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 (NO3−) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO3− loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct (P = 0.021), with greater soil-NO3− and biochar-NO3− 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 NO3− within the rhizosphere of biochar-amended soils which has implications for NO3− loss and improved nitrogen use efficiency.