Biochar applied with appropriate rates can reduce N leaching, keep N retention and not increase NH₃ volatilization in...

The impacts of biochar addition on nitrogen (N) leaching, (ammonia) NH₃ volatilization from coastal saline soils are not well understood. In this soil column study, the effects of wheat straw biochar application at rates of 0.5%, 1%, 2% and 4% by weight to a coastal saline soil on N leaching, NH₃ volatilization, soil pH and N retention were investigated. Results showed that 0.5% and 1% biochar amendments reduce the NH₄⁺-N, NO₃^--N and total N concentrations of leachate and thereby significantly decrease their cumulative lost loads by 11.6-24.0%, 13.2-29.7%, and 14.6-26.0%, respectively, in compared with the control. The biochar-induced soil N leaching mitigation efficiency was weakened when the biochar application rates increased to 2% and 4%. However, the impact of biochar addition on cumulative NH₃ volatilizations were negative and significantly 25.6-53.6% higher NH₃ volatilizations in soils with 2% and 4% biochar amended than control were detected, which was mainly attributed to the averaged 0.53-0.88units higher soil pH as results of biochar addition. On average, the total N concentrations of soil were kept same with 1.01-1.06gkg^-1 under control and biochar treatments. Therefore, biochar application to the coastal saline soils with appropriate rates (i.e., 0.5% and 1% in current study) can reduce N leaching, keep soil N retention, and not increase NH₃ volatilization, which was beneficial for sustainable use of saline soils.