Effect of standing water levels on methane gas emission and yield performance of transplanted Aman rice (Oryza sativa L. cv. BRRI dhan51)

An experiment was conducted to investigate the effect of standing water levels on methane gas emission and yield of transplanted Aman rice (cv. BRRI dhan51) during July to December 2015 at medium low-lying area of Mohangonj upazila under Netrokona district. The experiment comprised five standing water levels on surface paddy soil viz., 5 cm, 10 cm, 15 cm, 20 cm and 25 cm. Methane (CH4) gas emission, yield components and yield of transplanted Aman rice were significantly affected by standing water levels on surface paddy soil. CH4 emission was gradually increased with rising standing water levels and remained static condition at 20-25 cm water level.  The highest CH4 emission was observed at 20 cm standing water level and the lowest CH4 emission was recorded at 5 cm water level. The highest CH4   peak recorded at 85 days after transplanting (DAT). The highest CH4 flux (36.59 mg/m2/h) was observed in treatment 20 cm water level whereas the lowest CH4flux (21.17 mg/m2/h) was observed in 5 cm water level.  Finally, the CH4 emission dropped at 108 DAT. On and average, the CH4 emission rate during rice cultivation followed 20 cm > 25 cm> 15 cm > 10 cm > 5 cm water level. Soil Eh gradually decreased with progress of time and plant growth and at 85 DAT highly reduced condition developed in all treatments. The maximum reduced condition was observed (-238.67 mV) in treatment 20 cm water level and minimum one (- 214.667 mV) was found in 5 cm water level. The highest grain (5260 kg ha-1) and straw (6725.0 kg ha-1) yields were obtained at 10 cm standing water level while the lowest grain (4191.6 kg ha-1) and straw (5050.0 kg ha-1) yields were recorded in 5 cm and 15 cm water level, respectively. It may be concluded that 10 cm standing water level is beneficial for transplant Aman rice (cv. BRRI dhan51) cultivation in low lying area in respect of grain yield and environmental issues