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Integrating fertilizer nitrogen (N) with organic manures can foster a sustainable agricultural system in subtropical soils low in organic matter. A two year field experiment was conducted on a sandy loam soil at Allahabad, India to evaluate the effect of incorporating spent white button mushroom compost (WB-SMC) with a narrow C:N ratio (15.18) and spent oyster mushroom compost (OY-SMC) of a wider C:N ratio (37.58) with and without fertilizer N on rice crop production, N use efficiency and soil carbon (C) sequestration. A higher paddy, straw yield and total dry matter production of 5.00, 6.24 and 11.24 t ha-1 in WB-SMC at 5 t ha-1 with fertilizer N at 90 kg ha-1 and 5.26, 6.80 and 12.05 t ha-1 in WB-SMC at 5 t ha-1 with fertilizer N at 120 kg ha-1 confirmed the superiority of the WB-SMC over OY-SMC, which produced 3.57, 4.62 and 8.18 t ha-1 with fertilizer N at 90 kg ha-1 and 4.17, 5.32 and 9.48 t ha-1 with fertilizer N at 120 kg ha-1 respectively. When WB-SMC was applied at 5 t ha-1 it enhanced the recovery efficiency of 19.62 and 15.56 % compared to fertilizer N at 90 and 120 kg ha-1 respectively. Physiological efficiency due to luxury uptake of N with the use of WB-SMC and fertilizer N at 120 kg ha-1 gave evidence that N addition through the combined use of WB-SMC and fertilizer N was excessive. Agronomic efficiency of added N by the rice crop was improved by the incorporating WB-SMC at 5 t ha-1 and fertilizer N at 90 kg ha-1. Despite a wider C:N ratio, OY-SMC gave higher soil C sequestration in flooded rice than WB-SMC in the presence or absence of fertilizer N. [ABSTRACT FROM AUTHOR]