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 (N 2 O) fluxes in a tropical Arenosol planted to maize. Methods: A ten-day in situ 15 N pool dilution and N cycling experiment, using tracer amounts (0.1 g m -2 ) of 15 N labeled ammonium ( 15 NH 4 + ), nitrate ( 15 NO 3 - ) or 15 N-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 NO 3 - 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.