Pigeon pea biochar addition in tropical Arenosol under maize increases gross nitrification rate without an effect on nitrous oxide emission

Aims: To assess how biochar addition in rainfed conservation agriculture affects short-term transformation, plant uptake, retention of nitrogen (N) in soil, and nitrous oxide (N2O) fluxes in a tropical Arenosol planted to maize. Methods: A ten-day in situ 15N pool dilution and N cycling experiment, using tracer amounts (0.1 g m-2) of 15N labeled ammonium (15NH4+), nitrate (15NO3-) or 15N-urea, was carried out seven weeks after planting of maize (Zea mays L.) under conservation agriculture in Zambia, using planting basins without (CA) and with pigeon-pea biochar (BC) addition (4 t ha-1). Results: Pigeon-pea biochar increased soil NO3- concentration, gross nitrification rate, 15N recovery in extractable soil NO3-, and soil moisture. However, effects of biochar on soil N retention and plant N uptake were not significant. Likewise, biochar did not affect N2O fluxes. Conclusions: At low dosage, pigeon pea biochar has a positive effect on gross nitrification rate but does not affect short-term N retention in soil, N2O fluxes, nor does it help increasing the uptake of N by maize.