Soil-Dependent Effects of Rice Husk Biochar on N2O Emissions from Compost-Amended Agricultural Soils

This study tested whether the N2O response to increasing rates of the same rice husk biochar differed between two chicken compost-amended agricultural soils. A clay loam paddy soil and a loam vegetable soil were amended with 2% (w/w) chicken compost and 0, 0.5, 1.0, or 1.5% (w/w) rice husk biochar, then incubated without plants in a small-scale laboratory experiment at 30 °C and 60% water-holding capacity for 28 days. Soil pH, electrical conductivity, NH4+-N, NO3−-N, and N2O emissions were monitored. At 1.0% biochar, cumulative N2O emissions decreased from 4.4 to 2.5 mg N kg−1 in the clay loam soil and from 6.8 to 3.8 mg N kg−1 in the loam soil, reductions of approximately 43% and 44%, respectively. Increasing the rate to 1.5% provided no additional mitigation in the loam soil and substantially weakened mitigation in the clay loam soil. Soil, biochar rate, and their interaction significantly affected cumulative emissions (p < 0.001). Thus, the biochar rate-response was not uniform between the two soils tested.