Biochar Effects On Ryegrass Growth, Nutrient Leaching and Greenhouse Gas Emission in Norwegian Soils.

In Norway, Biochar appears as the technology with the largest potential to store C in agricultural soils, as underlined by a recent report of the Norwegian Climate and Pollution Agency. Future implementation of biochar technology requires a thorough investigation of its agronomic benefits and environmental effects. Here we report on a first set of two greenhouse experiments, where we tested biochar effects on ryegrass yield and nutrient content, soil nutrients and water content, and nutrient leaching and greenhouse gas emissions. We tested different proportions of wheat-straw biochar added to a 2-mm-sieved silty sand from the Ap horizon of a Fluvic Cambisol. Overall, biomass yields were not significantly modified by biochar treatment of up to 50 Mg DM ha^-1. However, a slight decrease in yield with biochar addition was observed when N-fertilization was 40% lower than recommended rates. At standard N application rates, biochar application consistently decreased Ca and Mg concentrations of ryegrass plants. Reduced plant N concentrations were also observed at the first two harvests, while no consistent effect was observed on plant P concentrations. In both greenhouse experiments, biochar addition significantly increased the soil water content. Preliminary results indicate that CO₂-flux rates from soil columns were not affected by biochar addition. This suggests that biochar structures remained stable in soil. Preliminary results also suggest that biochar addition at 50 Mg DM ha^-1 substantially decreased both nitrate leaching and N₂O emissions in the first month of the soil column experiment. In conclusion, the untreated wheat-straw biochar slightly immobilized major cations and N, which suggests that biochar should be pre-treated (e.g.  with manure). Reductions in both nitrate leaching and N₂O emissions by biochar appear as an important additional environmental benefit of the technology, which should be further investigated in field experiments.