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

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.