Influence of Rice Establishment Methods on Water Productivity, Methane Emissions and Rice Grain Heavy Metals Content from Irrigated Rice Paddies in Bangladesh

Abstract

Reducing methane (CH4) emissions and water use in irrigated rice systems while maintaining production to feed the ever-increasing population is vital in Bangladesh. Different rice establishment methods viz. alternate wetting & drying (AWD), system rice intensification (SRI) and direct wet seeded rice (DWSR), have a promising mitigation potential to reduce CH4emission compared to continuous flooded (CF) rice fields. A field experiment was conducted at Bangladesh Agricultural University, Mymensingh, during the Boro season in 2018 to examine whether rice establishment methods could maintain grain yield with reduced water use and CH4emissions. A split-plot design was employed with water management in the main plots and fertilizer management in the subplots. The yield difference was not significant (p>0.05) in CF, AWD, and SRI systems other than DWSR. Planting methods in combination with organic fertilizer amendment had little effect on the grain Fe, Zn, and Cd concentration but significantly affected the as concentration. AWD, SRI, and DWSR significantly reduced the total water use by 17-33% and increased water productivity by 22-35% compared to CF. SRI system performed superior (p>0.05) by increasing the water productivity coupled with reducing water consumption compared to CF. The impact of water management on changing climate in rice fields was compared using seasonal CH4emission and yield-scaled global warming potential (GWP). Total seasonal CH4emissions were significantly distinct (p<0.05) from different rice establishment methods. Seasonal CH4 emissions from CF, AWD, SRI, and DWSR systems were 147.85, 128.11, 110.35, and 91.52kg CH4 ha-1, respectively. Emissions were reduced by about 13-38% in contrast with continuous flooded soil. The emissions of greenhouse gases per unit grain yield (yield-scaled GWP) followed the order; CF>AWD>DWSR>SRI, while reducing yield-scaled emissions from AWD, SRI and DWSR decreased around 15-25% over that of the CF system. In conclusion, it is recommended that both SRI and AWD can mitigate CH4 emission, powered reduce water consumption as well as grain content from irrigated rice fields without yield penalty.