Integrated Nutrient Management and Urea Deep Placement Improve Rice Yield, Nitrogen Use Efficiency and Farm Profits Without Affecting Methane Emissions in Saline Soils of Bangladesh

Abstract
Soil salinity is one of the major yield-limiting factors in the coastal ecosystems of Bangladesh.An efficient fertilizer management practice and selection of appropriate crop cultivar could play a crucial role to improve yield and promote low-carbon agriculture across saline soils. A two-year multi-location field experiment was conducted during the Boro (dry) season to investigate the effects of fertilizer management and rice cultivar selection on rice yield, economic viability, and environmental sustainability in coastal saline soils of Bangladesh. The study included seven fertilizer treatments with varying nitrogen rates and sources, as well as two rice cultivars (BRRI dhan67 and BRRI dhan88). The results showed that integrated nutrient management (INM-N84) significantly increased rice yield and nitrogen use efficiency (NUE) compared to other treatments for both BRRI dhan67 and BRRI dhan88. Similarly, INM-N84 gave a higher return on fertilizer investment and marginal benefit-cost ratio than other treatments in both locations and under both cultivars. BRRI dhan67 outperformed BRRI dhan88, significantly increasing rice yield by 21% and 52% at the BRRI farm and Kaliganj in Satkhira, respectively. Cost-dominant analysis excluded BRRI dhan88 and all fertilizer treatments, except UDP and INM-N84, from consideration in both locations. Consequently, INM-N84 and UDP proved to be economically viable in both locations, with INM showing a higher marginal rate of return than UDP in BRRI dhan67. In terms of environmental sustainability, UDP significantly (p<0.05) reduced global warming potential (GWP) and yield-scaled emissions (YSE) of CH4 by 31% and 38% without causing yield loss compared to INM-N84. Similarly, BRRI dhan67 significantly (p<0.05) reduced GWP and YSE of CH4 by 5 and 22% compared to BRRI dhan88. These findings suggest that selecting optimal rice cultivars and implementing appropriate fertilizer management practices can enhance economic profitability, ensure food security, and mitigate the adverse effects of climate change in coastal saline soils.
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