Effects of biochar on volatilization of ammonia from tomato soil and its mechanism

We compared three commercially available types of biochar, originating from wheat straw, wood chips, and apricot shells, for their performance during tomato plant cultures on reducing soil ammonia volatilization. Pot experiments and field experiments were conducted, and the underlying mechanisms were characterized. Application of apricot shell biochar most strongly reduced soil ammonia volatilization, both in pot and field trials. In the pot experiments, this biochar decreased the ammonia volatilization rate by as much as 46.2% ( P < 0.05) and the cumulative volatilization by 21.0% ( P < 0.05) compared to a biochar-free control. Field tests demonstrated that during tomato cultivation, ammonia volatilization in the soil mainly occurred during the fruiting stage; here, the cumulative ammonia volatilization decreased by 37.5% following apricot shell biochar addition ( P < 0.05). Furthermore, apricot shell biochar decreased the ammonium concentration in the soil, by 46.5% and 40.4% in pot and field experiments, respectively ( P < 0.05). The treatment did not change the ratio of ammonia-oxidizing soil archaea and bacteria. The superior activity of apricot shell biochar was attributed to its large specific surface area, alkaline pH (9.63) and high content of lactone groups. The adsorption capacity of apricot shell biochar for ammonium in solution was 2.89 and 13.52 times higher than that of wood chip and wheat straw biochar, respectively, indicating that ammonium adsorption contributed to the beneficial effect of apricot shell biochar to reduce ammonia volatilization. This work demonstrate that biochar produced from apricot shells can strongly reduce ammonia volatilization and prevent nitrogen loss from the soil during tomato cultivation. ● Ammonia volatilization from the soil is highest at the fruiting stage of tomato. ● Biochar produced from apricot shell can effectively reduce ammonia volatilization. ● At tomato fruiting stage, ammonia volatilization is most effectively inhibited. ● The activity is due to lactone groups and high specific surface area of the biochar.