Localisation of nitrate in the rhizosphere of biochar-amended soils

A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha −1 vs. control). Nitrate (NO 3 −) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO 3 − loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct ( P = 0.021), with greater soil-NO 3 − and biochar-NO 3 − contents in the high biochar treatment. Biochar addition increased wheat root length ratio ( P = 0.053) and lowered root N uptake ( P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO 3 − within the rhizosphere of biochar-amended soils which has implications for NO 3 − loss and improved nitrogen use efficiency. ► Biochar localises nitrate within the rhizosphere of wheat. ► N concentrations differed in rhizosphere, bulk and biochar environments. ► Biochar increased root length ratio, but decreased root N uptake. ► Results indicate a biochar and nutrient use efficiency synergy.