Maize biochars accelerate short-term soil nitrogen dynamics in a loamy sand soil

Biochar addition to soils has been proposed as a means to increase soil fertility and carbon sequestration. However, its effect on soil nitrogen (N) cycling and N availability is poorly understood. To gain better insight into the short-term effects of biochar on gross N transformation processes, a 15N tracing experiment
in combination with numerical data analysis was conducted. An arable loamy sand soil was used and mixed with two silage maize biochars, produced at 350 °C and 550 °C. The results showed accelerated soil N cycling following biochar addition, with increased gross N mineralization (185-221%), nitrification (10-69%) and ammonium (NH4+) consumption rates (333-508%). Moreover, transfer of N from a recalcitrant soil organic N (Nrec) pool to a more labile soil organic N (Nlab) pool was observed. In the control treatment, 8% of the NH4+ mineralized from Nlab was immobilized to the Nrec pool. In contrast, 79% and 55% of the NH4+ mineralized from Nrec were immobilized to the Nlab pool in the treatment with biochar-350 °C and biochar-550 °C, respectively. NH4+-N was adsorbed quickly to biochar at the start of the experiment, thereby buffering plant-available N. In conclusion, these types of biochar accelerated soil N transformations in the short term, thereby increasing soil N bio-availability, through a combined effect of mineralization of the recalcitrant soil organic N pool and subsequent NH4+ immobilization in a labile soil organic N pool.