Biochar from Various Sources at Different Application Rates Suppresses Nitrification Activity and N₂O Emissions in Soil

The nitrogen use efficiency (NUE) of maize is usually below 60%. Considering future food supply and climate change, selective breeding of maize with high nitrogen (N)-efficient varieties, covering genetic diversities, is an effective strategy for identifying specific elements for con trolling NUE and productivity per arable farming unit while reducing environmental damage. This study evaluated the yield and nitrous oxide (N2O) emission of 30 maize varieties under two different N doses of 57.5 kg N ha 1 (N1, N-sufficient) and 173 kg N ha 1 (N3, N-high) applied in two equal splits on 2 and 4 weeks after germination (WAG). Then, the tested maize varieties were categorized into four groups based on the grain yield and cumulative N2O, that is, efficient-efficient (EE) under both N1 and N3, high-N efficient (HNE) under N3 only, low-N efficient (LNE) under N1 only, and nonefficient-nonefficient (NN) under neither N1 nor N3. Maize yield was significantly positively correlated with shoot biomass, N-accumulation, and kernel-number under N1 and with N2O-flux at 5 WAG, NH4+, shoot biomass, and all of yield components under N3, whereas cumulative N2O showed a significant positive correlation with NO3under N3 only and with N2O flux at 3 WAG under both N levels. The EE generally showed higher grain yield, yield components, N-accumulation, dry matter accumulation, root volume, and NH4+ in soil and lower cumulative N2O and NO3 in soil relative to NN maize varieties. The EE variety groups of maize can be a feasible strategy for increasing N fertilizer efficiency without reducing maize production as well as decrease the negative impact of N lost in agricultural system.