Nitrogen Cycling Dynamics and Gaseous Nitrogen Losses from Irrigated Maize in the Sudan Savanna of Kano State, North West Nigeria

This study quantifies nitrogen cycling dynamics and gaseous nitrogen losses from irrigated maize production in the Sudan savanna of Kano State, located in Nigeria's North West geopolitical zone. Nitrogen use efficiency in irrigated cereal systems is typically low due to multiple loss pathways, yet quantitative data on the relative magnitude of denitrification, volatilisation, and leaching losses from Nigerian irrigated systems are almost entirely absent from the published literature, representing a critical gap in understanding the nitrogen economy of the Kano irrigation belt. Using a field experiment with 15N-labelled urea applied at three rates (60, 120, and 180 kg N per hectare) under irrigated maize, nitrogen uptake by plants and recovery in soil were traced over one complete growing season using isotope dilution methodology. Gaseous nitrogen losses were measured by the closed chamber technique for ammonia volatilisation and nitrous oxide emission simultaneously. Soil mineral nitrogen dynamics were monitored by in situ resin core method. Findings revealed that 15N recovery in plant biomass ranged from 32 to 41 percent across rates, with the remainder partitioned between soil residual (21 to 26%) and unaccounted losses (33 to 47%). Ammonia volatilisation accounted for 18 to 24 percent of applied N, peaking in the first seven days after surface urea application. Denitrification losses were small (3 to 6%) under aerobic conditions but increased significantly after heavy irrigation events. The study recommends urea deep placement and use of nitrification inhibitors as targeted loss-reduction strategies for Kano irrigated maize. Keywords: nitrogen cycling, gaseous nitrogen losses, 15N tracer, irrigated maize, Kano State.