Ammonium and nitrate sorption by biochar

Abstract: Biochar has recently drawn attention due to its ability to increase soil fertility, sequester carbon and its expected effect on reducing the leaching of elements from the soil, especially nitrogen. The possibility of using biochar as a soil amendment to reduce the amount of nitrogen leaching, and then reducing the quantities of nitrogen fertilizers used in agriculture to avoid the bad environmental effects has become a matter of great interest. In this study, the possibility of using biochar to reduce nitrogen leaching from soil was investigated by studying the adsorption capacity and subsequent release of ammonium (NH4 + ) and nitrate (NO3 - ) from three different biochars, vermiculite, perlite and two synthetic ion exchange resins (cation and anion exchangers). The release of NH4 + and NO3 - over time from biochars and other materials were studied with a dialysis bag method. Through the comparison of desorption between the materials with known charge and porosity properties the potential sorption mechanisms by biochar is discussed. All three kinds of biochar had negligible capacity to retain NO3 - . The biochar behaved similarly to the cation exchange resin. This suggests that the capacity to retain NO3 - is more dependent on the porosity of the material rather than its charge properties. Biochar had an ability to sorb and subsequently release a significant amount of NH4 + over the experimental period. The results indicated that adsorption through ion exchange plays the major role in this process. There were only small differences in sorption behavior between the three kinds of biochar from different feedstock materials.