Influence of Biochar on Nitrogen Use Efficiency and Root Morphology of Rice-Seedling in Two Contrasting Paddy Soils

Biochar may affect the root morphology and nitrogen (N) use efficiency(NUE) of rice at seedling stage, which has not been clearly verified until now. Toclarify it, we conducted a pot experiment regarding to two soil types (HydragricAnthrosol and Haplic Acrisol), two biochar application rates (0.5 wt% and 1.5 wt%) and two rice varieties (common rice var. Xiushui134 and hybrid super rice var.Zhongkejiayou12-6) meanwhile. Seedling NUE of common rice Xiuhui134 wassignificantly increased (p < 0.05) by 78.2% in Hydragric Anthrosol and by91.4% in Haplic Acrisol following biochar addition with 1.5 wt%. However, biochar addition exerted no influence on seedling NUE of super rice Zhongkejiayou12-6 in both soils. Overall, 0.09–0.10 units higher soil pH and 105–116% higher soil NH₄⁺-N were observed in Xiushui134 growing two soils with1.5 wt% biochar. In addition, improved root morphology (including longer rootlength, larger root surface area, bigger root volume, and more root tips) contributed to the higher seedling NUE of Xiushui134 in two soils. The soil pH andNH₄⁺-N content, also the root morphology were influenced by biochar, whichthough could not thoroughly explained the NUE of Zhongkejiayou12-6. In conclusion, biochar application to paddy soil changed soil pH and NH₄⁺-N content,root growth, and the consequent seedling NUE of rice, which effects are relativewith rice cultivar, biochar addition rate, and soil type.