The reduction of nitrogen loss using biochar for soil fertility reservation

Purpose: Excessive application of nitrogen fertilizers on farmland widely occurs in China, which has been recognized as one of the main sources of non-point pollution. To reduce the nitrogen loss in agricultural soils, some specific biochar can be introduced to increase the water-holding capacity of soils and to reserve soil nutrition. The effects and mechanisms of biochar application on decreasing nutrient losses after fertilization were systematically evaluated and understood through both pot and field experiments. Materials and methods: This study was objected to investigate the effects of neutral biochar (NBC, pH 6.6–7.1) and its combination with urease inhibitor (UI) on nitrogen mitigation and reservation in farmland soil, and the interactions among the mixed soils (biochar, nitrogen fertilizer, and soil) under both pot and field experiments. Results and discussion: The application of straw biochar could reduce the amount of ammonia volatilization in soil. The maximum inhibition of ammonia volatilization loss accounted for 27.67% of fertilizer applications. In field experiments, neutral biochar could reduce the leaching of soil NH₄⁺-N and NO₃^—-N, and this effect was more evident for NO₃^—-N (68 mg/kg) compared to no fertilization in the soil layer 20–40 cm. With the addition of neutral biochar and urease inhibitors, the content of soil total nitrogen increased greatly with 1.70 g/kg. Conclusion: Neutral biochar from waste agricultural straw and commercial urease inhibitors were applied for nitrogen reservation in pot and field experiments. The application of neutral biochar played a positive role in lower volatile ammonia loss and higher nitrate content compared to urease inhibitor application only. These findings reveal the potential of neutral biochar for the improvement of agricultural soil.