The Role of Biochar in Soil Nitrogen Cycle

Biochar is a black solid containing stable carbon with many positive effects on the physical, chemical, and biological properties of soil. One important positive effect of biochar on soil is its contribution to nutrient (e.g., nitrogen) mobility and dynamics in soil. Negatively charged on the surface, biochar is capable of adsorbing and storing ammonium ions (NH4+) and small nitrogen-containing organic molecules. It also releases nitrogen into the soil to change the carbon to nitrogen ratio (C/N), whereby the mineralization-immobilization balance of nitrogen is affected. Moreover, biochar indirectly affects soil nitrogen cycle and dynamics by changing such soil properties as pH, cation exchange capacity, electrical conductivity, organic carbon, biological activity, nutrient availability, porosity, ventilation, and water relations, among others. It is through these changes that water, air, and nutrients are provided to make soil a suitable habitat favorable to soil microorganisms that help improve biological fixation of nitrogen. Biochar also reduces N2O emission, as a greenhouse gas, from the soil by reducing soil nitrogen sublimation. In general, biochar has a synergistic interaction with nitrogen and can enhance nitrogen use efficiency to reduce nitrogen fertilizer consumption. However, only scant knowledge is presently available on soil nitrogen changes induced by biochar, especially in calcareous soils. Further research is needed to investigate the effects of biochars produced from different types of biomass under different temperatures on the mobility and availability of nutrients, especially nitrogen, in calcareous soils.