonal CH4 emission and provided comparable N fertilizer use efficiencies with that in PUN120-AWD, but requires further verification in more paddy fields.