Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil–plant relations

The application of pyrogenic carbon, biochar, to agricultural soils is currently discussed as a win-win strategy to sequester carbon in soil, thus improving soil fertility and mitigate global warming. Our aim was to investigate if biochar may improve plant eco-physiological responses under sufficient water supply as well as moderate drought stress. A fully randomized greenhouse study was conducted with the pseudo-cereal Chenopodium quinoa Willd, using three levels of biochar addition (0, 100 and 200 t ha-1) to a sandy soil and two water treatments (60% and 20% of the water holding capacity of the control), investigating growth, water use efficiency, eco-physiological parameters and greenhouse gas (GHG) fluxes. Biochar application increased growth, drought tolerance and leaf-N- and water-use efficiency of quinoa despite larger plant–leaf areas. The plants growing in biocharamended soil accumulated exactly the same amount of nitrogen in their larger leaf biomass than the control plants, causing significantly decreased leaf N-, prolineand chlorophyll-concentrations. In this regard, plant responses to biochar closely resembled those to elevated CO2. However, neither soil- nor plant–soil-respiration was higher in the larger plants, indicating less respiratory C losses per unit of biomass produced. Soil-N2O emissions were significantly reduced with biochar. The large application rate of 200 t ha-1 biochar did not improve plant growth compared to 100 t ha-1; hence an upper beneficial level exists. For quinoa grown in a sandy soil, biochar application might hence provide a win-win strategy for increased crop production, GHG emission mitigation and soil C sequestration.