| Summary: | Compensating nitrogen input and increasing nitrogen utilization efficiency (NUtE) are necessary for sustainable crop production. Research studies on the co-application of biochar and nitrogen to promote rapeseed growth, soil fertility, and improve nutrient utilization efficiency are found to be limited. This study aims to examine the integral effects of biochar and nitrogen over soil fertility, rapeseed growth and nitrogen utilization efficiency. The experiment was conducted in a completely randomized design to assess various morphological, physiological and biochemical traits of rapeseed and soil chemical properties under the application of four nitrogen levels (0, 75, 225, and 450 kg ha<sup>−1</sup> equivalent to 0, 133, 400 and 800 mg nitrogen pot<sup>−1</sup>) and four biochar levels (0, 5, 10, and 15 MT ha<sup>−1</sup> equivalent to 0, 10, 20 and 30 g biochar pot<sup>−1</sup> soil by weight basis). The results of this study showed that the integral application of biochar at 30 g pot<sup>−1</sup> and nitrogen at 800 mg pot<sup>−1</sup> at 45 days after sowing (DAS) and 60 days after sowing (DAS) compensated the amount of nitrogen and increased soil organic carbon (SOC 69%), total nitrogen accumulation (TNA) (93% and 62%), leaf biomass (60% and 33%), stem biomass (20% and 22%) and photosynthesis (20% and 17%) at 45 DAS and 60 DAS, respectively as compared to a single application of nitrogen. However, under the conditions of no nitrogen or 75 kg ha<sup>−1</sup> nitrogen application, the application of biochar to promote the growth of rapeseed plants is limited due to the less nitrogen supply. In contrast, the application of nitrogen at 800 mg pot<sup>−1</sup> and biochar at 10 or 20 g pot<sup>−1</sup> showed that the growth of early seedlings was adversely affected due to high nitrogen concentration in soil. The findings of the present study imply that within the appropriate nitrogen application range, the interaction of biochar and nitrogen might have an economical approach towards better utilization of nitrogen and sustainable crop production.
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