Impact of silicon-rich rice husk biochar on nitrogen use efficiency in nitrogen- deficient soils with contrasting pH

Silicon (Si) enhances plant resilience under stress, where nitrogen (N) is one of the major essential nutrient elements for improving crop growth and yield. This study aimed to assess the influence of Si-rich rice husk biochar (RHB) on nitrogen use efficiency (NUE) in three N-deficient soils with varying pH by using maize ( Zea mays L.) as a test crop. A pot experiment was conducted with three N sources ( i . e ., urea, KNO ₃ and NH ₄ Cl as amide, nitrate and ammonical form, respectively) along with four RHB levels (0, 2, 4 and 8 t ha ^-1 ). Compared with other N sources, the application of KNO ₃ significantly increased plant height and biomass compared with other N sources. Increasing RHB rates further enhanced these growth parameters across all the soils. However, the combined application of RHB and N sources reduced the plant N concentration, while markedly improving N uptake, Si content and uptake. Pearson’s correlation analysis revealed a strong positive relationship between silicon accumulation efficiency (SiAE) and NUE (r = 0.95–­­0.99, p < 0.05). These findings indicate that integrating Si-rich RHB with suitable N sources enhances nitrogen utilization and crop performance in N-deficient soils. This approach presents a sustainable strategy for improving soil fertility, nutrient cycling and crop productivity under varying soil pH conditions.