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, 15 N recovery in extractable soil NO 3-, and soil moisture. However, effects of biochar on soil N retention and plant N uptake were not significant. Likewise, biochar did not affect N 2 O 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, N 2 O fluxes, nor does it help increasing the uptake of N by maize.