Nitrogen Dynamics Affected By Biochar and Irrigation Level in an Onion Field.

Biochar as a soil amendment has the potential to improve nutrient availability, increase plant uptake, and reduce environmental loss. The objective of this research was to investigate N dynamics affected by biochar and irrigation level for onion production. A field experiment was conducted with biochar amendment and irrigation water amount treatments. Surface drip irrigation and fertigation in raised beds were used. Monitored treatments included amendments of softwood feedstock biochar and biochar plus manure at two irrigation levels (100% and 75% of water supply to maintain a reference soil water content). Ammonia (NH₃) and nitrous oxide (N₂O) emissions, N₂O production in soil, and soil pore water N concentration below the rooting zone were determined during the growing season. Fertilizer application event and irrigation level impacted NH₃ and N₂O emissions more than biochar amendments. Nitrogen leaching risk was high based on increased or much higher soil pore water N (>95% as nitrate, NO₃^-) concentrations at 50 cm depth compared to those at the 25 cm that continuously decreased with time at both irrigation levels. The field data did not show that biochar amendments reduced N volatilization and leaching losses. Yield and N use efficiency (NUE) will be determined upon harvest.  This research has illustrated the challenges in N management in irrigated vegetable crop production and multiple factors must be considered in the effort to use biochar amendment to increase NUE and reduce environmental loss.