Integrated effects of organic, inorganic and biological amendments on methane emission, soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims: Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods: The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^-1) + rice straw compost (2 t ha^-1) as a control, urea (170 kg ha^-1) + rice straw compost (2 t ha^-1) + silicate fertilizer, urea (170 kg ha^-1) + sesbania biomass (2 t ha^-1) + silicate fertilizer, urea (170 kg ha^-1) + azolla biomass (2 t ha^-1) + cyanobacterial mixture 15 kg ha^-1 silicate fertilizer, urea (170 kg ha^-1) + cattle manure compost (2 t ha^-1) + silicate fertilizer.

Results: The average of two growing seasons CH₄ flux 132 kg ha^-1 was recorded from the conventional urea (220 kg ha^-1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^-1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^-1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^-1) in paddy field.

Conclusion: Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.